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WOOD VENEER: LOG SELECTION, CUTTING, AND DRYING

Forest Service U.S. Department of Agriculture Technical Bulletin No. 1577 Lutz, John F. 1977. Wood veneer : log selection, cutting, and drying. U.S. Dep. Agrie, Tech. Bull. No. 1577, p. 137 Summarizes current information on cutting and drying veneer from many species of wood. Particular emphasis is placed on wood and log characteristics that affect veneer production; tech- niques for peeling, slicing, and drying veneer; and species involved.

KEYWORDS: Peeling, slicing, lathe, slicer, veneer quality, wood species, plywood, decorative panels, containers, thickness, physical properties, mechanical properties, grades. Oxford No. 832.20

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Stock No. 001-O0O-03723-4. WOOD VENEER: LOG SELECTION, CUTTING, AND DRYING

by John F. Lutz, Technologist, Forest Products Laboratory, Forest Service, U.S. Department of Agriculture The Laboratory is maintained at Madison, Wis. in cooperation with the University of Wisconsin.

Forest Service Technical Bulletin No. 1577 U.S. Department of Agriculture January 1978 PREFACE

The broad spectrum of veneer cutting and Curtis Peters, Harry Panzer, Joe Clark, and handling for a multitude of uses obviously cov- John McMillen stand out. ers a wide range of operations by many special- Other members of the Forest Service have ists, and involves hard-learned secrets. No one been particularly helpful with information on individual can be an expert in all areas—yet wood species, especially John Putnam and those his efforts must be in line with those of others involved with surveys of the forest resources. in research and industry. In these days of From representatives of the wood industry material shortages and pressure on energy have come advice, assistance, and encourage- sources, it seems doubly important to summa- ment. The contributors are legion, with partic- rize some of the principles and coordinate the ular help from Tom Batey of the American terminology. Plywood Association and Bill Groah of Hard- This bulletin is a view of the art of veneer wood Plywood Manufacturing Association on manufacture as seen by a specialist who spent many phases. the last 25 years in research and industry con- In preparing this bulletin, the author relied tacts. It represents an attempt to tie together heavily on three research publications he had the experiences of many for the benefit of all. written earlier. These three were published as Contributions to this web of information U.S. Department of Agriculture Forest Service have come from literally hundreds of people Research Papers, by the Forest Products throughout the United States. The references Laboratory. These were: listed here represent noteworthy contributions, ''Wood and Log Characteristics Affecting but only a few of them. Harder to document Veneer Production,'' by John F. Lutz, USDA are the thoughts and philosophies that have Forest Service Research Paper FPL 150, 1971. been shared with the author over the last quar- "Veneer Species That Grow in the United ter century. States,'' by John F. Lutz, USDA Forest Service Outstanding among these have been the con- Research Paper FPL 167,1972. tributions of other members of the Forest "Techniques for Peeling, Slicing, and Dry- Products Laboratory staff. The research efforts ing Veneer," by John F. Lutz, USDA Forest and considered judgment of H. 0. Fleischer, Service Research Paper FPL 228, 1974.

Use of trade, firm, or corporation names in this publication is for the infor- mation and convenience of the reader. Such use does not constitute an official endorsement or approval of any product or service by the U.S. Department of Agriculture to the exclusion of others that may be suitable.

11 CONTENTS

Page

Introduction Wood and log characteristics affecting veneer production 1 Veneer quality as related to end uses ^ Hardwoods or softwoods for veneer 2 Physical properties of wood ^ Mechanical properties of wood -'■^ Properties of veneer logs ^^ Veneer from wood species that grow in the United States 21 Techniques for peeling, slicing, and drying veneer 29 Log storage ^^ Bark removal ^^ Sawing into bolts or flitches ^^ Conditioning wood prior to cutting veneer 34 Veneer cutting equipment 45 Knife and pressure bar on lathe and slicer ^^ Conveying and clipping veneer ^^ Veneer drying '^^ Quality control '^^ Veneer yields and volume needed for a plant 87 Veneer yields (rotary cutting) 87 Veneer yields (sliced) 87 Volume of timber needed to set up a veneer plant 88 Literature cited 89 Appendix I—Nomenclature of wood species and veneer 91 Appendix II—Physical properties of U.S. woods for veneer 95 Appendix III—Mechanical properties of U.S. woods for veneer Ill Appendix IV—Some processing variables of U.S. woods for veneer 116 Appendix V—Effects of log storage and processing on veneer characteristics 121 Appendix VI—Appearance and suitability of individual U.S. species for various uses of veneer 125 Glossary 133 Index 135

Requests for copies of illustrations contained in this publication should he directed to the Forest Products Laboratory y U.S. Department of Agriculture, Forest Service, P.O. Box 5130, Madison, Wis. 53705. iii

WOOD VENEER: LOG SELECTION, CUTTING, AND DRYING

INTRODUCTION

The wood veneer industry uses over a thou- for veneer. Other U.S. species received closer sand different wood species to make products looks for this product, and species from other as diversified as rotary-cut box shook VL inch countries are being imported into the country (6.35 mm) thick to sliced decorative face in an increasing swell of species, qualities, and veneer Vioo inch (0.25 mm) thick. In the United quantities. States, the major veneer uses are for structural All of this has required more information— and industrial plywood components % to 1 inch information that has been pieced together (9.25 to 25.40 mm) thick and decorative wall painstakingly. Material on individual species is panels and furniture parts ?l6 to 1 inch (4.76 compiled for the benefit of the reader in the to 25.40 mm) thick. tables of the Appendix. But, whenever possible, With such a wide array of raw materials and the text of this bulletin tries to present the final end uses, the field may at first seem overly generalized approach, and for native U.S. complex. In part, this may be due to the scar- species. city of written information summarizing the Common names of wood species are generally technical aspects of wood veneer manufacture. given in this publication. But experienced users This bulletin describes the basic information are well aware of the pitfalls of common names. known about the processes used in manufacture Therefore, the corresponding official name of of wood veneer. Wherever possible, the log the tree from which the wood comes is shown selection, log heating, veneer cutting, and dry- in Appendix I, along with the specific botanical ing processes are generalized and described as name. a continuum. To be sure, many individual proc- essing problems are related to specific wood The information contained herein comes species. However, whenever possible the under- from Forest Products Laboratory publications, lying cause is described and a generalized ap- from other research organizations, and from proach to the problem is suggested. contacts with the veneer and plywood industry. Still, it is impossible to avoid some effects of The bulletin is written primarily for people individual species. In the past, when only a responsible for some part of the veneer manu- comparatively few species were used for facturing process. It may also be of interest to veneer, this was not a great problem. It began others, including those growing trees for use to increase, however, as the favored species as veneer, for log buyers, users of veneer, and could not continue to meet increased demands wood technology students.

WOOD AND LOG CHARACTERISTICS AFFECTING VENEER PRODUCTION

A successful veneer operation depends on veneer, the logs must have the appropriate three items: A supply of suitable logs, good wood and log characteristics. The desired wood processing techniques, and a good sales organi- and log characteristics, in turn, depend on the zation. Most important is an adequate supply end uses of the veneer. of suitable logs. Then to produce suitable VENEER QUALITY AS RELATED TO END USES In this bulletin, veneer is defined as wood the stiffest and strongest and group 5 the least cut Vioo to % inch (0.26 to 6.35 mm) in thick- stiff and strong. Properties that are considered ness by a knife, whether by rotary or slicing include bending (modulus of elasticity and methods. Three characteristics of veneer that modulus of rupture), compression parallel and are desirable for all end uses are uniformity of perpendicular to the grain, and shear. thickness, minimum surface roughness, and Classification of species of veneer specified minimum buckle. For decorative face veneer, in Product Standard PS 51-71 for Hardwood control of figure, color, and depth of checks and Decorative Plywood is given in table 3. As into the veneer are important. Other veneer indicated in the table, the classification is based containing natural defects, such as knots, knot- on specific gravity. Face veneer for decorative holes, splits, and discoloration, can be used as plywood is graded primarily by appearance. inner plies in many products and as faces of Species for use in wirebound boxes as speci- some products like sheathing and container ply- fied in Federal Specification PPP-B-585b are wood. listed in table 4. The four groups are based on Four broad categories and typical end uses specific gravity and other properties of impor- of veneer are given in table 1, as well as some tance in containers such as strength as a beam, wood qualities as they relate to uses of veneer. resistance to nail withdrawal, shock resistance, The classification of species of veneer speci- and tendency to split when nailed or stapled. fied in Product Standard PS 1-74, Construction An indication of the importance, for specific and Industrial Plywood, is listed in table 2. The end uses, of all of the wood and log properties classification is based primarily on the stiffness that are discussed in this paper is shown in and strength of the species. Group 1 woods are table 5.

HARDWOODS OR SOFTWOODS FOR VENEER Most species can be successfully cut into The reasons for the better bending proper- veneer. However, some are much easier to ties of hardwoods are not definitely known. Two process than others. Hardwoods, as a class, are possible explanations are that the hardwoods easier to cut into veneer than softwoods. This have less lignin than the softwoods, and that probably is because hardwoods can be bent lignin in hardwoods is more thermoplastic than more readily than softwoods (65) ^ All veneer the lignin in softwoods. bends severely as it passes over the knife that While construction and industrial plywood is separates it from a bolt or flitch. Hardwoods, generally made from softwoods, hardwoods are having better bending properties, bend with preferred for most other uses listed in table 1. less damage as checks in the veneer than do Good bending properties are particularly useful softwoods. for some types of furniture.

1 Italicized numbers in parentheses refer to Litera- ture Cited. PHYSICAL PROPERTIES OF WOOD Generally, the first information about a spe- same category as West Coast Douglas-fir. The cies is obtained by a wood taxonomist or wood minor southern pines, which have lower specific anatomist. Working with herbarium material gravities, did not meet these requirements. and small wood samples, he classifies the spe- Thus, while not foolproof, specific gravity can cies and describes its structure. This informa- be used to quickly screen new species for ten- tion is valuable for screening species to be con- tative classification. sidered for use as veneer. Such information is While most species can be cut into veneer often available from libraries or by contacting by suitable manipulation of the cutting condi- Federal and State wood research laboratories tions, it is more difficult to cut wood at the two or wood technology departments of forestry extremes of the range of specific gravity. Very schools throughout the world. lightweight species tend to cut with a fuzzy Physical properties of wood of interest to surface. Dense species require more power to potential veneer producers include specific grav- cut and tend to develop deep cracks in the ity, moisture content, permeability, shrinkage, veneer as it passes over the knife. Basswood, extraneous cell contents, figure, odor, and cell with a specific gravity (based on green volume size, type, and distribution. (Values for individ- and ovendry weight) of about 0.32, is toward ual species are given in Appendix II, 'Thysi- the low end of the range for species that are cal Properties of U.S. Woods for Veneer.") successfully cut into veneer. Hickory, with about 0.65, is near the high end. Still, a valu- able species like rosewood, specific gravity of Specific Gravity 0.75, can be successfully sliced into face veneer, Specific gravity or density is easily obtained but this requires suitable heating and limiting and is often one of the first properties known the cutting to thin veneer. about a species. As indicated in table 1, it can In gluing, also, the denser the wood the more be used as a general guide in screening woods difficult it generally is to glue (62), for use as veneer. For example, a wood with Typical specific gravities of woods used for moderately low specific gravity is preferred construction plywood are 0.41 to 0.55 ; for hard- for use as core and crossbands of decorative wood face veneer 0.43 to 0.65; for core and plywood. crossband veneer of decorative panels from 0.32 to 0.45; and for container veneer from Detailed information is available about the 0.36 to 0.65 (table 1). Obviously, there are variation in specific gravity of many species, exceptions to these general guidelines. For ex- and additional data are being collected for other ample, butternut, with a specific gravity of species. Information on the specific gravity of 0.36, is a high-value face veneer. It is suitable wood species can prove commercially valuable. for wall paneling but less suitable where hard- For one example, knowledge of specific gravity ness is a factor, such as the top of a desk. for the various pines proved important in founding the southern pine plywood industry. When this industry started, the question was Green Moisture Content asked if all species of southern pine could be Veneer is often cut from logs soon after the used and still make a product that could be trees are felled. Such bolts or flitches have marketed in the same strength category as essentially the moisture content found in the Douglas-fir for structural softwood plywood. living tree. This moisture content in the wood (Species are placed in various groups for use has a distinct effect on cutting. In general, as structural plywood primarily on the basis of wood with a moisture content above fiber satu- stiffness and strength; in general, the strength ration but not excessively high is best suited of wood is related to specific gravity.) for cutting into veneer; this makes the wood Based on the recorded strength values and more pliable than drier wood. In a number of specific gravity records, the major southern studies we found that species with a natural pines—loblolly, longleaf, shortleaf, and slash uniform moisture content of about 50 to 60 pine—were permitted to be marketed in the percent cut well. *S O Ö Q) Ö C3 *S I J bû— ^ M TH ^ Q) tí O O P S bJO „

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O ftPL, > CÖ ^ pL, PH PH lO O §1 îs U Some of the free water is forced out during cutting. This water apparently acts as a lubri- cant between the wood and the knife and pres- sure bar and aids the cutting process. The driest wood that we have cut success- fully into veneer at the Forest Products Laboratory was a flitch of teak with a moisture content of 25 percent. Like all teak, this flitch had a waxy extractive that probably aided the cutting. We tried cutting even drier wood, but were not successful. This came about because a man- ufacturer wanted to slice air-dried planks of ponderosa pine into veneer VLG inch (1.50 mm) thick. The wood, which was at about 15 percent moisture content, was heated to about 200° F in water. Continuous sheets of veneer were pro- duced from the flitches but the veneer had pro- nounced checks on the side that was next to the knife during cutting. After cutting, the veneer sheets immediately curled into tight rolls like window shades, so they were unsatis- factory. M 88966 Because slicing of the wood at 15 percent Figure 1.—"Shelling" or shattering of redwood veneer that was rotary-cut from a "sinker" log. The wood moisture content was unsuccessful, we took shattered because water was forced out of the wood sapwood air-dried planks from the same ship- too fast during cutting. ment, and pressure-treated them with water to a moisture content of over 100 percent. Veneer that high moisture content in "sinker" logs of Vie inch (1.59 mm) thick was then successfully species like redwood makes them undesirable sliced from these planks. In other words, when for veneer because of cutting and drying prob- water is put back into relatively dry wood, the lems. Likewise, for a long time sapwood veneer wood can be cut into veneer. of Douglas-fir was not considered A-grade; Some species have a higher moisture content part of the difficulty was in cutting it into in one part of the tree than another. For smooth veneer as easily as the heartwood, example, the sapwood of Douglas-fir has ap- which has a lower moisture content. proximately three times as much water as the Wood may be damaged by freezing if it is heartwood. Butt logs of redwood often have stored in a cold climate. For instance, southern much higher moisture content than upper logs. pine sapwood was damaged when logs were In addition to requiring long drying times, stored outdoors during the winter in Madison, wood having a very high moisture content is Wis. Even worse damage was observed in a more difficult to cut into veneer than wood of sweetgum log stored through a winter at Madi- the same species but with a lower moisture son when the temperature went from above content. Examples are some western hemlock freezing to as low as -20° F. The end of a bolt (as high as 215 pet), redwood (as high as cut from this log is shown in figure 2. Ice was 245 pet), and Douglas-fir (as high as 130 pet). found in many of the cracks seen on this end In normal veneer cutting, the wood is com- section. Industry reports that walnut logs pressed just ahead of the knife. Wood with a grown in California and shipped by rail to the very high moisture content can not compress East froze when crossing the Rocky Mountains. until some water is forced out. As water is rela- Veneer cut from those logs was nearly useless tively noncompressible, it is forced from the due to splits caused by freezing. wood structure so fast that it ruptures the Moisture content in the tree, then, is gener- wood (fig. 1). Commercial experience indicates ally not a decisive factor in determining Shrinkage A small degree of shrinkage is desirable for all wood that is to be cut into veneer. In gen- eral, low shrinkage is related to low specific gravity. The low shrinkage of teak and mahog- any is one reason these are preferred woods for face veneer. However, even within species hav- ing the same specific gravity, a considerable range of shrinkage exists. High shrinkage is undesirable because it; Puts more stress on plywood gluelines with changes in moisture content; may cause cracks in face veneer of crossbanded panels during service; and causes warping unless the cross- banded panels are perfectly balanced. Radial shrinkage is generally less than tan- gential shrinkage. Consequently, quarter-sliced veneer will often perform better as face veneer or cross band veneer than flat-sliced or rotary- cut veneer of the same species. M 84166 F Longitudinal shrinkage may also be a factor Figure 2.—Splits and shake in this sweetgrum log were in use of veneer. On several occasions we have caused by alternate freezing and thawing. seen thin decorative plywood panels bow seri- whether wood is suitable for use as veneer. ously because of the different longitudinal Wood with a very high moisture content is shrinkage characteristics of face and back usually more difficult to process than wood veneer. Excessive longitudinal shrinkage may having a moderate moisture content such as 50 be due to short grain, to compression wood in to 60 percent. On the other hand, it is very softwoods, or tension wood in hardwoods. difficult or impossible to cut good veneer from Shrinkage is a factor in all veneer uses but wood below the fiber saturation point, approxi- perhaps is most important for crossband mately 30 percent for all species. veneer. Drying conditions may affect the total shrink- Permeability age of refractory species like some eucalypts. Permeability has a distinct effect on veneer cutting, drying, and gluing characteristics. Sap- Wood Structure and Growth Rate wood is often more permeable than heartwood In general, it is desirable to have uniform of the same species. Bacterial attack in log wood structure for ease of cutting, drying, and storage may increase the permeability of wood, processing of wood into veneer. The relatively thereby changing its cutting characteristics. uniform structure, regardless of growth rate, is Wood that is permeable is easier to cut because one reason why diffuse porous hardwoods like water is readily forced from the wood; forces yellow-poplar, sweetgum, and yellow birch are that could rupture the wood do not develop. such good veneer species. Similarly, softwoods Furthermore, plywood made from veneer that like white pine and Klinki pine are good veneer is naturally permeable, such as yellow-poplar, species. Uniform structure is particularly de- is less subject to "blowout" in the hot press sirable for crossbands of decorative panels to than plywood made from such relatively imper- minimize "telegraphing" of the grain to the vious veneer as spruce. Extremely permeable face. veneer, such as the sapwood of pine that has Such species as Douglas-fir, southern pine, been attacked by bacteria, may require a heavy and the oaks have a pronounced difference in glue spread or changes in gluing techniques to density between springwood and summerwood. obtain satisfactory bonds. Assuming other factors are equal, veneer pro- ducers generally prefer slow-grown wood of affect the appearance of the finished wood sur- such species. In practice this is not always pos- face. If desired, the filler can be used to accent sible; for example, most construction plywood the figure of the wood. is made from Douglas-fir and southern pine, much of it fast grown. However, veneer from Straight vs. Irregular Grain slow-grown logs of these species cuts better, For ease of veneer processing and for most dries with less buckle, and is generally pre- end uses, straight grain is desirable. ferred by production personnel. For ease in Straight-grained wood is easier to cut than cutting and drying, veneer logs of such species irregular grain and the veneer is more likely to should have a minimum of six rings per inch. remain flat. On the other hand, the market Ponderosa pine growing in the Southeastern value of certain finished items of irregular grain United States often has 30 rings or more per may be high enough to pay for the extra care radial inch of growth. In tests at the Labora- needed in handling it. Examples are the curly tory, we found this to be excellent wood for grain in species like walnut and maple and cutting into veneer. interlocked grain in mahogany. The curly One of the problems that sometimes occurs grain often shows on a flat-cut or tangential with fast-grown softwoods is '^shelling,'' a local surface. Interlocked grain shows as a stripe on separation of the annual rings at the spring- quarter-cut or radial surfaces. Identifying wood-summer wood boundary (fig. 1). The first irregular grain in logs is discussed further few layers of springwood cells are apparently under ''Log Properties." weaker in resistance to shear than cells formed Geneticists are studying the inheritance of later in the year. Shelling may also occur with interlocked grain in species like red gum. Such slow-grown wood that has soft, weak spring- information would help in selecting straight- wood and high moisture content. Examples are grained trees to breed for lumber and veneer western redcedar and redwood. Shelling is ag- production. gravated by use of high compression by the nosebar and by excessive heating of the wood prior to cutting. Parenchyma Fast-grown wood of species such as Douglas- Parenchyma cells occur most frequently in fir and southern pine may cause problems in wood rays and as concentric bands at the edge drying, gluing, and finishing {W). of growth rings. These cells are comparatively The same relationship holds for ring-porous thin-walled and function primarily for storage hardwoods like oak. In such woods, it is desir- of food. They are generally weaker than most able that the springwood portion of the annual other wood cells and so may form zones of ring be narrow and the summerwood be of weakness when they occur in large bands. moderate density. In other words, the desirable Terminal bands of parenchyma in angelique thing is to get as uniform wood structure as make it difficult to rotary-cut that species with- possible. Such oak wood cuts well, does not shell out getting a "shelling*' type of failure at the readily between rings, and performs well as bands of parenchyma. To a lesser extent this furniture, paneling, or flooring. same problem occurred when rotary-cutting veneer from Brazil nut (fig. 3). Parenchyma in wood rays may be trouble- Texture some when quarter-slicing veneer. The cut will Open-grained or coarse-textured woods such be smooth when the knife moves across the as oak and ash have large pores. This is rela- wood in the direction in which the rays run tively unimportant in veneer cutting and dry- out at the surface being cut. Conversely, when ing but may be important in finishing. A furni- the rays run out at the surface in the direction ture wood with pores larger than those in birch opposite to the movement of the knife, the cut must have the pores filled to get a continuous is rough. In the first instance, the rays are com- film of finish. Large pores also affect the ap- pressed by the cutting action and so cut pearance of the wood. The size of the pores smoothly. In the second case, the rays are and the color of the filler used to fill them will stressed in tension perpendicular to the grain solvents such as water, alcohol, acetone, ben- zene, and ether. The range and mixture of extraneous com- pounds found in wood is very large (28). Many of them have not been fully identified. Further, íí^^ilrj the amount of extractives varies widely from tree to tree and often within a tree. Therefore, only a few of the extraneous materials that may affect the use of wood as veneer will be discussed here. In general, the extractives constitute only a small percent of the dry weight of the wood. In exceptional cases, however, such as the resin in longleaf pine stumps, the total may be as high as 20 percent. Often the high concentra- tion of extraneous materials that cause diflS- culties in processing veneer results from a tree's response to injury. Heavy oleoresin con- centrations are often found in southern pine trees that have been tapped for resin. Pitch pockets and blisters are generally considered to be caused by injury to the cambium of trees that secrete oleoresin. The wood contains pock- al: ii.,;,iüi5 i^ ets of oleoresin, which flows readily when the defect is cut open. Fires are reported to stimu- 1 4 late gum production in several species. Insect M 136 460 attack is considered a principal cause of gum Figure 3.—Separation of a parenchyma band in rotary- spots in black cherry. Wounding of hickories or cut Brazil nut veneer. The scale is in inches. pecans by cambium-boring insects often results in deposits of calcium carbonate or magnesium by the cutting action. As they are weak in ten- carbonate that are hard and large enough to sion, they split ahead of the knife into the wood and cause a rough surface. This phenomenon of nick a sharp knife. differing roughness of the surface also applies These examples suggest that the percentage to the orientation of annual rings and fibers of veneer logs free of objectionable concentra- (39). tions of extraneous materials can be increased in two ways: By selection of tree breeding stock that is resistant to insect attack, and by Extraneous Cell Contents and Some Effects silvicultural practices that minimize injury to Cellulose, hemicellulose, and lignin are the the trees. primary structural elements of the cell wall. The terminology concerning extractives is Being polymeric in nature they are essentially sometimes confusing to nonspecialists in this insoluble in water and neutral organic solvents. field. This problem is complicated because most Many other materials may also be present extractives consist of more than one compound. in the wood. They are not part of the wood structure, but they contribute to the wood such properties as color, odor, and resistance to Giim decay. They are grouped under the general The word "gum" has been used in the past heading of extraneous resins, waxes, hard de- to describe any plant exúdate that feels gummy posits, and the like. Gluing problems have some- when fresh and that hardens on exposure to times been attributed to resinous and waxy air. In recent years chemists have used the deposits in the wood. Extraneous materials can word "gum" specifically for certain types of generally be removed from the wood by neutral polysaccarides. True gum is more or less sola- ble in water and insoluble in nonpolar organic solvents. Arabinogalactan, which may be pres- ent in amounts sufficient to interfere with the gluing of veneer cut from butt logs of western larch, is a true gum. Gum spots in black cherry probably consist of true gum and polyphenols, with the polyphenols causing their dark brown color. While a slight amount of gum is per- mitted in cherry face veneer (7), moderate or heavy concentrations of gum lower the grade. Figure 4 shows the gum that limits use of Brazil nut for veneer.

Resin and Oleoresin In contrast to gum, resin denotes materials that are insoluble in water but soluble in neu- tral organic solvents. Resins occur in ray parenchyma cells of both hardwoods and soft- woods. Oleoresin is a mixture of resin and essential oils; it is insoluble in water but solu- ble in alcohol, alkalies, and most organic sol- vents. Oleoresin is secreted by vertical and hor- izontal resin canals in such softwood groups as pine, spruce, Douglas-fir, and tamarack. In hemlock, fir, and redwood, resin canals are nor- mally absent but may be produced by injury to the tree. In veneer cutting, resin is a handicap. It may collect on the pressure bar and encourage chips M 136 441 to jam between the pressure bar and the wood Figure 4.—Gum in a sheet of rotary-cut Brazil nut bolt, causing depressions in the veneer. Frozen veneer. or solidified resin in knots is very hard and will quickly blunt a sharp knife. These extractives may be part of the problem Ether-soluble resin occurs in small amounts in gluing kapur and keruing. in many U.S. hardwoods, but generally has little effect on their use for veneer. The relatively Polyphenols large amounts of ether-soluble components found in basswood may explain why this species Polyphenols can be broadly grouped into tan- is more difficult to glue than would be expected nins and nontannins. Most tannins are of a from its specific gravity. Resin in core and molecular size generally soluble in water. Poly- crossply veneers, such as may occur in the phenols that are not soluble in water can be heartwood of cativo and southern pine, is ob- removed from wood with polar organic solvents jectionable because it may bleed through the like alcohol or alcohol-benzene. Polyphenols face veneer. Similarly resin in face veneer occur in most species and are generally more species like white pine can interfere with fur- common in the heartwood than in the sapwood. niture finishes. This is particularly true if the end pi'oduct is a TV cabinet, which becomes Color warm during use. One reason polyphenols are important is be- Among the imported hardwoods, vertical and cause they give wood its typical color. Colored horizontal resin canals are found only in cer- heartwood of decorative face veneer of species tain species of Dipterocarpaceae. The contents like rosewood is much more valuable than light- of these canals usually appear white or yellow. colored sapwood.

10 Almost all sapwood is white. This light color Hard Deposits is preferred for some face veneer of species The ash content of wood is usually less than like maple. Light-colored wood may also be pref- 1 percent but in small areas in the wood it can erable for containers as it makes a good back- be much greater. The principal inorganic de- ground for stenciling or other markings. Color posits contain calcium, magnesium, or silica. is of little importance for construction plywood Concentrated minerals have a distinct blunting or for core and crossband veneers. effect on sharp tools. However, scattered indi- vidual crystals of calcium oxalate, which are Metal Stain common in the longitudinal parenchyma and Many polyphenols react with iron and steel ray cells of many hardwoods, do not obviously in the presence of water to form a blue-black affect veneer cutting. stain. This becomes very obvious and objection- Hard deposits that do cause rapid dulling of able on face veneer of species like oak and red- knives are limited to a few native species such wood if the wet wood is in contact with iron or as maple, pecan, and hickory. The ash content steel for even a brief time. Hot wet wood will in mineral streaks of hard maple is reported stain more readily than cold wet wood. to average 5.2 percent and to be high in man- ganese. Calcium deposits, concentrated in hick- Dimensional Stability ory and pecan that is injured by cambium- mining insects, will nick a sharp knife. Nearn (49) showed that many heartwood extractives will partially stabilize the wood In contrast to continental U.S. species, many dimensionally. One result is that dry, rotary- tropical hardwoods contain silica. If the silica cut heartwood veneer of species like yellow- content exceeds 0.5 percent, it causes rapid poplar and Douglas-fir has less end wrinkling blunting of cutting tools. and buckle than sapwood veneer cut from the same logs. Flat veneer is easier to handle in Figure plant processing than buckled or wavy veneer. Figure is defined as the pattern produced in a wood surface by annual growth rings, rays, Checks in Veneer knots, deviations from regular grain such as Checks in the heartwood veneer of rotary- interlocked and wavy grain, and irregular cut types are measurably deeper than checks coloration. Figure is one of the most important in the sapwood veneer cut under the same con- characteristics of decorative face veneer. How- ditions. Similarly, high-speed photographs have ever, for uses of veneer other than decorative shown that breaks into the heartwood veneer face stock, highly figured wood is generally not of yellow birch were more conspicuous than desired. breaks into sapwood veneer cut in the same revolution of the bolt. One possible explanation of these phenomena is that the polyphenols in Odor the heartwood make it less plastic than the Most woods have little odor when dry. Some sapwood. species, such as cedars, have a pleasant odor that is used to promote the use of the wood. Wax Other woods have a sour or unpleasant odor, A few species of wood have waxy extractives particularly if they become damp. Logs stored that seem to be an advantage when cutting in a warm climate may develop objectionable veneer. Pencil manufacturers recognize this odors due to the action of bacteria. The prob- advantage and add wax to incense-cedar pencil lem is most likely to occur with species that blanks to improve the whittling properties of have wide bands of sapwood containing large the wood. Conversely, waxy extractives make deposits of starch. Such odors are particularly wood more difficult to glue and finish. Examples objectionable in veneer that is to be used for of wood that feel waxy to the touch include products like food containers or paneling for teak, determa, and cypress. walls of homes.

11 MECHANICAL PROPERTIES OF WOOD Besides physical properties, the information is generally the critical factor for such struc- most generally available about a species is its tural uses as subflooring and roofing. mechanical properties. The most likely sources Modulus of rupture is a measure of the ulti- of information on mechanical properties of mate bending strength of the wood. It is of wood are libraries, Federal and State wood interest for containers and for construction research laboratories, and wood technology de- plywood. partments of forestry schools. Shear is important in structural applications Mechanical properties of particular interest such as the use of plywood as the web in a box for veneer are strength in tension perpendicu- beam. lar to the grain, hardness, modulus of elastic- When plywood is used as a stressed skin, ity, modulus of rupture, shear, and compres- strength in compression parallel to the grain sion parallel and perpendicular to the grain. is important. (Values for individual woods are given in Compression perpendicular to the grain is an Appendix III, ''Mechanical Properties of U.S. important property when a bearing load is Woods for Veneer.'') involved, such as a refrigerator on a plywood subfloor. A wood strong in tension perpendicular to the grain is desirable for veneer because it is Referring to end uses listed in table 1, con- less likely to split in log form, when cutting struction plywood is generally made from soft- into veneer, or in subsequent handling of the woods. A major reason is that, for a given veneer. specific gravity, softwoods generally have a higher modulus of elasticity than hardwoods. Hardness is of interest in veneer used for The longer cells and higher lignin content of furniture and flooring, or other places where the softwoods may account for the higher stiff- it will receive abrasion and impacts during ness. service. Softwood logs are also more readily available Modulus of elasticity, or stiffness, is impor- in large quantity and are less expensive than tant to veneer because stiffness of the plywood veneer-grade hardwood logs.

PROPERTIES OF VENEER LOGS Selection of species for decorative face "Ideal" Veneer Log veneer is based primarily on the appearance An "ideaF' veneer log is cylindrical in form of the wood. Other physical and mechanical with the pith in the geometric center of the properties are important for construction ply- log end sections. The bark surface of the log wood, core and crossband veneer, and container and the end sections are entirely free from veneer. blemishes. The annual rings on the end sections In addition to the wood properties of various indicate uniform slow growth so the specific species, their tree and log properties must be gravity and texture of the wood varies a mini- taken into account. The average diameter and mum amount. The grain of the log is straight. form of the trees are of obvious interest to any The minimum diameter of this ideal log is 14 timber user. At one time it was thought that inches if it is to be rotary-cut, 18 inches if it only prime logs, large in diameter and clear of is to be flat-sliced, and 24 inches if it is to be defects, could be used for veneer. While only quarter-sliced. partially true, this popular concept of an Very few logs meet the criteria of an ideal ''ideaF' veneer log nicely introduces the subject veneer log. But logs having other characteris- of log grades. tics may still be eminently suited and valuable

12 for veneer. For example, the most obvious ex- The same sort of change has occurred in the ception to this concept is if fancy face veneer requirements for hardwood face veneer. At one is planned ; here irregular grain of a particular time such veneer had to be perfectly clear. In type is desired. recent years such characteristics as small pin knots, insect tracings, and slight stain have been well accepted by the public for prefinished wall Function of Log Grades paneling, the major use for hardwood plywood. As a result lower grade logs are suitable for Wood is a natural product and has many manufacture into hardwood face veneer. variable characteristics. Such characteristics as sweep, log end splits, and knots are among the many factors evaluated when grading a log. Veneer Log Grades Based on all these considerations, the log While there are some formal veneer log grader estimates the quality and quantity of grades, many mills have their own local rules veneer that can be produced from the logs. For for acceptable logs. In their simplest form they example, one criterion for a No. 1 Douglas-fir specify minimum diameter and length of logs, peeler, as given by the official Log Scaling and and the size and number of permissible surface Grading Rules for five western softwood grad- defects, like knots. ing bureaus (58), is that it be suitable for man- Harrar (27) has described the frequency and ufacture of clear uniform-colored veneer, to an importance of defects in southern hardwood amount not less than 50 percent of the net and veneer logs. Grading rules for northern scaled content. Log quality used in softwood hardwood and softwood veneer logs are pub- plants today go from No. 1 peelers to almost lished by the Northern Hardwood and Pine any log that can be held by the lathe chucks Manufacturers Association (52). A guide to and turned into veneer. Hardwood Log Grading (51) describes a veneer log class. Veneer log scaling and grading of western softwoods have also been consolidated Changing Requirements for Veneer Logs into one set of rules (58). While plant managers and production fore- men would rather work with high-grade peeler Specific Characteristics of Interest for logs, the availability of raw material and the Veneer Logs changing end uses of veneer and plywood have The relative importance of any one charac- forced the veneer industry to handle lower teristic in a veneer log depends on the end use grade logs. Improved methods for handling of the veneer. For example, figured wood may small logs have made it practicable to manu- be desirable for hardwood face veneer but un- facture veneer from species like aspen, birch, desirable for core and crossband veneer. A sum- and southern pine with log diameters of 12 mary of some log characteristics and their rela- inches or less. Equipment developments such as tive importance according to the end use is retractable chucks, backup rolls, driven roller given in table 5. bars, and lathe chargers have permitted eco- nomic handling of lower grade lots (2), Diameter and Length One reason for this switch has been the change in the end use of the veneer. At one While it is true that logs as small as 10 time the main end products of the softwood inches (25.4 cm) or less are rotary-cut into plywood industry were such items as wall veneer, this is not the preferred diameter. Other paneling and faces for doors. Now the major factors being equal, large-diameter logs are use is structural C-D grade plywood. Knots as preferred for all veneer cutting. Large-diameter large as 3 inches in diameter and splits as wide logs mean less handling for a given volume of as 1 inch can be tolerated in this end product. veneer. Furthermore, better quality veneer can As a result, the raw material requirements be rotary-cut from large-diameter logs than have shifted from peeler grade logs to No. 1 those of small diameter. This is particularly and No. 2 grade sawlogs. true for thick veneer such as % inch (4.23 mm). 13 Log diameter is even more important for or compression wood. Sweep limits the number sliced veneer where the width of the veneer is of full-length sheets that can be produced from limited to the width of the flitch. The minimum the log. Sometimes sweep can be minimized by diameter of logs that are used for flat-slicing judicious bucking of the logs into bolts for is about 15 inches (38.1 cm) and for quarter- rotary-cutting, but individual bolts must be slicing, 21 to 22 inches (53.3 to 55.9 cm). straight. Slight sweep can be tolerated in logs In terms of log length, a species that does that are to be sliced, but the flitches should be not have a bole 8 feet (2.44 m) or longer is of so sawn that the sweep in the log is perpen- limited value for veneer. Most bolts that are dicular to the plane of the knife used in slicing. rotary-cut are 8 feet (2.44 m) long, even This will permit production of full-length though shorter bolts are cut for core plies, for veneers from the start of slicing. furniture, and for containers. Most face veneer slicers are 12 to 16 feet (3.66 or 4.88 m) long. Abnormal Wood While much of the sliced veneer is used in Logs with the pith off center often have ten- 8-foot (2.44 m) and shorter lengths, a premium sion wood or compression wood. Both of these is paid for 12- and 16-foot (3.66 and 4.88 m) forms of abnormal wood shrink more in length lengths. than normal wood and so cause buckling of the veneer during drying. Log Form Tension Wood For rotary-cutting, it is important that veneer logs have a cylindrical form with the Tension wood (57) is often found in leaning pith in the geometrical center of the log ends. hardwood trees. It is most pronounced in low- Laboratory and industry tests show that 5 to 6 density species such as cottonwood and aspen. percent of a typical veneer bolt is lost in round- Identifying characteristics in log form include ing it to obtain usable widths of veneer. an eccentric pith and silvery, crescent-shaped bands on the log cross section. When tension wood is pronounced, the bands are fuzzy or Taper and Eccentricity stringy, because the saw did not cut them Taper is more of a problem than slight eccen- cleanly (fig. 5). Tension wood is characterized tricity. Narrow widths of veneer are usable, but short length or fishtails generally are not. Taper also causes short grain in rotary-cut veneer. Such short grain is weak in bending and shrinks excessively in length. It may also lead to bleed-through of the glue in thin face veneer. Logs with pronounced eccentricity result in many narrow pieces of rotary-cut veneer. This veneer tends to be rougher than veneer cut from cylindrical logs because a part of each revolution of veneer is cut against the grain of the annual rings. Eccentric logs are also unde- sirable because they frequently have abnormal wood (55,57)—tension wood in hardwoods or compression wood in softwoods. Taper and eccentricity may also increase the amount of thick and thin veneer produced.

Sweep Sweep or lengthwise curvature of a log is a defect for both rotary and sliced veneer. For M 7.-. 160 Figure 5.—Tension wood in a cottonwood log is indi- one thing such logs often have tension wood cated by the arrow.

14 widely. Kubier (36) and others have demon- strated that the wood near the surface of the log is in tension in the longitudinal direction, while the wood near the center of the log is in compression in the longitudinal direction. In the transverse plane or cross section of the log, the wood is in compression near the outside of the log and in tension near the center of the log. In some cases these stresses cause the log ends to split as soon as the log is cut to length. Such an observation should serve as a caution sign when considering a species for veneer.

Log End Splits Due to Growth Stresses Splits that are in the log typically radiate from the pith like spokes of a wheel. When green wood is heated, it expands tangentially and shrinks radially, enlarging these splits (fig. 7). Splits are particularly bad in logs that are M 28426 F to be rotary-cut, because either the bolt is lost Figure 6.—Compression wood in a southern pine log is indicated in the outlined area. completely from splitting during cutting or from the corresponding splits in the veneer. by having little of the lignin that stiffens nor- Veneer splits are limiting defects as defined by mal fibers. As a result, the wood tends to bend the product standards for plywood (table 1 and cling to the knife rather than sever cleanly and U.S. Department of Commerce {63,64)). in veneer cutting. The cutting of tension wood can be improved by using an extra hard knife (such as a 62 to 64 on the Rockwell C-scale) and by keeping the knife very sharp. The wood is sometimes cooled to about 40° F with low- density species like basswood to improve the cutting of the softer wood.

Compression Wood Compression wood is typically found in soft- wood logs that have a pronounced eccentric pith. The crescent-shaped bands are most often found on the wide radius (fig. 6). They are dull, hornlike in appearance, and sometimes have a reddish cast. Compression wood is dense and superficially appears like extra-wide bands of summerwood. Because it is lignified, com- pression wood cuts well to form a smooth wood surface. However, the stresses in severe com- pression wood will often cause the green veneer to buckle. The buckle becomes worse in drying and may cause warping in plywood. Pillow (55) gives further information.

Growth Stresses M 136 337-1 Figure 7.—Splits in the end of a Brazil nut bolt. The Most species of wood have growth stresses. splits came from growth stresses in the tree and were However, the severity of these stresses varies greatly enlarged by heating the bolt to 200° F.

15 Log end splits are not quite so serious when the wood is to be sliced. The log can often be sawed to eliminate the major split by making the first saw cut through the split. It is some- times possible to eliminate other splits if the log is to be quarter- or rift-sliced. Even with careful cutting, some of the stresses in the tree are retained in the flitches. Consequently the flitches tend to bow toward the bark side, particularly during heating. Sometimes flitches are strapped together dur- ing heating to reduce this bow. The bow in the flitch that is to be flat-sliced can often be forced out when the flitch is mounted on the flitch- table before slicing. On the other hand, the bow in a quartered flitch is not changed when the flitch is mounted and sliced. Bowed veneer re- sults in considerable loss when the edges of veneer are made parallel by clipping. All in all, a species known to have marked growth stresses will generally yield more veneer by flat-slicing than by quarter-slicing.

M 87667 F Ring Shake Figure 8.—Knot sequence from the indicator on the Ring shake is another undesirable character- bark of Douglas-fir (1) to bolt diameters of 38 inches (2) ; 35 inches (3) ; 30 inches (4) ; 21 inches (5) ; and istic in logs to be used for veneer. Shake is 17 inches (6). accentuated by heating in water or steam, and there is no way of eliminating it. To prevent quency of knots is also related to species. Logs additional damage, plastic clips are sometimes of white fir and eastern hemlock, for instance, driven across the ring shake to help hold the have many more knots than species like noble bolt together during rotary cutting. The plastic fir, longleaf pine, and yellow-poplar. can be cut without damaging the knife edge. Some species have many knots because the Use of a roller bar rather than a fixed nosebar limbs persist for many years. For example, is reported to permit an operator to come closer limbs persist on Douglas-fir logs for up to 150 to shake without having the bolt break out. The years. In contrast, the limbs of southern pine roller bar exerts less drag on the bolt, so there frequently fall off a few years after they die. is less shear force to cause the wood to break One implication is when all logs come from at the ring shake. Shake is much more com- second growth, 100 years or less in age, the mon in old growth than in young trees. southern pines will furnish more knot-free veneer than Douglas-fir. Knot indicators are retained in the bark Knots many years after the limbs have been over- Knots are one of the most common and im- grown. The ability to recognize these indicators portant imperfections in veneer logs. Knots is a key factor in accurate grading of logs (37). may be sound and intergrown, encased, or de- How an indicator on the surface of a Douglas- cayed. Most encased or decayed knots fall out fir log signaled a serious defect is illustrated during the drying of veneer. Knot holes are in figure 8. more limiting defects in standard veneer The one exception to the degrading effect of grades than intergrown knots of the same knots is decorative veneer of species like west- diameter. ern redcedar and white pine. These specialized In general, there are fewer knots on logs of products call for flitches having sound inter- large diameter, on logs from trees grown in grown knots 1 inch or smaller in diameter. A fully stocked stands, and on butt logs. Fre- limited number of knots are permitted and are

16 desirable in some but not all decorative veneers Straight and Irregular Grain used as faces of paneling. Straight grain is generally considered desir- Epicormic branches and adventitious buds able for veneer logs. A typical commercial are relatively minor defects that occur on most veneer log grade will state that deviation from hardwoods, particularly elm, oak, maple, and straight grain shall not exceed so many inches sweetgum (37). They are not permitted in per foot of length of log. Spiral grain in the clear veneer for some furniture grades but are wood is often indicated by spiral grain in the accepted in many grades of wall paneling. bark. As described under physical properties of wood, straight-grained wood is easier to cut and dry and generally performs better in ply- wood panels than veneer having irregular grain. The one exception to this rule is for logs suit- able for decorative face veneer. In some cases irregular grain is desired because it enhances figure in the veneer cut from the log. The detection of figured wood in standing trees and logs is described in Pillow (56). Essentially the method is based on examining the bark and log end sections for inclination and waviness of the cellular structure of the wood. In some instances this can be detected from the rough outer bark. For example, yellow birch with a smooth bark is generally straight- grained, while that with rough irregular bark often contains curly grain or other grain irregu- * • 'M larities. Curly grain may not be apparent in the outer bark but if the outer bark is removed with a draw shave to reveal the soft layers of the inner bark, then the grain pattern can be seen. Figured wood may also be indicated by the shape of splits in the log end surface. If the splits have alternate zig-zag patterns, the wood will almost certainly have a pronounced figure. Another technique is to cut a small section from the log end in a radial direction and then if**r split this piece. The split will follow the grain direction and indicate if it is wavy or curly. Burls on the surface of the log may indicate that the entire log has irregular grain (figs. 9 and 10). Veneer that is figured throughout from small or large burls is often valued for its decorative effects. Other face veneers (table 1) are limited in the size and number of burls .^i^. that are permitted. Color In general a uniform color is desirable in veneer logs, but the color desired varies with M 91476 F the end use. Light-colored wood is appropriate Figure 9.—A bolt of black gum with many burls on for containers as it makes a good background the surface. Veneer cut from this bolt is shown in figure 10. for marking and is psychologically pleasing to

17 Gum Streaks and Pockets Gum streaks and pockets in hardwood logs can sometimes be seen on log ends. Large gum pockets may be detected as bulges on the log. While a small amount of gum can be permitted in some products, gum is generally regarded as undesirable.

Pitch and Pitch Pockets Pitch is found in one hardwood genus and in many softwoods like Douglas-fir, ponderosa pine, and southern pine. Massed pitch and pitch pockets are limiting defects in veneer (table 1).

Bark Pockets Bark pockets occur in some softwoods and in hardwoods like the oaks and hickories. They may show on the log ends or as overgrowths on the bark (37). Bark pockets are limiting defects for most veneer uses. M 92128 F Figure 10.—Burls in the sapwood (1) and heartwood Holes (2) of rotary veneer cut from the bolt shown in figure 9. The burls persisted to the 8-inch core of the bolt. Large holes such as those resulting from a the consumer. Maple logs with wide sapwood rotted branch stub or a woodpecker nest are zones are currently in demand because of the major defects in veneer logs. popularity of white face stock. In contrast, the Medium holes up to V2 inch (12.7 mm) in heartwood color is in demand for species like diameter—if extensive—may seriously degrade cherry and walnut. the log for use as veneer. Such holes may have Nonuniformity in color between logs can been made by grubs that tunnel in living trees cause problems. For example, the preferred like oak, or result from tapping sugar maple color of walnut is a light gray-brown. Green trees, from bullets, or from an increment borer. and purple tinges that sometimes occur in wal- Medium-size holes are generally accompanied nut are not wanted because they cause special by severe stain. problems in finishing. Pin worm holes made by ambrosia beetles Studies at the Forest Products Laboratory occur in hardwoods like oak and ash and also have shown that the color of walnut varies with in various softwoods. This defect can be par- the geographic area in which the trees grow. ticularly serious with tropical hardwoods. A There is some evidence that the color of walnut few scattered pin worm holes can be tolerated heartwood is related to the type of soil in in most veneer uses, but heavy attack seriously which the tree has grown. In addition, color in degrades the veneer. veneer can be regulated to some extent by the heating and drying process. Decay When a mixture of species, such as the Decay is a severe defect in veneer logs, lauans, is used, the material typically available especially for rotary cutting. If the log center for faces will display a variety of heartwood is decayed and soft, the chucks may not be colors. Recently some veneer and plywood man- able to hold the veneer bolts securely enough ufacturers have been using electronic devices to permit rotary cutting. Slightly or moder- to separate such veneer into several groups ately decayed logs can sometimes be cut into according to color. This simplifies the finishing veneer, providing the wood is still reasonably process, and aids in marketing the products. firm. The best example of this is Douglas-fir

18 that has been attacked by F ornes pini (white- of separating stains for practical purposes is pocket). Millions of square feet of softwood to consider those in the standing tree as op- plywood have been made from rotary-cut posed to those that may develop after the tree Douglas-fir veneer containing white-pocket. is felled. Sound ñitches for slicing can sometimes be sawn from logs with considerable decay. Stain in Standing Trees The terminology concerning stain in stand- Fire Scars ing trees is not well accepted. For example, some authors limit the term mineral stain to Fire scars are generally obvious on the cross small olive or greenish-black discolorations in section of a log, and often indicate associated the heartwood and sapwood of the maples and decay. Extensive fire scars make logs of doubt- the gums. Others use the same term to describe ful value for use in veneer. brown stains in species like aspen and oak. Still other authors attribute these and other Seams stains in oak and aspen and other hardwoods Seams are radial cracks that may or may not to oxidation of cell materials and call them oxi- be overgrown. They may be caused by wind, dation stains. Bacteria have also been reported lightning, or frost. Seams generally originate as associated with various stains in living trees. at the surface of the log and occur in the For purposes of this publication, stains in standing tree. In contrast, splits due to growth standing trees will not be separated. Stains stresses start at the pith and generally do not are found in both heartwood and sapwood of extend to the surface of the log. As a result, the living tree and are often associated with seams are visible on the standing tree but splits injury to the tree such as insect attack or are not. As seams occur through the cambium broken branches. layer they may be overgrown by callus tissue. In addition to the discoloration, intense areas Splits never have such overgrown tissue. Spe- of stain are more likely to collapse and check cies that may have seams include oak, ash, during drying. Higher ash content has been maple, beech, and birch. The seriousness of this found in dark green or black stained maple defect depends on how deeply it penetrates the than in normal bright wood. Some plant per- log and whether it is parallel to the log length sonnel report more rapid dulling of tools when or spiralled. A straight seam can be clipped cutting such stained wood. from the veneer with less waste than that Brown stain is common in oak trees growing caused by a spiralled seam. on upper slopes or ridge tops. Because of the poor growth site, these trees are generally also Bird Peck of poor form and do not supply many potential veneer logs. Oak trees growing on moist soils Bird peck and associated stain is a common that may be water-saturated for extended characteristic on such species as yellow-poplar periods are also subject to stain. Logs from and hickory. Bird peck can be detected by such trees may in other respects appear to be characteristic holes in the bark and by strain of quality suitable for veneer. on the log ends. Logs with this characteristic Stain in standing trees may be sporadic and are generally suitable for core and crossband localized to small streaks or it may occur over veneer but may be limited for use as face broad areas. Consequently, the stain may or veneer. may not be visible on freshly cut log ends.

Stain Stain that May Develap in Stored Logs or The term "stain'' has been used to describe Green Veneer several different phenomena. Causes of some Four types of stains that may develop in stains are known, such as fungal or contact stored logs or during veneer processing are sap with iron, while others are still being studied. stain, mold, oxidative stain, and iron stain. Further, the severity of some stains is directly Sap stain is fungal in origin and is most com- related to the amount of sapwood and the monly blue in color. It is particularly trouble- environment in which the log is held. One way some in the sapwood of species like sweetgum

19 and southern pine if the logs are stored during oxalic acid or hydrofluoric acid will bleach out periods of warm, humid weather. The color is iron stain. These acids must then be flushed caused by a concentration of hyphae. For many from the wood or the stain may reappear. veneer uses, blue stain is objectionable. It should Some references on stains originating during be controlled by keeping log storage to a mini- processing logs into veneer include Scheffer mum and, if necessary, by use of chemical (60) and Scheffer and Lindgren (61). sprays or water sprays. Veneer can be protected by drying the stock as rapidly as possible or by Man-Made Defects Other than Holes dipping or spraying with an antistain solution Man-made defects include stump pull, felling if drying is to be delayed. splits, log handling damage, and embedded Molds are also fungal in origin, but the color metal. (yellow, brown, red, purple, green, blue, or Stump Pull and Felling Splits black) comes mainly from spores of the fungi. Mold is characterized by a downy growth on Both these defects cause splits in the veneer the surface of the wood. Mild temperature, still cut from the logs. Stump pull is generally obvi- air, and abundant moisture promote growth of ous as a jagged hole on the long end. Butt logs mold. Under these conditions mold may be a should be carefully examined as felling splits problem in green sapwood veneer that is stored may close and be difficult to detect. 3 or more days before drying. Control methods Log Handling Damage are similar to those suggested for blue stain. Handling logs with tongs is a needless source Oxidative stain is a chemical stain that is of defect. Not only may the tongs put holes in thought to be the result of oxidation, sometimes otherwise clear veneer, but they also frequently promoted by enzymatic action on certain ma- embed sand or grit that damages the knife used terials stored in the wood cells. Like blue stain to cut the veneer. Similar problems occur with and mold, it develops in the sapwood of logs and logs that have dirt or gravel embedded in the green veneer when favorable moisture and tem- outer sapwood when the logs were dropped or perature exist. It has caused objectionable dis- damaged on a gravel or cinder surface. coloration of light-colored face veneers of species like birch and maple. In logs, the stain Embedded Metal progresses gradually in from the ends during Buried metal is a serious problem in logs cut warm-weather storage, so cold-weather storage from street trees and fence rows. Because or reducing storage time is the best method for barbed wire and nails will generally damage a preventing this stain. Use of a white lead paste veneer lathe or slicer knife, many veneer log end coating, or especially of a waterspray, dur- buyers will not purchase logs that come from ing storage may materially reduce this stain but along fences or streets. Buried metal may be will not stop it. Drying the veneer as soon as detected because it has formed a bump on the possible after cutting also reduces the chance of log. Many veneer mills have magnetic metal oxidation stain. Concentrated oxalic acid will detectors for screening all logs and flitches. generally bleach oxidation stain but not fungal- Soft lead from buck-shot and small arms can caused blue stain. be cut without damaging the lathe or slicer Tannin and other polyphenols react with iron knife. However, steel-jacketed bullets or shrap- and steel in the presence of water to form a nel such as may be found in timber from a blue-black stain. This becomes very obvious and battle zone are very serious defects. Aside from objectionable on face veneer of species like oak the damage to the knives used to cut the veneer, and redwood if the wet wood is in contact with buried metal often causes extensive stain in the iron or steel for even a brief time. Concentrated wood.

20 VENEER FROM WOOD SPECIES THAT GROW IN THE UNITED STATES

This chapter covers tree species that grow Information about the use of veneer from large enough and in sufficient volume in the various species is given in tables 6 and 7. The United States so that they can be considered for specific gravity figures given there help classify veneer. the species as in tables 2 to 4. While the use of veneer and plywood is in- The specific gravity figures for hardwoods creasing, the timber available in such well- can be used with the information in the next known veneer species as yellow birch and section to select a favorable range for heating Douglas-fir has declined. As a result, it is be- bolts or flitches prior to cutting veneer. coming more important to know the potential for making useful veneer from all species that The last four columns of table 6 and 7 rate the species for use in various products. Detailed grow in the United States. A number of species have been studied for information on log characteristics, wood char- use as veneer at the U.S. Forest Products Lab- acteristics, processing into veneer, and use of oratory. In addition, other Government labora- the veneer as related to wood species that grow tories and universities have published informa- in the United States is given in Appendixes II tion on veneer species. Still further information to VI. is available from the veneer industry. From Similar but abbreviated information on wood such sources scattered information has been species from around the world is given in the collected and condensed for this publication. If report, "Veneer Species of the World," pub- no published information was available on a lished in 1976 for the International Union of species for veneer, the species has been evalu- Forestry Research Organizations. Copies can be ated on the basis of the known physical and purchased from the National Technical Infor- mechanical properties of the wood. mation Service.^

2 The National Technical Information Service of the U.S. Department of Commerce is located at 5285 Port Royal Road, Springfield, Va. 22161. 21 Table 2.—Classification of species for construction and industrial plywood, PS 1-714.

Group 1 Group 2 Group 3 Group 4 Group 5 Apitong !• 2 Cedar, Port Orford Maple, black Alder, red Aspen Basswood Beech, American Cypress Mengkulang 1 Birch, paper Bigtooth Fir, balsam Birch Douglas-fir ^ Meranti, red ^' * Cedar, Alaska Quaking Poplar, balsam Sweet Fir Mersawa ^ Fir, subalpine Cativo Yellow California red Pine Hemlock, eastern Cedar Douglas-fir ^ Grand Pond Maple, bigleaf Incense Kapur 1 Noble Red Pine Western red Keruing i« 2 Pacific silver Virginia Jack Cottonwood Larch, western White Western white Lodgepole Eastern Maple, sugar Hemlock, western Spruce Ponderosa Black (western poplar) Pine Lauan Red Spruce Pine Caribbean Almon Sitka Redwood Eastern white Ocote Bagtikan Sweetgum Spruce Sugar Pine, southern Mayapis Tamarack Black Loblolly Red lauan Yellow poplar Engelmann Longleaf Tangile White Shortleaf White lauan Slash Tanoak

^ Each of these names represents a trade group of woods consisting of a number of closely related species. 2 Species from the genus Dipterocarpus are marketed collectively: Apitong if originating in the Philippines; Keruing if originating in Malaysia or Indonesia. ' Douglas-fir from trees grown in the states of Washington, Oregon, California, Idaho, Montana, Wyoming, and the Canadian Provinces of Alberta and British Columbia is classed as Douglas-fir No. 1. Douglas-fir from trees grown in the states of Nevada, Utah, Colorado, Arizona and New Mexico is Douglas- fir No. 2. * Red meranti is limited to species having a specific gravity of 0.41 or more based on green volume and ovendry weight.

Table 3.—Density categories of the most commonly used species based on specific gravity ranges for hardwood and decorative plywood, PS 51-71

Category A Category B Category C High-density species Medium-density species Low-density species (0.56 or more specific (0.43 through 0.55 (0.42 or less gravity) specific gravity) specific gravity) Ash, commercial white Ash, black Alder, red Beech, American Avodire Aspen Birch, yellow, sweet Bay Basswood, American Bubinga Cedar, Eastern red ^ Box elder Elm, rock Cherry, black Cativo Madrone, Pacific Chestnut, American Cedar, Western red ^ Maple, black (hard) Cypress ^ Ceiba Maple, sugar (hard) Elm, American (white, red, or gray) Cottonwood, black Oak, commercial red Fir, Douglas ^ Cottonwood, Eastern Oak, commercial white Oak, Oregon Gum, black Pine, white and ponderosa ^ Gum sweet Paldao Hackberry Poplar, yellow Pecan, commercial Lauan (Philippine mahogany) Redwood ^ Rosewood Limba Willow, black Sapele Teak Magnolia Mahogany, African Mahogany, Honduras Maple, red (soft) Maple, silver (soft) Primavera Sycamore Tupelo, water Walnut, American

1 Softwood.

22 Table 4.—Species^ for wirebound boxes as listed in Federal Specification PPP-B-585b

Group I Group II Group III Group IV Aspen (popple) Douglas-ñr Ash (except white ash) Ash, white Basswood Hemlock Elm, soft Beech Buckeye Larch, western Maple, soft Birch Cedar Pine, southern yellow Sweetgum Elm, rock Chestnut Tamarack Sycamore Hackberry Cottonwood Tupelo Hickory Cypress Maple, hard Fir (true firs) Oak Magnolia Pecan Pine (except southern yellow) Redwood Spruce Yellow-poplar Willow 1 Groupings are based on specific gravity and other properties of importance in container construction. When a group is specified, any species in the group can be used.

Table 5.—Importance of physical and mechanical wood properties and log characteristics as related to manufacture and use of the veneer

Construction Decorative Core and Container Property and indus- face crossband veneer Comments trial veneer veneer for and plywood decorative plywood panels Physical property Specific gravity A B A B Green moisture content B B B B-C Permeability B C B B-C Shrinkage B B A B Close grain B A-B A B-C Fine texture C B B C Straight grain A A-B A B Parenchyma B B B B-C Wax B B B B Polyphenols B B B B Color of heartwood C A C A-B Dimensional stability B B A B Resin B A A B Gum B A A B Hard deposits B A-B B B Figure C A C C Figure is desirable for face veneer and„j 1 ; _l-i_ f^- other uses Odor A Odor is important for con- tainers used with food. Mechanical property Strength in tension perpendicular to grain B B B B Hardness B B C B Modulus of elasticity A C C B Modulus of rupture A C C A Shear A C C C Compression perpendicular to grain A B C B Compression parallel to grain A C C B

23 Table 5.—Importance of physical and mechanical wood properties and log characteristics as related to manufacture and use of the veneer—continued

Construction Decorative Core and Container Property and indus- face crossband veneer Comments trial veneer veneer for and plywood decorative plywood panels Log characteristic Cylindrical form A B A B Taper A B A B Eccentricity B B B B Tension wood B A A B Compassion wood A B A B Sweep A B A B Growth stress B B B B Log end splits A B B B Ring shake A A A A Knots B A A B Epicormic branches and adventitious buds C B B C Burls B B B B Color C A C B Pitch pockets B A A B Pitch in crossbands may bleed through face veneer Bark pockets B A A B Grub holes B A A B Pinworm holes B B C B Heavy pinhole damage will degrade all veneer Decay A A A A Some types of decay are per- mitted in Construction grade plywood Fire scars B A A B Frost cracks B A A B Veneer from other parts of the log may be top grade Mineral streak C A C C Other stains C A C B Bird peck C A B B Stump pull A A A A Felling splits A A A A Handling damage A A A A Embedded metal A A A A Growth rate B A B B A—Of major importance Í B—Of moderate importance < These ratings are not hard and fast but are indicative of relative importance of various characteristics. C—Of little importance (

24 Table 6.—Specific gravity and suitability of some U.S. species for various veneer uses ^ Relative suitability Common Specific name gravity 2 Construction Decorative Inner plies of Container plywood face decorative veneer and veneer panels plywood

HARDWOODS Alder Nepal 0.34 C B A-B A Red .37 C B B B Ash Black .45 B A B A Blue .53 B A B A Green .53 B A B A Oregon .50 C A B A Pumpkin .48 C B C B Shamel .47 B A B A White .55 B A B A Aspen Bigtooth .35 C B A A Quaking .35 C B A A Basswood American .32 C C A A White — C C A A Beech, American .56 B B C A Birch Alaskan paper .49 B A-B B B Gray .45 C B B B Paper .48 B A-B B B River .49 B B B B Sweet .60 B A B B Yellow .55 B A B B Buckeye Ohio _ C C A B Yellow .33 C C A B Butternut .36 C A C C Cherry, Black .47 B A B A Cottonwood Balsam poplar 0.30 C B B A Black .31 C C B A Eastern .37 C C B A Swamp — C B B A Elm American .46 B A B A Cedar .59 B A C A Rock .57 B A C A Slippery .48 B A B A Winged .60 B A C A Eucalyptus .60 B A-B C B Hackberry .49 B A-B C A Hickory, pecan Bitternut .60 B A C B Nutmeg .56 B A C B Pecan .60 B A C B Water .61 B A C B Hickory, true Mockernut .64 B A C B Pignut .66 B A C B Shagbark .64 B A C B Shellbark .62 B A C B Holly, American .50 C A C C Honeylocust .60 C A C B Koa .53 B-C A B B-C Laurel, California .51 C A C C Locust, Black .66 C B C B Madrone, Pacific .58 C A C B

25 Table 6.—Specific gravity and suitability of some U,S, species for various veneer uses ^—continued

Relative suitability Common Specific name gravity 2 Construction Decorative Inner plies of Container plywood face decorative veneer and veneer panels plywood

HARDWOODS—continued Magnolia Cucumbertree 0.44 B C A A Southern .46 B C A A Maple Bigleaf .44 C A B A Black .52 B A B A Boxelder .41 C B C B Red .49 B B A A Silver .44 C B A A Sugar .56 B A B A Oak, red Black .56 B A B B California black .51 B A B B Cherrybark .61 B A B B Chestnut .57 B A B B Laurel .56 B B C B Northern red .56 B A B B Nuttall — B A B B Pin .58 B A C B Scarlet .60 B A B B Shumard — B A B B Southern red .52 B A B B Water .56 B B C B Willow .56 B B C B Oak, white Bur .58 B B B B Chinkapin — B B C B Delta post .60 B A B B Durand — B A B B Live .81 C B C B Oregon white .64 C B C B Overcup .57 B B C B Post .60 B B C B Swamp chestnut .60 B A B B Swamp white .64 B A B B White .60 B A B B Ohia 0.70 B B C B Persimmon, common .64 C A-B C B Sassafras .42 C B C B Silk-oak .51 B A B B Sugarberry .47 B B C A Sweetgum .46 B B B A Sweetbay .42 B C A A Sycamore, American .46 B A B A Tanoak .58 B B C B Tupelo Black .46 B B B A Swamp .45 B B B A Water .46 B B B A Walnut, Black .51 B A B B Willow, Black .34 C B-C B B Yagrumo hembra .26 C C B-C B Yellow-poplar .40 B B A A

26 Table 6.—Specific gravity and suitability of some U.S, species for various veneer uses ^—continued

Relative suitability- Common Specific name gravity 2 Construction Decorative Inner plies of Container plywood face decorative veneer and veneer panels plywood

SOFTWOODS Cedar Alaska- .42 B B A A Atlantic white- .31 C B A A Eastern redcedar .44 C A B C Incense- .35 B-C B B B Northern white- .29 B-C B B B Port-Orford- .40 B B A A Western redcedar .37 A-B A B-C B Cypress Baldcypress .42 A-B A B A Pondcypress B A B A Douglas-ñr Coast .45 A B-C B A-B Interior north .45 A B-C B A-B Interior west .46 A B-C B A-B Fir Balsam .34 B-C C C A California red .36 A-B C B-C A Grand .35 A-B C B-C A Noble .37 A-B C B-C A Pacific silver .40 A-B C B-C A Shasta red .36 A-B C B-C A Subalpine .31 B-C C C A White .37 A-B C B-C A Hemlock Eastern .38 B-C C B-C A-B Mountain .43 B C B A Western .38 A-B C B A Juniper Alligator .50 C C C C Rocky Mountain .51 C C C C Western .51 C C C C Larch, Western .48 A B C B Pine Digger B-C C C B Eastern white .34 B-C A-B B A Jack .39 B-C C C B Jeffrey .37 B A B A Knobcone B-C C C A Limber .37 B-C C C A Loblolly .47 A C C B Lodgepole .38 B B C A Longleaf .54 A C C B Pitch .45 B-C C C B Pond .50 B C C B Ponderosa .38 B A B A Red .44 B B C A Sand .36 B-C C C B Shortleaf .46 A C C B Slash .56 A C C B Spruce .41 B-C C C B Sugar .35 B-C A B A Table-Mountain .49 B-C C C B Virginia .45 B-C C C B Western white .36 B A B A Whitebark .37 B-C C C A Redwood .38 A-B A C A

27 Table 6.—Specific gravity and suitability of some U.S. species for various veneer uses ^—continued

Relative suitability Common Specific name gravity 2 Construction Decorative Inner plies of Container plywood face decorative veneer and veneer panels plywood

SOFTWOODS—continued Spruce Black .38 B-C C C A Blue — B-C C C A Engelmann .33 B c c A Red .38 B c c A Sitka .37 A-B B B A White .37 B-C C C A Tamarack .49 A-B B C B Yew, Pacific .60 C A C B

1 Rating of A indicates species is well suited for end product; B, intermediate; and C, generally not well suited for this product. 2 Based on weight when ovendry and volume when green.

Table 7.—Specific gravity and suitability of some imported species for various veneer uses

Relative suitability ^ for Common name Specific gravity 2 Construction Decorative Inner plies of Container plywood face decorative veneer and veneer panels plywood Angélique 0.60 B B-C C B-C Apitong .59 A B B B Avodire .51 B A B B Brazil nut .56 B B B-C B Bubinga .65-.76 B A B-C B Caribbean pine .68 A-B C B-C B Cativo .40 B B A-B A Ceiba .25 C C A-B C Determa .51 C C C B-C Kapur .64 A-B B-C C A-B Keruing .46-.70 A-B B-C C A-B Klinki pine .38 B B A A Lauan .40-.46 B A B A-B Limba .49 B A-B B B Mahogany .45 B A A B Mengkulang .56 A-B B-C B-C B Meranti .36-.51 B A A B Mersawa .51 B B B B Muritinga .45-.60 B B-C B B Ocote pine .55 A C B-C B Okoume .37 B B A A Paldao .60 B A B-C B Primavera .39 B-C A B B Rosewood .80 B-C A B-C B-C Sapele .60 B A B A Teak .57 B A B B

1 Information primarily from "Properties of Imported Tropical Woods," by B. F. Kukachka, USDA Forest Serv. Res. Pap. FPL 125, 1970 and from "Veneer Species of the World," lUFRO Interim Report, 1976. 2 Specific gravity based on volume when green and weight when ovendry. 3 Rating of A indicates species is well suited for end product; B, intermediate; and C, generally not well suited for this product.

28 TECHNIQUES FOR PEELING, SLICING, AND DRYING VENEER

From a given supply of logs, the processor sign of debarkers, lathes, slicers, veneer con- can improve the quality of veneer in two gen- veyors, clippers, and dryers. All of this equip- eral ways: Handle the wood so that variability ment must be properly maintained, set up, and is minimized, and carefully select and ade- operated to consistently produce good-quality quately maintain processing equipment. veneer. Handling the wood to minimize variability The veneer processing techniques described involves such things as log storage, breaking in this bulletin follow the chronological steps logs into bolts or flitches, and heating or cooling in which they occur from log to dry veneer. the wood prior to cutting. This is followed by a section on quality control Processing equipment involves the basic de- and trouble shooting to minimize veneer defects.

LOG STORAGE Veneer logs can be kept in good condition for The sapwood of many species is subject to some time providing the storage conditions are attack by anaerobic bacteria even though the suitable. With poor storage conditions, logs can wood is kept wet. This has caused objectionable deteriorate by drying and cracking of the log odor, particularly in tropical hardwoods like ends and other exposed wood; development of muritinga, ceiba, and cativo. Bacteria may also blue stain, decay, and oxidation stain ; attack by cause excessive porosity in pines like ponderosa insects; cracks and grain separation due to and the southern species. The best way to con- freezing and thawing; development of undesir- trol bacterial action is processing felled trees able odor ; and increased porosity due to attack within 1 month or by storing the wood below by bacteria. 40° F. (5° C). Spraying with chemicals may End drying and splits in logs can occur with help, providing the bacteria has not already en- susceptible species like dense hardwoods in one tered the wood. hot, dry, windy day when the sunlight falls Given these many possible problems, what is directly on the log end. End drying is less of a the best procedure for log storage? In general, problem with a species like Douglas-fir stored veneer log storage should be kept to a minimum. in winter in the damp Northwest. Blue stain The first logs into storage should be the first and mold can occur in a week to 10 days on the ones out of storage for processing. Ideal storage sapwood of species like sweetgum and southern conditions would be to end coat and keep the pine stored in humid summer weather in the bark intact on tree-length logs that are either South. Decay generally requires weeks or held at high humidity and a temperature just months to develop. Oxidation stain, which low- above freezing (34° F or 1° C) or completely ers the value of white sapwood of species like submerged in cold water (34° to 40° or 1° to birch and maple, may occur through the ends 5° C). The next best system would be to keep of unprotected logs stored several weeks during the logs under a roof and all surfaces constantly summer. wet by a water spray. This would be just as Insects like lyctus beetles may attack a log good as the first method, providing the tempera- within hours after felling. To minimize insect ture was between 34° and 40° F (1° to 5° C). attack, logs stored in warm weather should be used within 2 weeks after felling, treated with A common storage method that is generally an approved chemical,^ or stored under water. satisfactory is to keep all log surfaces wet with Freezing and thawing of logs of species such a water spray but without using a roof. When as sweetgum and claro walnut may fracture the water spray is not feasible, then a chemical wood so that it is useless for veneer. This is spray and end coating may permit satisfactory less of a problem with species grown in north- storage. Less desirable methods which are some- ern climates. times suitable include floating the logs in a pond and cold-decking the logs. A much more 3 Check with the local County Agricultural Agent or State Agricultural Experinment Station for approved complete discussion of log storage is given by recommendations. Scheffer (60).

29 BARK REMOVAL The subject of bark removal is one in which veying the material from a mechanical de- two people, both knowledgeable in the field, may barker, as bark may come off in large sheets. disagree. The reason is the wide variability in In general, softwoods like pine are easier to difficulty of removing bark. Three factors that debark than hardwoods like hickory, but there must be considered are: (1) variability of bark are many exceptions. For example, fall-cut east- adhesion within a species; (2) variability of ern hemlock is reported to be more difficult to bark adhesion between species; and (3) type of debark than northern hardwoods like maple and equipment used for debarking. birch. Other examples of softwoods that are difficult to debark are cypress with a fluted base, Variability Within a Given Species western redcedar with stringy bark, and red- wood with very thick bark. The difficulty of Spring-cut logs are easier to debark than fall- bark removal of species that grow in the United cut logs of the same species. This general state- States is shown in Appendix IV. ment is true for all species. Actual measure- ments of the wood-to-bark bond on several Types of Equipment Used species indicate that this increase of bond strength from spring to fall may be 100 to 200 Different systems have been used for debark- percent. ing veneer logs, including hand tools, bark A second factor is the temperature of the saws, water under high pressure, flailing chains, wood and bark at the time of bark removal. and drum debarkers. Some mills have used an Heated wood is much easier to debark. When old lathe to debark and round bolts. At present, veneer logs were commonly debarked by hand, however, two methods are by far the most com- a main reason for heating the logs was to make mon for debarking veneer logs—^the cambio- bark removal easier. Frozen logs are particu- shear or ring debarker, and the rosser-head larly difficult to debark. A plant may even install debarker. Combination machines may use either a hot pond to get logs above freezing so they cambio-shear or rosser-head or both. can be more readily debarked with a mechanical Some factors to consider in choosing a de- debarker. barker, besides the original and operational Another factor in debarking is whether or not costs, include species to be debarked, volume of the bark has been allowed to dry on the log. wood to be debarked, maximum and minimum Assuming no bacterial action has taken place, diameter of logs to be debarked, importance of the bark generally adheres more tightly after it fiber loss, pollution, ease of operation, and ease has partially dried. of maintenance. A fourth factor is the action of bacteria. Logs In general, the rosser-head debarker has a stored in a warm pond or under a sprinkler dur- lower initial cost, lower maintenance cost, is ing summer may be subject to attack by bac- easier to adjust, and is more adaptable for logs teria. Bacteria seem to prefer the inner bark as of a wide range of diameters. The rosser-head a food source. Consequently, logs stored in a is generally preferred for debarking rough logs pond and attacked by bacteria may have the of species like hickory, logs that vary widely in bark loosened so that it will come off in one big diameter, and logs that may be frozen. sheet. Such a big piece may jam the bark con- The cambio-shear or ring debarkers are gen- veyor. Conversely, bacteria attack may make erally preferred by plants processing logs with peeling of bark much easier when using hand relatively uniform diameters and where high tools. production and low fiber loss are important. A typical installation would be in a large southern Species Differences pine plywood plant. Individual wood species differ in strength of Several manufacturers of cambio-shear de- the bond between the bark and the wood. In one barkers state that, by proper adjustment of tool study of fall-cut logs, the bark-to-wood bond pressure and feed, their equipment can debark of quaking aspen was more than 40 percent any species under any conditions, including stronger than that of red spruce. frozen logs. Similarly, manufacturers of rosser- Some species like basswood and elm have head debarkers state their equipment can be stringy bark. This becomes a problem in con- used to debark any species under any conditions.

30 SAWING INTO BOLTS OR FLITCHES It is generally desirable to harvest logs in as for flitches is generally to buck to length, then long lengths as possible and to saw into bolts or saw the flitches, and finally heat the flitches. flitches at the veneer-cutting plant. The reasons As flitches are generally a step in producing for doing this include less waste from end dry- face veneer, bark indicators are important for ing of the logs, a better opportunity to observe cutting logs to length and for producing the all sides of the log before cutting, availability flitches. Most or all of the bark is removed in of skilled labor trained to buck and saw flitches sawing and so does not significantly retard heat- from the logs for the best use, and better me- ing. The heated flitches are cleaned and any re- chanical equipment for handling and sawing the maining bark removed with a flitch planer just logs. prior to slicing. The sequences of debarking, bucking into bolts, and heating depends on type of logs, de- Saws Used in Processing Logs to Bolts barking and sawing equipment at the plant, and and Flitches whether log end splitting is a factor during Logs are cut to length of bolts or flitches pri- heating. In general, debarking reduces heating marily with large circular saws or with chain time, as bark is a good insulator. Heating in saws. In both cases it is important that the log long lengths reduces waste due to log end splits. and saw be positioned so the cut is at a right On the other hand, bark indicators of hidden angle to the axis of the log. defects in the logs may help the sawyer decide Logs are generally sawn into flitches with a where to break the logs for best grade. The bark handsaw or a circular saw. The vertically mov- may also protect the logs during handling. able circular saw that is mounted over the log A method sometimes used with hardwoods carriage permits sawing logs into thirds as well that tend to end split is to debark in long log as halves and quarters. In all cases it is impor- lengths, heat in long log lengths, and then buck tant that the log can be accurately positioned into bolts just prior to cutting veneer. This with respect to the sawline and that the sawyer method reduces the time required to heat the can see both ends of the log. If both lumber bolt by eliminating insulation by the bark. Log and veneer flitches are to be produced, the band- end splits are confined largely to the ends of saw may be advantageous, as generally a the long log and minimized at bolt ends exposed smaller saw kerf is produced. by crosscutting after heating. The process re- quires a continuous debarker, long heating vats, and equipment to handle long logs. Other dis- What Does the Sawyer Look For? advantages are that the bark indicators of de- Bolts fects are lost before bucking, and care must be Factors to be considered in bolts are sweep in used to prevent the debarked logs from picking the log, end trim, presence of large defects like up grit during handling. knots, and the length of the bolts required. If A method used with softwoods like southern possible, sweep in the log should be minimized pine is to debark in long log lengths, crosscut as it results in excessive roundup and short bolts, and then heat prior to peeling. This re- grain in the veneer. Thus, even though long quires a continuous debarker but permits heat- bolts are generally more valuable than short ing vats and handling equipment which work bolts, a log with excessive sweep would prob- with 8-foot and shorter blocks. It is a satisfac- ably be more valuable if cut into two or more tory method if end splitting is not a serious bolts to minimize the sweep. Logs that have problem and the handling equipment is kept been end coated or that have dried and checked clean so the debarked logs do not pick up grit. should be end trimmed. The cut should be at a Large-diameter logs such as old-growth right angle to the longitudinal axis of the bolt. Douglas-fir are sometimes cut to bolt length in Crosscutting with a hand-held saw can result in a pond, debarked in a machine designed for irregular bolt ends, which in turn can reduce 8-foot lengths, and then heated or cut at room the surface engaged by the lathe chucks and temperature. also cause the veneer to vary in length or re- The debarking-sawing-heating sequence used quire excess spurring at the lathe.

31 Flitches band veneer. Slicing and stay-log cutting is done primarily to produce decorative face veneer. A A log with sweep should be sawn into flitches stay-log is an attachment for a veneer lathe on so the sweep is perpendicular to the plane of which flitches may be mounted for cutting into the knife used in slicing. This permits full- half-round, back-cut, or rift veneer. Very high- length veneers from the start of slicing. A large quality core and crossband veneer is occasionally split or frost crack in a log may be minimized produced by quarter-slicing. Small, fast slicers by dividing a log along this longitudinal plane. have been used to produce container veneer. If possible, knots or other defects indicated in the bark should be trimmed out or be put at one Rotary edge or end of the flitch so the defect will occur Eighty to 90 percent of all veneer is cut at the edge or end of the veneer. In general, it by the rotary method (fig. 11-A). The rotary is desirable to saw the flitch parallel to the bark method gives the maximum yield; it results in and take the taper from the center of the log. the widest sheets; knots are cut to show the This makes for straighter grain and a balanced smallest cross-section; and most juvenile wood design in the face veneer. The side of the flitch and splits are left in the core. Some rotary-cut that is to be the exit side for the knife at the veneer is used for the decorative eflfect of an- end of the cut should be sloped, with the wide nual rings or irregular grain, such as that side next to the flitch table to minimize tear-off causing "blister'' figure. during slicing. The top and bottom of the back of the flitch should be squared so the slicer dogs Flat-Slicing and Half-Round Cutting can obtain a good grip. The recent develop- Flat slicing (fig. 11-F) is done on a slicer, ments of remotely controlled extension dogs and and half-round cutting (fig. 11-B, C) is done on a fixture for holding the flitch by vacuum make a lathe. Half-round cutting may be done with this precaution less important. flitches mounted on a stay-log (fig. 11-C), or by Frequently the sawyer preparing flitches for chucking a bolt at one edge rather than at the face veneer has the option of sawing the log for center, and by having the lathe chucks mounted lumber. This judgment is generally made after eccentrically (fig. 11-B). Veneers produced by he has sawn through the pith and can see the the flat-slicing and by half-round cutting are quality and figure in the wood. If the log has similar in appearance. The centers of the sheets some limitation for slicing, such as ring shake, are essentially flat-grain while the edges are it may still be possible to recover high-quality rift or even quartered material. The half-round lumber. method gives slightly wider sheets and a bigger area of flat cutting in the center of the sheet Choice of Cutting Direction than the flat-slicing method. These two cutting Some of the ways bolts or flitches are pre- methods show growth rings to advantage. When pared and cut into veneer on a lathe or a slicer the grain dips in and out of the sheet, the figure are illustrated in figure 11. is broadly termed ''crossfire.'* Burls are gen- There are two main directions in which erally cut by the half-round method and crotches veneer can be cut—parallel to the annual rings by the flat-sliced method. (rotary-cut) or parallel to the wood rays (quar- ter sliced). The other methods fall between Rift-Cut these two extremes. Half-round, flat-slicing, A quarter section of a log is cut and mounted and back-cutting all result in cutting parallel to so that the knife cuts about a 45° angle to the the rings in the center of the veneer and at wood rays. This can be done with a stay-log on angles to the rings at the two edges of the veneer a lathe (fig. 11-E) or on the slicer (fig. 11-H). sheets. Rift-slicing is a deliberate attempt to The method is used primarily with white oak to cut midway between parallel to the rays and produce a figure caused by the wood rays. When perpendicular to them. the veneer is coarse-textured and the annual The lathe is used to cut practically all veneer rings are not exactly parallel to the edge of the used in construction plywood, some decorative veneer, the figure is called rift-cut. A form of face veneer, and most container, core, and cross- rift-cut that is particularly desirable is comb

32 LATHE S LI CE R

A, ROTARY (YELLOW BIRCH) F. FLAT SLICED (WALNUT)

B, ONE'HALF ROUND (RED OAK) 6. OUARTER SLICED (PRIMAVERA)

C. ONE-HALF ROUND (BLACK CHERRY) H. RIFT SLICED (WHITE OAK)

D, BACK CUT (ROSEWOOD) I. WHOLE LOG (FLAT SLICED) (ASPEN)

E, RIFT CUT (WHITE OAK) J. 1. FLAT SLICED 2. BACK CUT 3, OUARTER SLICED M 140 660 Figure 11.—Some of the cutting directions used to obtain different grain patterns in veneer. The species in paren- theses are typical of those cut by the method diagramed. The wide dark lines under ''slicer" represent the back- board left at the end of slicing.

33 grain. By contrast with the more familiar form, able than the sapwood. Rosewood is an example comb grain has fine texture, straight grain, and of this. no broad flakes. Sawn Quarter-Sliced At one time sawing was a common method of Quarter-slicing (fig. 11-G) produces straight, producing veneer, but it is almost obsolete be- narrow stripes in straight-grained softwoods cause of the large volume of material lost as like Douglas-fir, redwood, and western redcedar sawdust. Sawing does have the advantage that or straight-grained hardwoods like oak and wal- it is not necessary to heat the log or flitch prior nut. Quarter-slicing is also done with species to cutting, the two sides of the veneer are essen- having interlocked grain such as mahogany and tially the same in quality, and thicker veneers primavera. This produces a plain stripe or can be produced without developing cracks into ribbon-grain which reflects light in different the veneer. An example where these advantages directions depending upon the position of the are important would be the top or back of a viewer. Plain-stripe is a comparatively broad musical instrument, such as the guitar. Species stripe and not too pronounced. A ribbon stripe like spruce, oak, cypress, and eastern redcedar has narrower bands and is more highly reflec- are occasionally sawn. Sawn material can be tive. When the grain in the wood dips in and flat-cut, quarter-cut, or rift-cut much the same out of the sheet, the figure is called a broken as when slicing with a knife. stripe. Figure in Veneer Back-Cut As briefly described under the different cut- Back-cutting (fig. 11-D) is done on a lathe ting directions, the appearance of veneer can be with a stay-log, much like half-round cutting, greatly affected by whether the veneer is cut However, instead of cutting from the sapwood tangential to the annual rings, at a right angle side, the cut is from pith side of the flitch. to the annual rings, or somewhere in between. Back-cutting is uncommon and is done where Figures 12 to 15 are examples of the appear- the heartwood is narrow and much more valu- ance of face veneer.

CONDITIONING WOOD PRIOR TO CUTTING VENEER The moisture content, permeability, and the Wood Permeability temperature of wood can have a marked effect The more permeable wood is to water, the on veneer cutting. easier it is to cut. But permeability is also largely inherent in the species. Sapwood of Wood Moisture Content some species can be made more permeable by storing in a warm, wet condition so bacteria Poor cutting results if nearly all cell cavities will attack it. This may make it easier to cut in the wood are filled with water or if the mois- into veneer but it may also affect the odor of the ture content is below the fiber saturation point wood and its gluing properties. These disadvan- (about 30 percent for all species). Unfortu- tages make it unlikely industry will purposely nately, there is little the plant manager can do induce bacterial attack to improve cutting. to drastically change the moisture content in a bolt or flitch. Rapid processing, storage under Wood Temperature water, or a sprinkler system will prevent green logs from drying. Logs having very high mois- The major factor under control of the plant ture content cannot be partially dried quickly manager is the temperature of the wood when without developing degrade at the outer por- it is cut. This is an area where strong differ- tions of the log. Steaming may slightly reduce ences of opinion exist among veneer plant man- the time required to dry the veneer. agers. For example, a hardwood plant manager

34 M 139 946 M 139 948 Figure 12.—Rotary-cut yellow birch with the figure Figure 13.—Flat- or plain-sliced black walnut with fig- caused by annual rings. ure from the annual rings and also a dip in the grain. The dip in the grain is sometimes called cross figures. in Wisconsin stated that the entire quality con- Before commenting on these statements, let's trol in his plant hinged on proper heating of examine some of the known effects of heating bolts prior to cutting veneer. He stated that on green wood. many things depend on whether or not the bolts are properly heated: Smoothness, tightness, Some Effects of Heating on Green Wood and thickness control when cutting the veneer; buckle, splits, and uniform moisture content Plasticity after drying; and quality of glue bonds. Heating green wood makes it more plastic. In contrast, a softwood plant manager in This fact is easily demonstrated with mechan- Oregon stated that heating of veneer bolts was ical tests and is the basis of steam bending of not worth the cost and he did not want log heat- wood. Within the limits used in veneer produc- ing equipment in a plant that was to be built. tion, plasticity is not time-dependent; as soon

35 ! '

1.il f.

M 139 945 Figure 14.—Rift-sliced white oali. The pencil stripe fig- Figure 15.—Quarter-sliced primavera. The broken stripe ure is caused by cutting the wood rays at an angle of figure is caused by interlocked grain which dips in and about 45°. out of the sheet. as green wood reaches a given temperature, it Hardness is as plastic as it will get at that temperature. Heating wet wood makes it softer. Hard Veneer cut from heated bolts or flitches can be knots, which if unheated may nick a sharp bent with fewer fractures than veneer cut from knife, will often be softened by heating so they unheated wood. This effect is more noticeable can be cut. Heat also softens pitch but does not with dense species and when cutting thick soften mineral deposits like calcium carbonate veneer. If a plant is interested in cutting tight, and silica. thick veneer from dense species, then heating While heating generally aids cutting of dense of the bolts or flitches is an important part of species, it may oversoften less dense species and the process. result in tearing of fibers and a fuzzy surface

36 on the veneer. This phenomenon occurs at differ- steel strap 1 inch (25.4 mm) wide applied by a ent temperatures for different species. In gen- tool commonly used to strap containers was in- eral, if the wood cuts with a fuzzy surface, it is effective in preventing splits at the bolt ends too hot. during heating of Brazil nut about 2 feet (0.6 m) in diameter. End splits were reduced Dimensional Changes in another bolt of Brazil nut heated to 160° F When green wood is heated, it expands tan- (71° C) by wrapping the ends with i/i>-inch gentially and shrinks radially. This fact has (12.7 mm cable and applying a tensile force of been verified for both softwoods and hardwoods 40,000 pounds (18,000 kg) to the cable. Similar by a number of researchers. The amount of results have been obtained experimentally with shrinking and swelling varies with the species. red oak. This thermal movement increases with tem- Steel strapping is used on the ends of flitches perature but the rate of increase is slow up to by some face veneer plants. Plant managers re- about 150° F (66° C) and then increases more port this reduces splitting. As indicated earlier, rapidly. Consequently, if a species tends to the forces that tend to cause end splits during develop splits through the pith and shake due to heating are less in flitches than in bolts of the heating, a general recommendation is to not same species. heat above 150° F. Tangential expansion and radial shrinkage Color Changes can occur in flitches without causing end checks Heating green logs may darken or lighten the or shake. It is, therefore, often possible to use wood. Heating in steam is reported to change higher heating temperatures with flitches that color more than heating in water. The color do not contain the pith than with bolts that do changes may be desirable or undesirable. In contain the pith. general, heating tends to darken sapwood of all species. Similarly, the heartwood of oak, beech, Growth Stresses and Port-Orf ord-cedar are darkened by heating. When bolts with large growth stresses are To keep the wood as light in color as possible, heated, the wood at the bolt ends is temporarily minimum heating times and temperatures are weakened in tension perpendicular to the grain ; recommended for ash, oak, maple, and beech. the growth stresses, together with dimensional Heating may also affect later color changes. changes discussed earlier, may cause star-shaped Wet sapwood of yellow birch may develop cracks radiating from the pith at the end of the orange streaks, thought to be an oxidation stain bolts. promoted by enzymes. Adequate log heating The longitudinal growth stresses act pri- tends to inactivate the enzymes and reduce the marily at the two log ends. When the wood is likelihood of this undesirable orange stain oc- heated to a temperature of 180° F (82° C), or curring. Similarly, adequate heating of oak sap- higher, 90 percent or more of the growth wood reduces the development of gray-brown stresses are relieved. If the wood is heated in oxidation stain. long log lengths and then crosscut to bolt Warm, wet walnut veneer is often held in lengths, the newly formed bolt ends will have storage until the sapwood becomes darker from less end splits than would develop if the bolts oxidation stain and the heartwood reaches a were cut to length prior to heating. desirable light gray-brown color. It is then Longitudinal growth stresses tend to cause dried to minimize further color changes. flitches to bow toward the bark side. This bow may become worse during heating. Bowing can Strength of Wood be reduced by strapping the flitches together Occasionally a question is raised about with the bark side out and allowing the heat to whether heating bolts or flitches prior to cut- relieve the growth stresses while the flitches are ting veneer weakens the dry veneer. As dis- mechanically held flat. A wide, strong strap or cussed earlier, heating wet wood plasticizes and heavy chains and bolts must be used as the softens it while it is hot. After drying, the wood forces involved are large. cut from heated veneer bolts or flitches has Experimental strapping has also been tried much the same strength as wood cut from un- to reduce end splits in bolts during heating. A heated controls.

37 However, excessively long heating* and high 60° F (16° C) shrank 13.3 percent, while temperatures can reduce the strength perma- matched veneer peeled at 135° F (57° C) shrank nently. For example, Douglas-fir and sitka 15.1 percent. The effect was greater the higher spruce heated for 50 days at 150° F (66° C) in the conditioning temperature and the longer water lost 10 percent of the modulus of rupture the heating time. of unheated controls. When the same species Drying Time were heated at 200° F (93° C), the modulus of rupture was reduced about 10 percent in ap- When sound, green logs with a high moisture proximately 10 to 12 days. Modulus of elasticity content are heated in hot water or steam to (stiffness) values were affected even less by 150° F (66° C) or higher, they generally lose heating. 1 to 10 percent of the moisture in the log. This Heating has a greater effect on hardwoods is believed to be caused by air in the cell cavi- than on softwoods. In contrast to the 10 to 12 ties expanding and pushing out free water. days of heating required for the softwoods, Decayed logs may pick up water during heating Douglas-fir and sitka spruce, to lose 10 percent in water. in modulus of rupture, it took only 6 to 7 days It is sometimes thought that warm veneer of heating for a comparable loss in yellow birch. cut from heated wood will dry faster than veneer cut from bolts or flitches that are not Torque to Turn Bolts heated. Grantham and Atherton (25) report The torque required to turn a bolt into veneer that Douglas-fir sapwood cut from bolts at depends on wood density, veneer thickness, bolt about 140° F (60° C) dried 10 percent faster diameter, setting of the knife and pressure bar, than sapwood from unheated bolts. They found and wood temperature. In one test, we found the drying time for Douglas-fir heartwood was that 1/4-inch (6.35 mm) basswood veneer cut at the same for veneer cut from heated and un- 200° F (93° C) required 42 percent less torque heated bolts. Thin veneer cut from hardwoods than matched material cut at 35° F (2° C). generally requires the same drying time However, the torque that the bolt end would whether the bolts or flitches are heated or not. accept at 200° F (93° C) was 44 percent less These results are to be expected from the rela- than matched material at 35° F (2° C). In tively small amount of energy required to heat other words, heating reduced the cutting force wood compared to the large amount of energy about as much as it reduced the wood's ability required to dry it. to resist spin-out. Warp Bolt heating is sometimes blamed for spin- out, or turning of the chucks in the bolt ends. Veneer cut from heated wood is generally This can happen if bolts are heated at a high tighter than veneer cut from unheated wood. temperature for a short time. The bolt ends are Tight-cut rotary veneer may tend to reassume then hot and soft, while the inner part of the the curvature of the bolt more than loosely cut bolt is cooler and requires a relatively higher veneer. The tendency of the veneer to curl is force for cutting. The better procedure is to also related to the setting of the pressure bar heat the bolts at a lower temperature long during cutting. enough so each bolt is uniformly hot. This pro- If the logs or flitches are heated and then cedure also minimizes splits at the bolt ends cooled in water, the end grain will pick up that may contribute to break-out of the bolts water. If the veneer is not spurred at the lathe, during rotary cutting. this extra water at the ends may affect drying at the ends of the sheets. Shrinkage Heating of softwood veneer bolts or flitches Decay Resistance of Naturally Durable Woods has no detectable eflfect on the shrinkage of The heartwood of green Douglas-fir, Alaska- veneer cut from them. In contrast, heating cedar, white oak, and true mahogany was bolts or flitches of some collapse-susceptible heated at 212° F (100° C) for various times hardwoods may result in noticeably higher from 1 to 48 hours. After 12 hours of heating, shrinkage of veneer cut from the preheated the white oak and mahogany were slightly less wood. In one trial, alpine ash veneer peeled at resistant to decay than similar but unheated

38 logs. The Douglas-fir and Alaska-cedar were not Conclusions Related to Wood Temperature noticeably affected. After 48 hours at 212° F The improved veneer tightness, smoothness, (100° C), all of the woods were slightly less and color are sufficiently beneficial so that decay resistant than the unheated controls of almost all producers of hardwood face veneer the same species. The results indicate the heat- heat bolts or flitches prior to cutting veneer. ing of wood in normal veneer processing does Whether heating has a significant effect on not degrade decay resistance from a practical veneer thickness, moisture content after drying, point of view. and quality of glue bonds is not well docu- mented. The Wisconsin plant manager was, Conclusions on Some Effects of Heating nevertheless, correct when he stated that heat- Some Benefits ing must be done properly in order to produce high-quality hardwood face veneer. The most obvious effect of heating is that it makes it possible to cut tighter veneer than The softwood plant manager in Oregon who can be cut from unheated wood. Tighter cutting did not want heating equipment was producing means greater strength in tension perpendicu- a very different product. The panels from his lar to the grain of the veneer and so less split- plant were to be used mainly for construction ting of the veneer in handling and less checking such as sheathing. Here, properties of veneer of face veneer in service. A second effect of tightness, smoothness, and color are less im- heating is that it softens knots, thereby reduc- portant. Many western softwood plywood plants ing nicks in the lathe or slicer knife. The make satisfactory construction plywood from sharper knife in turn helps produce smooth unheated veneer bolts. However, research and veneer surfaces. Other possible benefits of heat- plant experience indicates that heating pays ing include less power to cut equally tight even for manufacture of construction plywood. veneer, improvement of color by decreasing This is particularly true if there is any danger oxidation stain in the sapwood, and reduced that the logs will freeze. Both researchers and veneer drying time. industrial veneer producers have found that it is not possible to cut veneer from frozen logs. Frozen wood cannot be cut satisfactorily into If the logs do freeze, then the plant without veneer with a knife. Wood bolts or flitches yield heating facilities will be shut down. veneer of varying quality with varying tem- perature. The changing temperature may ad- Another advantage of heating for this kind versely affect the lathe or slicer settings. of product is that the veneer is tighter cut and as a result a higher percentage of 4-foot-wide In general, heating is beneficial when slicing and 2-foot-wide sheets is produced. That is, less figured face veneer from dense species. Heating splitting occurs during handling of the green, is also important if tight veneer is to be pro- tightly cut veneer than when handling loosely duced in thicknesses of % inch or greater. cut veneer. In addition, heated knots are softer Some Disadvantages and result in less knife wear than cutting sim- ilar wood from unheated blocks. Grantham and Most disadvantages of heating can be attrib- Atherton (25) conclude that heating does pay uted to using too high a heating temperature when cutting veneer for plywood to be used in or too long a heating time. Overheating may construction. cause excessive end splits in bolts of species like oak, fuzzy surfaces on springwood and glossy surfaces on summerwood, shelling or separation on springwood and summerwood dur- Time Required to Heat Veneer Bolts ing cutting, unwanted darkening of the veneer, and Flitches increased spinout of bolts by softening the end Most investigators agree upon some points grain, or increased shrinkage. But the heating about the time required to heat veneer bolts temperature must be very high and the heating and flitches, but other points are controversial. time very long to affect the strength and dura- First, let us examine the points that are gen- bility of the wood. erally accepted.

39 Generally Accepted Points bient temperature. This is particularly true if logs of high moisture content may be frozen Uniform Final Temperature at some part of the year. While ice conducts The bolt or flitch should be heated long heat faster than water, the heat required to enough so that temperature of the wood from melt the ice can result in longer heating time the start of cutting to the end of cutting varies (11). When heating frozen wood of species with no more than 10° F (6° C). To achieve this a low moisture content like Douglas-fir heart- goal, the heating time must be sufficiently long wood, the heating times are shorter than for and the heating medium (steam or hot water) frozen logs with very high moisture content must circulate freely to all surfaces of bolts and like western hemlock. flitches. Effect of Grain Direction Effect of Diameter The time required to heat a large-diameter End grain heats about 2V2 times as fast as bolt or flitch is much longer than the time re- side grain. The rate of heating in the tangen- quired to heat one of small diameter and gen- tial and radial directions is about the same. erally increases with the square of the diameter. Because most flitches and bolts are long com- For example, while a bolt 1 foot (0.3 m) in pared to their cross sections, heating through diameter might be heated in 14 hours, a bolt of side grain generally is the controlling factor. the same species 2 feet (0.6 m) in diameter Faster end-grain heating probably means knots would require about 60 hours. This example is heat faster than surrounding clear wood. This from the report by Fleischer (20) for wood is fortunate as one of the reasons for heating having a specific gravity of 0.50, an initial wood is to make the knots soft enough so they will temperature of 60° F (16° C), a temperature of not turn the edge of the lathe or slicer knife. the water used to heat the bolt of 150° F (66° Variability of Heating C), and the final temperature at a 6-inch (15 The rate of heating the flitches, even of the cm) core of 140° F (60° C). The time required same species, is somewhat variable due to irreg- to heat nonfrozen logs increases approximately ular shapes, differences in specific gravity, and as the square of the log diameter (11). defects like cracks. Therefore, heating sched- Effect of Temperature Gradient ules cannot be precise. In general, the sched- The greater the difference in temperature be- ules should be developed for the largest bolts tween the wood and the heating medium, the or flitches that are to be heated, starting from faster the heating rate. As the wood approaches the lowest ambient temperatures in the log the temperature of the heating medium, the storage area. The most common problem in rate of heating becomes very slow. As a result, heating veneer logs is insufficient vat capacity when selecting heating schedules, it is generally to adequately heat the logs or flitches under all practical to aim for a core temperature 10° F operating conditions. (6° C) lower than the temperature of the heat- ing medium. Some veneer plants use an equaliz- Controversial Points ing period at the end of the heating cycle to Effect of Heating Medium take advantage of the faster heating with a MacLean (i6) reported that water heats large temperature gradient and still end up with wood 5 to 10 percent more slowly than steam. relatively uniform temperature throughout the He found the slowest rate of heating in air at block (25). A limitation to this practice is the bolt end splitting that may occur with the high low humidities, but the rate was increased as initial temperature. the humidity was increased. In contrast, Feihl (11) found that hot water heats as fast or Total Temperature Change Required faster than steam. Feihl points out that this The colder the wood, the longer the heating apparent conflict may be due to the experi- time required to bring it to the desired cutting mental conditions. MacLean was using steam temperature. In other words, the heating capac- at 212^ F (100° C) and higher, while Feihl ity of a plant should be figured for the worst used a steam-air mix at a temperature generally winter conditions rather than the average am- below 200° F (93° C).

40 Some commercial plants inject steam into a attributes it to either higher specific gravity of vat and at the same time spray hot water over the wood or higher moisture content in the log. the bolts or flitches. In addition to adding heat Log End Splits to the wood, the hot water spray prevents dry- ing and checking. Many veneer plant operators believe rapid A commercial modification of the steaming heating increases end splits. Meriluoto {Jf.8) re- hot-water spray method is to blow steam ports that heating frozen birch at less than 5° through an alkaline water solution. Salts added C (41° F) until the wood was above 0° C to water will raise the boiling point slightly. (32° F) resulted in less end splits than when These few degrees change in temperature would heating frozen bolts in water at 14° C (57° F). not seem to be important for conditioning A few trials at the U.S. Forest Products veneer logs. This would appear to be mildly Laboratory with nonfrozen bolts showed little alkaline because.we know strong alkali solu- difference between end splits in bolts heated tions will break down wood structure. However, slowly and matched bolts put directly into water in typical heating cycles, the alkali would not that was at the desired final temperature. While penetrate more than a fraction of an inch in slow heating may slightly reduce end splits, most wood species. the maximum heating temperature seems to be more important. The higher the heating tem- Effect of Differences in Moisture Content and perature, the larger the end splits. Specific Gravity MacLean H6) found wood that is well below Duration of Heating at Constant 30 percent moisture content heats more slowly Temperature than green wood, but differences in moisture Some researchers have reported that long- content above about 30 percent had no impor- time heating using a low temperature has the tant effect on the rate of heating. All veneer same effect in conditioning wood for cutting cutting, of course, is done with wood at a mois- veneer as shortime heating at a high tempera- ture content of 30 percent or higher. For prac- ture. Experiments at the Forest Products Lab- tical purposes, MacLean is suggesting that oratory in Madison indicate this is question- green wood of any given species will heat at able. Duration of heating up to several days about the same rate at any moisture content does not affect the plasticity and hardness of above 30 percent. the wood. This in turn means excessively long In contrast, he found that the rate of heat- heating periods do not improve the tightness ing of wood varied inversely with the specific or smoothness of the veneer compared to short- gravity {J^6), Although the heat conductivity term heating to the same final temperature. of wood increases with the increase in specific Heating longer than necessary to bring the gravity, the diffusivity (a measure of the rate wood to the desired cutting temperature may of temperature change) decreases as specific darken the wood and increase shrinkage. gravity increases. In other words, the lighter woods will heat to a given temperature more Conclusions on Time Required rapidly than the heavier woods, although the The most common difficulty in heating veneer heavier ones are better conductors of heat. bolts and flitches is insufficient vat capacity. Feihl {11) found that the rate of heating is The single largest factor in the required heat- related to the specific gravity of the total log ing time is the diameter of the bolt or flitch (that is, the wood and the water). He reported to be heated, with required heating time in- that sinker logs require longer heating time creasing directly with the square of the log than logs that float one-third out of water, and diameter. Good estimates of the required heat- that logs that float one-half out of water require ing time for unfrozen logs can be made from less time to heat than logs that float one-third Forest Products Laboratory Report No. 2149 out of water. (20). FeihFs report (11) can be used to esti- In general, Feihl and MacLean agree heavier mate the heating time for frozen and unfrozen logs require longer heating. wood. MacLean attributes the longer heating time A special heating cycle may be appropriate to higher specific gravity of the wood; Feihl if the color of the wood is important.

41 220

200

180

160

140

120 LEGEND: /—BASSWOOD 2-ASPEN, QUAKING 100- 3-COTTONWOOD, WESTERN 4-YELLOW - P'OPLAR 5- SWEETGUM 3 TUPELO 6-WALNUT, BLACK 80- - 7-BIRCH, YELLOW 8-MAPLE, SUGAR 9- OAK, NORTHERN RED 10-BEECH, AMERICAN 60- ~ II-OAK, WHITE 12 - HICKOR Y, SHA GBA RK

40V 0.30 0.35 O 40 0.45 0.50 0.55 0.60 0.65 SPECIFIC GRAVITY M 145 394 Figure 16.—Favorable temperature range (area between heavy lines) for cutting veneer of hardwood species of various specific gravities. Points show favorable temperatures for the individual hardwood species indicated. The data apply to the rotary cutting of veneer Vs inch thick, of straight-grained wood, free of defects such as knots or tension wood (''soft streaks").

42 Hot Water Versus Steam Heating chambers. With a good system it is possible to keep the temperature in the vat to within 2° Producers of hardwood face veneer generally to 4° (l"" to 2° C) of the desired temperature. prefer hot water vats while many softwood con- A system that works well with hot water struction plywood operations use steam cham- vats is to pump the water from one vat to an- bers. Recently heating- by hot water has become other. After heating one vat, the hot water is the preferred method for all types of veneer pumped to a second vat which has just been plants. loaded with unheated logs. The process is re- The rate of heating in the two systems is peated and the hot water goes from tank to about the same, assuming that both are prop- tank. Only enough heat is added to maintain erly operating. The actual temperature through- the temperature of the water. out the vat can be controlled more accurately Some mills strap a number of bolts or flitches with water than with a steam-air mix. End together so they can be handled as a bundle. drying is never a problem when heating in This practice is all right provided the flitches water vats, while it can be a problem in steam are separated by stickers to allow for circula- chambers if the relative humidity is not kept tion of the hot water to all wood surfaces. high. For workers, steam chambers are safer, as a fall into a hot water vat is generally fatal. Another method that has been used commer- In terms of manpower, one man with a lift cially is to move the bolts or flitches progres- truck can load and unload steam chambers for sively through a hot water or steam tunnel. a large plant while two or more men are gen- This practice has the merit of straight-line pro- erally needed to operate hot water vats. duction. To be successful, the bolts or flitches should be about the same diameter, the heat- ing time should be long enough to ensure heat- Heating Suggestions with Hot Water ing to the core of the bolts or center of the or Steam flitch, and the heating medium should circulate Debark logs prior to heating. so that all surfaces of the bolts or flitches are Heat in tree lengths or the maximum length heated the same amount. possible. The temperature at the core of larger bolts Segregate logs by diameter so the larger di- should be checked by drilling a hole in the mid- ameter logs can be given the needed longer dle of the core as it comes from the lathe. The heating time. hole should be 1 to 2 inches deep and just large Heat U.S. species at the temperature sug- enough to accept the thermometer. The ther- gested in Appendix IV. mometer should be inserted immediately and For unfamiliar hardwoods, use the heating the temperature recorded. temperature indicated for the specific gravity If the cores of the large-diameter bolts are of the wood (fig. 16). within 10° F (5° C) of the temperature in the The heating tanks should be arranged for vat, the smaller bolts will also be adequately circulation of steam or hot water so heat can heated. flow easily to all sides of the bolts or flitches. Steam should not impinge directly on the ends Proper heating will aid in producing tightly of logs, bolts, or flitches. cut veneer of uniform thickness. Underheating The temperature in the vats should be re- will result in less tight veneer and may result corded at half-hour or shorter intervals. Heat- in excessive handling splits and variation of ing should preferably be controlled by auto- veneer thicknesses. Overheating may cause matic valves on the steam lines, regulated by large end splits in the bolts, spin-out, fuzzy heat sensors in the heating chamber. veneer, and shelling of the grain. Temperature-sensing devices should be placed An example of the heating times required for in several locations in the vats or steam cham- bolts of different diameters is given below. bers. These in turn should automatically con- More detailed information and tables are given trol the heating of the water vats or steam in (11,20),

43 Examples : have hold-downs that will keep the logs under Heating time as related to bolt diameter.— water during heating. The doors on steam (Green 8-ft-long bolts with a specific gravity chests or covers on water vats should be tight of 0.50, an initial temperature of 70° F (21° and preferably be insulated. In many commer- C), water or air-steam vat temperature of 150° cial operations as much as heat is lost to the F (66° C) and a final temperature at a 6-in. atmosphere as is used to heat the wood. (15 cm) core of 140° F (60° C).) Bolt diameter Required heating Some Other Methods of Heating Veneer time Logs and Flitches (in.) (cm) (h) Some methods other than hot water or steam, 12 31.5 14 or steam-air mixtures below 212° F, have been 24 63 60 used on a small scale commercially or tried in Heating time as related to final core tempera- the laboratory. These include heating in steam ture,— (Green 8-ft-long bolts with a specific under pressure, electrically heating the wood, gravity of 0.50, an initial temperature of 70° F and forcing hot water or steam longitudinally (21° C), water or air-steam vat temperature through the wood. at 150° F (66° C), and various final tempera- tures at a 6-in. (15 cm) core.) Heating in Steam Under Pressure Final Required A few veneer mills heat veneer bolts in steam Bolt core heating under pressure. This shortens the heating time diameter temperature time as there is a bigger differential between the (in.) (cm) (°F) (°C) (h) starting temperature of the wood and the tem- 24 63 140 60 60 perature of the heating medium. However, 24 63 120 49 34 there is no special change at a temperature of 24 63 100 38 22 212° F (100° C). In going from 210° to 220° F (99° to 104° C) the reduction in heating time Heating time as related to initial ivood tem- is comparable to the time in going from 200° perature.— (Eight-ft-long bolts with a specific to 210° F (94° to 99° C). The disadvantages gravity of 0.56, a green moisture content of of a short heating cycle in steam under pressure 80 pet, various initial temperatures, water or include the very large temperature gradient air-steam vat temperature of 150° F (55° C), from the surface to the core of the bolts and and final temperatures at 4-in. (10 cm) core of excessive bolt end splits. 140° F (60° C).) Initial Required Electric Heating Bolt wood heating Electrical methods have been used experi- diameter temperature time mentally to heat bolts or flitches in an attempt (in.) (cm) (°F) (°C) (h) to reduce the heating time required with water 12 31.5 0-18 27 or steam. 12 31.5 40 4 21 In one set of experiments, electrodes were 12 31.5 70 21 16 placed at each end of a bolt or flitch and an electrical current sent through the wood by as Construction of Steam and Hot Water Vats high as 5,000 volts. Because the wood acted as Most heating vats or stegm chambers are a resistor, it was heated. This method is fast made from reinforced concrete. The vats should but has not been accepted commercially due to be constructed so that good circulation of the nonuniform heating. The electrical current fol- heating medium can be attained. The steam lows the path of the least resistance, which may pipes should not be placed so live steam will be wet streaks, cracks, or mineral streaks in impinge directly on the logs ends. Steam blow- the wood. These areas overheat and the other ing directly on the log ends overheats them parts of the bolt or flitch are underheated. and accentuates log end splits. If logs that float High frequency has also been used experi- are to be heated in hot water, the tanks should mentally to heat veneer bolts. High frequency

44 tends to overheat the wetter parts of the wood, inally through the wood structure (35). The and is much more expensive than heating in experimenters report that heating time was re- steam or water. duced to minutes and that satisfactory veneer was cut from bolts heated this way. The Forcing Hot Water or Steam method requires that the wood be permeable Longitudinally Through Wood and that a cap be attached to each bolt. Short beech veneer bolts have been heated experimentally by forcing hot water longitud-

VENEER CUTTING EQUIPMENT In selecting veneer cutting equipment, it is wear plates and mechanisms for taking up slack important to remember the forces involved in or play when it occurs. cutting. In one rotary-cutting study (^5), cal- Similarly, it is desirable to have hydraulically culated loads were as high as 200 pounds per operated dogs on slicers and hydraulically oper- inch of knife and 500 pounds per inch of pres- ated chucks on a lathe. Any tendency of the sure bar. Pictures comparing early lathes and wood work piece to come loose in cutting is modern lathes indicate that experience has dic- automatically corrected as hydraulic pressure tated the desirability of more rigid lathes. A resets the dogs or chucks. lathe or slicer operator never has trouble be- Another source of unwanted movement of the cause the equipment is too rigid, but excessive lathe or slicer is heat distortion. The use of movement of machine parts is a common prob- A-frames with screw takeups on the nosebar lem. If smooth, tight veneer of uniform thick- casting is one method of correcting for this. ness is to be produced, it is better to have a Another desirable feature is a means of keep- lathe or slicer that is stronger than necessary ing the lathe or slicer at a uniform temperature rather than to have one that is underdesigned. during setup of the knife and pressure bar and Some face veneer slicers are made so exces- during cutting. An added benefit is the reduc- sive pressure cannot be applied to the flitch. tion of blue stain caused by the reaction of iron The knife and bar carriage is not fastened on or steel with wet wood. Keeping the knife and the ways of some horizontal slicers. Thus, if pressure bar warm reduces condensation and so the total force against the flitch exceeds the reduces the staining. weight of the knife and pressure bar carriage, The heart of any lathe or slicer is the knife the carriage is lifted from the ways. Similarly, and pressure bar. The machine should permit on vertical slicers, the knife and bar assembly rapid change of the knife and bar and easy ad- is not held on the half-bearings that allow the justment of the clearance angle of the knife knife to be offset on the upstroke of the flitch and the lead and gap between the knife and table. If there is excessive nosebar pressure, nosebar. If these adjustments are diflScult to thin veneer sheets are produced and eventually make, the operator will make as few adjust- the flitch will not clear on the upstroke. At this ments as practical. Consequently, the machine time, the knife and bar carriage will be lifted will produce poorer quality veneer than would slightly from the half-bearing. When the car- be produced on easily adjustable equipment. riage falls back, the noise alerts the slicer op- erator that he has too much nosebar pressure. Retractable dogs on slicers and retractable chucks on lathes permit secure holding of large There is no mechanism such as this for wood flitches and bolts; when the dogs or lathes. Excessive nosebar pressure can progres- chucks are retracted they permit continuous sively build up until the bolt spins out of the chucks, the motor stalls, or some part of the cutting to thin backboards or small-diameter lathe breaks. cores. Any moving part on a lathe or slicer is sub- Recent development of the vacuum table per- ject to wear. Consequently, preloaded antifric- mits fast loading of flitches and cutting to a tion bearings are a good investment as well as thin backboard. However, the flitch back should

45 be wide, flat, and smooth to maximize the hold- Cutting Action on Lathe and Slicer ing power of the vacuum table. The lathe drive is often a separate item al- Similarities of Lathe and Slicer lowing the purchaser to specify the type de- The knife and pressure bar are very similar sired. Some options include a steam engine, a.c. on both the lathe and slicer and perform the motor with a speed changer, d.c. motor with a same function. Cross sections of a lathe (fig. motor-generator set, and hydraulic motor. In 17) and slicer (fig. 18) illustrate the position all cases it is desirable to be able to increase of the knife and bar in the two machines. Ter- spindle speed as the block diameter decreases minology used to describe the knife and pres- to keep the cutting speed constant. Hancock and sure bar on lathes and slicer is shown in figure Hailey (26) describe lathe drives in some detail. 19. The knife severs the veneer from the bolt or flitch. The knife bevel angle is about the same for knives on a lathe or slicer. The knife used on a lathe may be slightly more hollow ground.

BOLT

CHUCK

KNIFE ANGLE

M 140 657 Figure 17.—Cross section of a veneer lathe having a fixed pressure bar.

46 M 140 656 Figure 18.—Cross section of a vertically operating veneer slicer.

The pressure bar on both the lathe and slicer Continuous cutting is advantageous because it compresses the wood, with maximum compres- means more production with a given cutting sion ideally occurring just ahead of the knife velocity, wider sheets of veneer, and a more edge. This compression reduces splitting of the uniform cutting condition. Full rotary cutting wood ahead of the knife, reduces breaks into is approximately tangential to the annual rings the veneer from the knife side, and forces the and knots are exposed at their smallest cross knife bar assembly against the feed mechanism, section. In full rotary cutting, there is no im- thereby helping control veneer thickness. For pact at the start of cutting or tearofF at the end both the lathe and slicer, the pressure bar is, of cutting as may occur when slicing or cutting therefore, important in controlling the rough- with a stay-log. ness, depth of checks, and thickness of the veneer. The slicer has a fixed nosebar while the Advantages of Slicer lathe may have a fixed nosebar or a rotating A main advantage of the slicer is that it per- roller bar. mits sawing the log into flitches to present the most decorative grain pattern. As the veneer Advantages of Lathe sheets are kept in consecutive order, figured Logs to be cut into veneer on a lathe need to veneer can be readily matched. Flitches can be be crosscut to the desired bolt length, but they heated with less danger of end splits developing do not need to be processed through a sawmill than in comparable bolts being heated for ro- prior to cutting veneer. After roundup of the tary cutting. Sliced veneer is always cut from bolt, the lathe cuts a continuous strip of veneer. a flat surface, and most veneer is used on a flat

47 KNIFE AND FIXED BAR KNIFE AND ROLLER BAR M 144 168 Figure 19.—Knife and pressure-bar terminology. Symbol Preferred Term Alternate Term A Knife angle Knife pitch B Knife bevel angle Knife sharpness angle C Clearance angle D Lead Vertical opening * E Pressure bar bevel Pressure bar sharpness angle F Gap Horizontal opening * G Exit gap Restraint H Nosebar compression angle Bar angle I Knife surface next to wood work piece ** J Knife surface next to wood veneer ** K Length of knife bevel * Satisfactory for vertically operating lathe or slicer but is misleading for horizontally operating slicers. ** The term knife face is sometimes applied to J by knife manufacturers and to I by lathe operators. To reduce ambiguity, this terminology is suggested.

48 surface. By contrast, rotary veneer cut from a cut. Then as the veneer is cut, it separates into curved surface must be flattened for most uses. pieces the same width as the spacing of the The disadvantage of cutting from a curved sur- knives on the back-roll. face becomes more pronounced with thicker Since the scoring knives cut slightly deeper veneers cut from small-diameter bolts. than the veneer thickness, they generally leave Sliced veneer is cut with a draw motion a light score mark on the tight side of the next across the knife, while rotary veneer is cut with piece of veneer. The back-roll lathe is, there- no draw motion. Theoretically, the draw cut fore, better suited for cutting thick container should aid cutting. However, recent experi- veneer than thin decorative veneer. ments at the U.S. Forest Products Laboratory All lathes are generally equipped with spur indicate that the effect of the draw cut on knives so veneer can be cut to one or more smoothness, tightness, and veneer thickness is lengths while it is being peeled. relatively unimportant. Some General Comparisons of Veneer Veneer as long as 16 feet is produced on a slicer while most rotary-cut veneer is 10 feet or Cut on the Lathe and Slicer shorter. The flitch on a slicer is backed by the In general, the greatest yield is obtained by flitch table while support for a veneer bolt may rotary cutting. Half-round, flat-slicing, or back be provided by a backup roll. cutting provide intermediate yields; and the least yield is obtained by quarter- or rift-slicing. Advantages of Cutting with Stay-Log The smoothest and tightest veneer can be on Lathes produced by quarter- or rift-slicing, followed by rotary cutting ; the roughest and loosest veneer The stay-log makes it possible to produce is produced by flat slicing, half-round, or back- veneer on a lathe, similar in appearance to cutting. Differences in roughness are due to the sliced face veneer (fig. 11-C). The advantages effect of wood structure orientation (S9), of stay-log cutting on the lathe are very similar While slicing and rotary cutting involve some to the advantages of slicing. The flitches can be differences and inherent advantages, good-qual- selected for appearance of the grain and consec- ity veneer can generally be produced by either utive sheets can be matched for decorative method. The quality of the end product is de- faces. Sheets cut with the stay-log are generally termined more by the log quality, the heating wider than sheets cut on the slicer. For ex- of the bolts or flitches, and the setting of the ample, half-round veneer cut with a stay-log knife and pressure bar than by differences in would probably be slightly wider than flat-sliced the cutting method. veneer cut from the same log. Veneer cut with a stay-log is taken from a curved surface in Undesirable Movement of Wood and comparison with veneer that is sliced from a Machine Parts flat surface. Veneer cut with stay-log may be Knife and pressure bar settings are meaning- up to 10 feet in length. ful only if the wood is held securely in the lathe or slicer and if the machine parts have a mini- Back-Roll Lathe mum of play. A modification of the rotary lathe is the back-roll lathe (fig. 20). It cuts the veneer rib- Undesirable Movement of Wood on Lathe bon to preset widths and so replaces a clipping Bolts are held by chucks in a lathe. In gen- operation. This special type of lathe has ways eral, the larger the chucks the more securely that carry the knife-bar head-blocks extended the bolt is held. The chucks transmit the torque out on the log side of the lathe. On the extended needed to cut the veneer and also must resist ways, a frame is mounted to carry the back-roll. the tendency of the bolts to ride up on the knife. The entire mounting is fed toward the log by The spurs on the chucks should, therefore, be feed screws at the same rate at which the knife designed not only to transmit power to turn the is fed. Knives mounted radially in the back-roll bolt but also to keep it from shifting from the make an impression into the veneer bolt slightly spindle center. The best spur configuration is deeper than the thickness of the veneer being not well established. Some mills prefer half

49 SIZED VENEER

M 140 658 Figure 20.—Back-roll lathe. circles; others, star-shaped spurs and a ring high hydraulic end pressure is used during cut- around the circumference of the chuck. In prac- ting, the wood bolt may bend when it reaches a tice, the spurs sometimes become battered and small diameter. bent and may collect wood debris. For best per- Another modern solution to holding the bolts formance, they should be in their original shape more securely is the use of retractable chucks. and clean. The chucks and spindle ends should Larger chucks and spindles hold the bolt at the be tapered for a positive secure fit. start of peeling ; they are retracted during peel- The pressure used to set the chucks in the ing, allowing smaller inner chucks and spindles bolt ends depends on the wood species, heating, to hold and drive the bolt until the final core and chuck size. Generally, enough pressure is diameter is reached. A modification of this is used to indent the spurs at least three-fourths sequentially retractable chucks such as 5-inch their length into the bolt ends. Square-cut bolt (13 cm) inner chucks, with one 8-inch (20 cm) ends allow a more uniform grip than bolts that outer chuck on one end and one 12-inch (30 cm) are end trimmed on a bias. outer chuck at the other end. The bolt is first The wood in contact with the spurs receives driven with the 12-and 8-inch chucks. At a bolt fluctuating loads during cutting, which may diameter of about 14 inches (35 cm), the 12- cause the bolt to become loose in the chucks. inch chuck is withdrawn and the bolt is then On older lathes, the operator must watch for driven with one 8- and one 5-inch chuck. At a this and further indent the spurs if any loose- diameter of about 10 inches (25 cm), the 8- ness of the bolt is observed. Newer lathes have inch chuck is withdrawn. Cutting is continued hydraulic chucking. A relatively high pressure with the two 5-inch chucks driving the bolt to is used to set the chucks and then a lower the final core diameter. pressure is maintained hydraulically to insure To obtain maximum recovery, bolts are the spurs remain seated during cutting. If too turned to as small a diameter as practical. The

50 bolt is loaded as a beam by the knife and pres- The wear problem with feed screws is greatly sure bar. Its resistance to bending is directly reduced by a ball feed screw drive. Motion of related to the cube of the radius of the bolt. the carriage for the pressure bar and knife is At small bolt diameters, an unsupported bolt obtained by ball bearings turning a ball screw. bends in the middle away from the knife. The This movement by rolling friction means less bolt becomes barrel-shaped and the veneer rib- wear than for sliding friction with an acme bon wrinkles in the middle. To overcome this screw and nut. problem, backup rolls have been built to support Most production lathes develop some play the bolt during cutting. between the knife frame and the bar frame. Some early backup rolls operated with a The amount of movement depends on the loose- fixed pressure against the bolt. But this caused ness in the lathe and the amount of pressure problems. The cutting force fluctuates during exerted against the bar during cutting. To de- peeling, and a fixed pressure against the bolt tect and correct for this play, dial gages should surface sometimes increased rather than re- be mounted at each end of the lathe with the duced bowing of the bolt. gage on the knife frame and the sensing tip Improved backup rolls fix their position geo- against a bracket on the bar frame. These gages metrically to keep the bolt cylindrical. One should be zeroed after setting the gap or hori- method of doing this is a servo-system with a zontal opening. Any play will show on the gages follower at the end of the block that signals as a reading other than zero and the original adjustments of pressure on the backup roll. gap or horizontal opening restored by adjusting Another method (22) is to have this backup the nosebar until the gages read zero. roll positioned mechanically by the feed mecha- Walser (67) describes a method to preload nism so the bolt remains a cylinder. the pressure bar assembly to improve accuracy When properly made and operated, backup when setting the veneer lathe. rolls permit cutting bolts 8 feet long (2.44 m) Play can also affect the lead or vertical open- to a final core diameter of about 4 inches ing. This is less common than play in the gap (10 cm). or horizontal opening. Again, dial gages can be mounted to detect and guide correction of the Undesirable Movement or Play in Lathe play. Machine Parts Spindle Overhang All movable parts must have some clearance, Other things being equal, the greater the and wear increases this clearance. Many lathes overhang of the spindles the more spring in have built-in methods of taking up slack as the cutting system. This is most noticeable wear progresses. However, it is not uncommon when short bolts are cut on a long lathe. If both to find that production lathes have developed short and long bolts are to be cut on the same excessive wear and looseness or play in the lathe, the lathe should be equipped with spindle mechanism. Some specific areas to check are steady rests. spindle sleeves and bearings, feed screws, head- block or knife-angle trunnions, nosebar eccen- Heat Distortion of Lathe tric, and blocks under screws used to change Bolts that have been heat-conditioned prior the lead (vertical adjustment) of the pressure to cutting may cause the knife and pressure bar. The greatest wear is likely to be in the bar to distort. It is generally agreed that heat- spindle sleeves and bearing, with the next ing causes the knife to rise in the middle, de- largest amount in the feed screws and movable creasing the lead. Heat may cause the pressure parts of the nosebar assembly. Some modern bar to drop or move in a horizontal plane, de- lathes minimize these problems by using pre- pending on the lathe. On some lathes, one loaded roller bearings for the spindles and an method of correcting for these changes is to air cylinder to keep the knife bar always adjust the pull screws on the A-frame built against one side of the feed screw. In addition, over the pressure bars for this purpose. A bet- some lathes have replacable wear surfaces for ter solution is to heat the knife and pressure the ways. bar to the expected operating condition prior to

51 the final fitting (setting) of the knife and bar. Undesirable Movement or Play in Some lathes have had heating elements built Slicer Parts in them to prevent heat distortion. Play can develop in all moving parts such Another good practice is to store sharpened as feed screws, offset mechanism, flitch table knives in a warm area so they are at the same ways, and knife-bar carriage ways. Most mod- temperature they attain during cutting. Feihl ern slicers have means of taking up slack in and Godin {H) suggest heat distortion can also these parts. A regular maintenance schedule be controlled by continuous cooling of the knife should be followed. bed and the pressure bar bed. However, they and others indicate heating the knife and bar Feed by Pawl and Ratchet works better than cooling, particularly for long Some slicers advance the knife by a pawl and lathes. ratchet for each stroke. This is highly accurate providing the same number of teeth are ad- vanced each stroke, there is little play in the Undesirable Movement of Wood on Slicer feed mechanism, and there is no overtravel of The wood flitch is generally held against the the carriage. The number of teeth advanced bed on a vertical or horizontal slicer with dogs. each stroke should be checked several times be- In some vertical and all horizontal slicers, grav- fore and during actual cutting. The brake on ity helps hold the back of the flitch against the the shaft which advanced the knife each stroke flitch bed. However, in the most common ver- should be adjusted so there is no overtravel. tically operating face veneer slicers, the flitch Feed to a Stop Plate is cantilevered from the bed and dogging is very important. Some slicers feed by moving the previously Heated flitches may be bowed or twisted. cut surface against a stop plate. The surface Very often this bow or twist can be removed of the flitch and of the stop plate must be free by forcing the flitch flat against the flitch table of splinters or other debris and the flitch must be advanced flush to the stop to produce veneer and dogging it securely. Here oversized dogs are useful at the start of the cutting. A recent of uniform thickness. development has been retractable dogs, which Offset on Vertical Face are extended for maximum holding power at Veneer Slicers the start of slicing and then automatically re- The offset mechanism on modern slicers is tracted when the slicing cut approaches the hydraulically operated and does not generally dogs. require attention once the cam is set to retract Older slicers had the dogs set by screws. the knife at the bottom of the stroke. The After intermittent cutting, the flitch would amount of offset is adjustable and should be often become loose, so the slicer would have to large enough to insure clearance of the flitch be stopped and the dogs reset in the wood. on the upstroke. Excess offset should not be Modern slicers have hydraulic dogs which used as it may induce slight vibration to the maintain good contact with the flitch through- knife. The knife and bar carriage pivot on half out cutting. The hydraulic cylinders actuating bearings for the offset. Since the half bearings the dogs have check valves to prevent the flitch are not held at the top, if the flitch fails to from shifting during slicing. clear on the upstroke, the knife bar carriage A recent practice is to glue valuable flitches may be lifted from the half bearings. Similarly, such as walnut to an inexpensive backboard high nosebar pressure cannot be used without and then slice to the glueline. Special glues and danger of unwanted movement of the knife gluing techniques are used to bond the hot wet carriage on the half bearings. flitches to the backboards. Another innovation As with the lathe, it is desirable to have dial is to hold the flitch against the table with a gages mounted at each end of the slicer with pattern of vacuum cups. The flitch back should the gage on the knife frame and the sensing tip be wide, smooth, and flat or the flitch may against a bracket on the bar frame. The gages break loose from the table during cutting. are particularly useful for returning to the

52 previous setting after the bar has been re- the slackness in the lathe will be taken out by tracted to hone the knife. the time the veneer is wide enough to use. This Heat Distortion of Slicer veneer will be more uniform in thickness than veneer cut just after the pressure bar has been Since face veneer slicers are generally longer closed. than lathes, heat distortion of the knife and Some slicer operators set to cut tight veneer bar may be more of a problem. As on the lathe, and run into a gradual buildup of the flitch the heated knife rises in the middle and the face with respect to the knife due to cutting pressure bar drops. The pull screws on the veneer thinner than the feed. Eventually, the A-frame on the casting holding the bar can knife carriage will vibrate due to excessive compensate for movement due to heat. A better pressure against the knife and pressure bar. solution, and one that is built into modern The operator will then throw off the feed for slicers, is a means of heating the knife and bar one stroke, cutting a thick shim and continue prior to fitting them, and then keeping these to cut. This is poor practice as consecutive parts continually warm. This not only greatly sheets cut after each shim are gradually chang- reduces any changes in the knife-bar setting ing in thickness. Better practice is to change due to cutting hot flitches, but also reduces con- the pressure bar setting (larger lead or gap) densate and the iron-tannate stain that results so that a constant full thickness veneer will be when iron or steel particles come in contact cut. with wet wood. Eflfect of Speed of Cutting on Dynamic Equilibrium on Lathe and Slicer Veneer Quality Many have observed that the first sheets When Knospe (SS) reviewed some of the from a flitch on the slicer and the first few veneer cutting literature in 1964, he concluded revolutions of veneer from a bolt on the lathe that cutting speed has a minimal influence on are thinner than the nominal knife feed. Hoad- the quality of veneer. Recent unpublished work ley (29) studied this phenomenon with a knife by A. 0. Feihl indicates that for practical pur- and pressure bar mounted on a pendulum dyna- poses this is true within the speeds of about mometer. He attributed the thin first cuts pri- 100 to 500 feet (30 to 150 m) per minute. marily to compression of the wood beyond the However, at least two studies (6,JfS) have thickness of cut, followed by springback after shown that the strength of the veneer in ten- the cut. With the same advance, both the com- sion perpendicular to the grain decreases with pression and springback became progressively an increase in cutting speed. Lower strength in larger until a full thickness chip was produced. tension perpendicular to the grain is generally Hoadley called this dynamic equilibrium. caused by deeper checks into the veneer. In Later studies on both an experimental and addition, high cutting speed with wood species commercial lathe at the Forest Products Labor- having a very high m.oisture content may in- atory Hi) indicated that the thin cuts were crease the incidence of mashed grain and shell- due mainly to takeup of slackness in the lathe. ing. Veneer cut from a small, more rigid experi- In summary then, the cutting speed does not mental lathe reached full thickness quicker seem to be a critical controlling factor for most than veneer cut on a 4-foot-long commercial veneer production. However, if optimum veneer lathe. When the pressure bar was against the tightness and smoothness are important, it may wood, it tended to force the bolt and knife in pay to use a moderately slow cutting speed. opposite directions. When the bar was re- When slicing %-inch and thicker veneer, there tracted and the knife alone engaged the bolt, may be a slight vibration of the slicer due to the knife and bolt were drawn together. As a the impact at the start of the cut. Inclining the result, opening the bar (for example, to clear a length of the flitch 3° to 5° from the long splinter) during cutting results in large changes direction of the knife lessens this impact as of veneer thickness on a lathe that has slack- the cutting starts at one corner of the flitch. A ness. In contrast, if the pressure bar is kept slower speed also reduces the impact at the closed from the start of cutting, then much of start of each cut.

53 KNIFE AND PRESSURE BAR ON LATHE AND SLICER

Type of Knife Selecting the Knife The knife represents the largest maintenance Most veneer knives are supplied the full cost in cutting veneer and consequently it is length of the lathe or slicer. However, two- and worthwhile to use good purchasing specifica- three-piece knives are sometimes used with a tions and take care in grinding and setting the special clamping arrangement so they can be knives in the lathe or slicer. ground and set as a unit. If one section is What should be specified when ordering a damaged, it can be replaced without replacing knife for the lathe or slicer? The length of the the entire knife. knife and presence or absence of slots and their The hardness of the knife should be specified spacing will be determined by the equipment and can readily be tested. A soft knife can be on which the knife will be used. Other factors easily honed and is tough but also wears such as depth, thickness, hardness, insert or rapidly. A hard knife is diflftcult to hone, is solid, and the grind can be specified. In addi- more likely to chip if it hits something hard, tion, the percent carbon and other components but holds a sharp edge much better. Most rotary of the steel could be specified. However, the veneer plants prefer a knife with a Rockwell exact components of the knife steel are gener- hardness on the C scale of 56 to 58. Knives for ally not published by knife manufacturers. As face veneer slicers are often 58 to 60 on the a result, most veneer plant managers deal with Rockwell C scale. To keep as sharp an edge as a reputable knife manufacturer and specify possible when cutting low-density woods like only the size, shape, hardness, and whether basswood, a knife with a Rockwell hardness they want an insert or solid blade. An ideal of 60 to 62 may even be used. knife should have maximum stiflfness, tough- Bevel angle, wedge angle, and sharpness ness, corrosion resistance, and wear resistance. angle all refer to the angle that results from The most common knife thickness for lathes the intersection of the two surfaces which form is % inch (16 mm), and for face veneer slicers, the knife edge. This and other terminology % inch (19 mm). Thinner knives such as V2 inch used with the knife and pressure bar are shown (13 mm) are sometimes used on the lathe; they in figure 19. The knife bevel angle may vary are less expensive but also less stifli. The Euro- from about 18° to 23°. The smaller the angle, pean horizontal slicers may use a knife ^%2 inch the less the veneer is bent as it is cut and hence (15 mm) in thickness, supported with a blade the tighter the veneer. In contrast, the larger holder. In general, the veneer knife should be the bevel angle the stiffer the blade and the thicker when cutting thick veneer. When cut- better the edge can withstand impact. More ting thin veneer, thinner knives can be used if care must be taken when grinding the smaller they are properly supported. bevel angles as the knife tip is more likely to The choice of an inlaid knife or one hardened heat than when grinding a knife to a large throughout may depend on the end product. bevel angle. Hardwood face veneer is generally cut with an inlaid knife. The mild steel used for backing is An 18° bevel angle may be used to slice prop- stable and easy to grind. It can be readily erly heated flitches of eastern redcedar while a drilled so that the knife can be held firmly 23° bevel angle is often used to rotary cut when back grinding. The highly refined hard- bolts of unheated softwoods. Many veneer ened tool steel insert is generally of highest knives are ground to a bevel angle of 20°or 21°. quality for cutting wood. Some lathe and slicer operators prefer to Knives that are hardened throughout report- measure the length of the knife bevel rather edly may stand up better when cutting hard than the knife bevel angle (fig. 19). Some rela- knots. They are sometimes, but not always, tions of knife thickness, knife bevel angle, and used in plants producing construction plywood. knife bevel length follow :

54 Knife Thickness Knife Bevel Knife Bevel it possible to cut abrasive wood longer between Angle Length honings. A microbevel about 0.015 inch wide Inch Degrees Inch is often applied at the edge of the knife to 1/2 (0.500) 18 1.618 make the included angle about 30° (10). If a 19 1.536 tough knife could be made from tungsten car- 20 1.462 21 1.395 bide ground to a 20° included angle, this should 22 1.335 be a good material for cutting wood containing 23 1.280 silica or calcium carbonate crystals. 5/8 (0.625) 18 2.023 19 1.920 The third method of knife wear is corrosion 20 1.827 as described by Kivimaa (SI ) and by McKen- 21 1.744 22 1.668 zie and McCombe (^7). Acetic acid and poly- 23 1.600 phenols in some woods react with the steel 3/4 (0.750) 18 2.427 knife and corrode it. This reaction makes the 19 2.304 20 2.193 common blue iron stain that is so objection- 21 2.093 able on face veneer as well as causing wear of 22 2.002 the knife. Kivimaa (SI) found that knife wear 23 1.919 was greatly retarded by putting a positive The ground surface is generally slightly con- potential on the wood work piece and a nega- cave to make the knife easier to hone. For the tive potential of 1,500 volts on a planer knife. lathe, the recommended hollow grind is 0.002 to Later at Madison we put a positive charge 0.004 inch (0.05 to 0.10 mm) while slicer of 300 volts on a rigid pressure bar on a lathe knives generally have a hollow of 0.001 to 4 feet (1.2 m) long and a negative charge on 0.002 inch (0.025 to 0.05 mm). The flatter the knife. The charge greatly retarded blue grind for a slicer knife means less chance for stain from the knife as compared to the stain the flitch to rub against the heel of the knife that developed on oak veneer when the lathe and stain the wood. More hollow can be used on was stopped momentarily without a charge to a lathe knife as the bolt surface curves away the pressure bar. However, a shallow brown from the ground surface of the knife. However, stain occurred on the veneer next to the knife. the hollow should not exceed 0.004 inch (0.10 In addition, blue stain from the tool steel pres- mm) as this weakens the knife edge. While the sure bar became worse. When a stainless steel details of the knife bevel can be changed by pressure bar was used, the blue stain was grinding at the veneer producing plant, the nearly stopped next to the bar but the shallow knife should be ordered as it will be used to brown stain again occurred on the wood next eliminate an extra grinding. to the tool steel knife. Ralph Scott, a research Knife Wear chemist at the U.S. Forest Products Labora- Knife wear apparently takes place by three tory, checked the wood next to the knife (nega- methods: Impact, abrasion, and corrosion. Im- tive terminal) and found it to be a strong base pact and abrasion are mechanical phenomena (pH 10 to 12). Apparently hydroxyl ions were while corrosion is chemical in nature. released at the negative terminal and formed Mechanical impact is most obvious when a a base that turned the wood brown. hard object, such as a small piece of gravel, Another difficulty with running 300 volts chips the knife edge. Damage due to mechani- direct current from the pressure bar to the cal impact may also occur when the knife hits knife was that sap forced from the bolt ends hard, unheated knots. Such knots may turn the made a short and the arc caused a big crater extreme edge of the knife. Woods containing in the knife at this point. A third problem was 1 percent or more of silica or calcium carbon- that the stain was spotty over the 4-foot (1.2 m) ate are abrasive and rapidly wear a rough edge length of veneer, indicating the electric cur- on a veneer knife. Use of a tough tool steel rent took the path of least resistance and so rather than a brittle steel may help reduce the was not acting uniformly to reduce stain and damage due to mechanical impact. Use of a knife wear. microbevel (10) or back bevel reduces the McKenzie and McCombe (Í7) successfully chance of damage due to impact and may make rotary-cut bolts 4% inches (12 cm) long with

55 the knife held at a negative potential of 60 which the grinding wheel traverses, the knife volts with respect to the nosebar. They report bed should be adjusted until it is parallel to the that knife wear was reduced 60 percent. ways. In spite of the difficulties in applying a posi- To maintain even wear of the ways, the tive electrical potential to the bolt or flitch and grinding wheel should traverse the entire a negative potential to possibly both the knife length of the grinder even when grinding short and pressure bar, the method does look tech- knives. nically interesting. An alternative would be The surface of the knife that goes against development of stainless knives than can hold the grinder bed must be checked for bumps or an edge sharp enough for good veneer cutting. other rough spots that will prevent the knife from lying perfectly flat. If necessary, the back Grinding Veneer Knives of the knife should also be ground to restore a The purpose of grinding is to restore a plane surface. (See "Back Grinding.") straight, sharp, tough edge. If these three re- Heat can cause metal to expand and deform. quirements are kept in mind, they may help The grinder and knife should therefore be kept guide good grinding practice. at as uniform a temperature as possible during In order to grind a straight edge, it is neces- grinding. An example of poor practice was a sary to start with a rigid level grinder. The grinder set near a radiator. During summer most satisfactory veneer knife grinders have a the knife bed was straight. However, in winter fixed bed for mounting the knife and a travel- with the radiator on, the grinder bed was ing grinding wheel. heated on one side and warped enough to result The abrasive may be a solid cup wheel or a in unsatisfactory grinding. Similarly, the water segmented wheel. Some operators prefer the used to cool the grinding wheel and knife should segmented wheel because it requires less dress- be at room temperature and be recirculated. A ing and replacement segments are less expen- stream of water with synthetic coolant should sive than a new cup wheel. be directed against the grinding stone '¥1 inch A magnetic chuck makes it faster to set the ahead of where the stone contacts the knife knife for grinding. A V-belt drive in place of edge during grinding. gears reportedly reduces chatter marks on the Godin (2i) considers overheating of the knife. knife tip the most serious problem in grinding The knife bed as well as the ways on which and lists four main causes: (1) Too heavy a the grinder moves must be rigid, straight, and cut; (2) inadequate cooling; (3) clogged grind- parallel to one another. The ways are generally ing wheel; and (4) too hard a grade of grind- hand scraped for accuracy when the grinder is ing wheel. Heating is less likely to occur if the made. The ways should have wipers to keep knife edge is pointed up and engages the grind- them clean in use. The accuracy of the ways ing wheel first during grinding. A feed of can be measured in the veneer plant by travers- 0.0003 to 0.0005 inch (0.0008 to 0.012 mm) is ing them with a dolly holding a gage. A special suggested for each complete traverse of the telescope with a measuring crosshair is leveled wheel. At the FPL we like to dress the wheel like a transit and then sighted on the gage on and use a very fine feed for the last one or the dolly. The dolly is moved along the ways two traverses of the sharpening. This helps and any deviation from a straight line can be give a fine surface. Some manufacturers polish recorded. If the ways are not straight, they the knife by multiple passes without feeding. must be straightened at the factory. After the The smooth edge reportedly aids good veneer ways have been determined to be straight, they cutting. Care must be used with this technique are used as a reference to determine if the knife or the grinding wheel may rub, heat, and bed is straight and parallel to the ways. This weaken the knife tip. can be readily done in the veneer plant by Another cause of an irregular edge is dubbing indexing with a surface gage, such as a dial at the two ends of the knife. The most likely indicator, from the grinding wheel carrier causes are looseness in the grinding wheel which moves on the ways. spindle bearings, excessive end play, and slack If the knifebed is not parallel to the ways on in the feeding mechanism. However, even a

56 grinder in good mechanical condition may knife develops a heavy wire edge, the grinding slightly round the ends of the knife. This may wheel can be stopped and the wire edge removed not be a problem as the end inch or two of the while the knife is still clamped in the grinder. A knife generally does not engage the wood when few more passes of the wheel will create a new cutting veneer on a commercial lathe or slicer. fine wire edge that can be easily removed by If it is important to have the knife straight to honing. After the wire edge is removed, the the extreme ends, then dummy knife sections edge is finished by lightly honing with a fine- 4 to 6 inches (10 to 15 cm) can be attached textured stone that has been stored in kerosene. to the knife bed at the two ends and in line More detailed suggestions for grinding and with the knife being ground. Sections of a dis- honing veneer knives are contained in Cana- carded knife can be used for this. The dummy dian Forestry Service Publication No. 1236 sections absorb the heavier cut at the start of {2Í). each traverse of the wheel and the main knife is not dubbed at the ends. Secondary Knife Bevels Back Grinding When a sharp knife ground to a bevel angle of about 21° is first put in the lathe or slicer, After a knife is used, it may wear unevenly it is easily nicked by a knot or other hard sub- on the side where the veneer passes through stance. These nicks are removed by honing the the throat between the pressure bar and the knife in place on the lathe or slicer. After sev- knife. It may also be bent by excessive local eral bolts or flitches are cut, the knife edge pressure as from a knot or chip buildup. This wears slightly and this, plus the honing, makes can be detected by placing a straightedge at the extreme edge more resistant to damage. a right angle to the cutting edge. If this surface This condition is sometimes called a work-sharp is not flat, then grinding the side of the knife knife. When examined under a microscope, the that goes next to the bolt or flitch will not edge is seen to be slightly rounded so it is result in a straight edge. The solution is to probably closer to 30° to 35° than to 21° at the grind a flat surface on the veneer side of the extreme tip. Such a knife will remain sharp and knife. The grinder bed is tilted ^/2° to 3° toward do a good job of cutting for several hours if no the knife and the knife is ground to produce a very hard material is hit. bevel % to 1-% inches long. A magnetic chuck on the grinder facilitates this grinding. Other- For other steel knives used to cut wood, such as planer knives, the smaller the bevel or sharp- wise, the knife body must be drilled and tapped not more than 12 inches apart so the knife can ness angle, the faster the knife wears. The rate be mounted securely for back grinding. of wear goes up much faster if the bevel angle Some modern grinders are equipped with or sharpness angle is less than 30° to 35°. This wear phenomenon is apparently the same for two grinding wheels so the face and back of the knife can be ground at the same time. veneer knives. Realizing this, the veneer indus- try has long had a practice of putting a back Haning Knife bevel on the knife. This strengthens the knife The knife should be ground only enough to edge and is commonly used with knives installed obtain a thin wire edge the length of the knife. on core lathes for peeling unheated softwoods. The wire edge is removed by careful honing Kivimaa and Kovanen {32), Feihl {10), and with a stone on one side of the knife, then the others have studied the use of a precision micro- other. The stone should be medium grain and bevel put on either side of the knife. They medium to soft in hardness. The stone should report that a second bevel can be honed on be saturated with kerosene. Some operators use either or both sides of the knife, and that the one stone and others use two stones, one on final included angle of 30° or 35° with a micro- each side of the knife simultaneously. In either bevel 0.010 to 0.020 inch in width greatly im- case, each pass of the stone cuts at the base of proves the strength of the knife edge. At least the wire edge and bends it away from the one commercial grinder has a separate grind- stone. After several passes, most of the wire ing wheel that can grind a microbevel at the edge will fall off. Honing is continued until all same time the main bevel is being ground. of the wire edge is removed. If a badly nicked Some slicer operators use a two-bevel knife.

57 The main bevel is 19° and the second bevel is the template indicates level. The same adjust- 21°. Grinding of the second bevel is continued ment is then made at the other end of the until the length of the second bevel is about knife. If the span is short and the knife deep V2 inch. When cutting, this is the only part of and stiflf, the knife height should be the same the knife that rubs against the flitch, and so across the lathe. However, with longer knives, the two-bevel knife reduces stain. Some opera- particularly those that have been ground so tors like the two-bevel knife and others do not. they are not so deep, the knife may sag in the middle. One way of checking this is to level a Setting Knife transit with a telescope about 20 feet (6 m) from the lathe and swing it from one end of Information on setting the knife and bar in the knife to the other. The knife edge should be a lathe assumes that the knife frame and bar in line with the crosshairs along its length. If frame of the machine are in proper alinement the knife sags in the middle, it should be raised with the center of rotation of the spindles. with the leveling screws near the center of the Similarly, it is assumed that the knife and bar knife. Once the knife edge is true, some opera- ways on the slicer are level and perpendicular tors make scribe marks on the lathe so they to the flitch ways. It is further assumed that can reposition knives with precision. Another there is a minimum of play in the moving parts method is to measure the extension of the knife of the lathe or slicer and that the machine parts are at the same temperature they attain from the top of the knife bed. To speed up knife changes, some lathes have in use. If these conditions are not met, the care- knife holders. After grinding, the knife is pre- ful setting of the knife and bar on the static set to the desired height in the holder, and the machine may be changed so much in the dy- holder quickly bolted in place in the lathe. Some namic cutting condition that poor quality veneer plants in effect preset the knife by pouring will be produced. Feihl and Godin (15) de- babbit metal at the bottom edge of the knife scribe methods of checking the basic alinement after each grind. The depth of the knife is thus of lathes. kept constant and the knife can then be placed Setting the Knife in the Lathe and Slicer on the height-adjusting screws without chang- A correctly ground flat knife with a straight ing them. cutting edge is the first requirement. If a knife Sag in the knife can also be checked with a holder is used, it must also be clean and flat. A tautly stretched fine wire. clean, flat bed on the lathe or slicer is the If there is wear in the spindle bearings, the second requirement. (If these conditions are bolt will ride up during cutting, taking up the not met, it is difficult or impossible to correctly play. To compensate for this, the knife edge is set the knife.) The knife or knife and knife sometimes set above the spindle centers the holder is then set on the two end adjusting same amount as the play in the spindles. This screws. The clamping screws are tightened by results in the knife edge being at the spindle hand so that the knife is flat against the bed centers during cutting. but free to move. To this point, the procedure After the knife is set to the spindle centers, is the same for the lathe and the slicer. the knife angle is adjusted. In general, the side of the knife that contacts the bolt is ap- Setting the Lathe Knife proximately vertical (tangent to the surface of After the knife is resting on the two end the bolt). Such a knife is said to have an angle adjusting screws on the lathe, the knife edge is of 90°. If the knife leads into the bolt 2°, the raised until it is level with the center of the knife angle is 92° and the clearance angle 2°. spindles. This can be facilitated by using a A lathe knife can also be set with a negative template consisting of an accurately machined clearance. A knife angle of 89° means the knife wood block cut out at one end to one-half has 1° negative clearance. the diameter of the spindle. The cutout end Most lathes are built so the knife angle can rests on the spindle and the other end on be made to change automatically with the bolt the knife edge. The height of the knife is then diameter. The objective is to keep the width adjusted until a spirit level on the back of of the knife surface that rubs against the bolt

58 about the same when cutting a bolt of a large To prevent these problems, some lathe opera- diameter as at a small diameter. For example, tors increase the angle of the knife until a when cutting at a bolt diameter of 3 feet (91 corrugated veneer surface results. They then cm), the knife angle may be 91° ; at a diameter reduce the knife angle gradually until the cor- of 6 inches (15 cm) the angle may be 89° 30'. rugations disappear and use this knife angle The means of changing the knife pitch varies for cutting. with different lathes. Feihl and Godin (15) For best results, we recommend determining describe several methods that can be used to and recording the knife angles that are satis- properly set the pitch ways. The lathe manu- factory and using an instrument for measuring facturers should be consulted for recommended this angle when the knife is set. procedure for use with their lathes. Instruments for measuring the knife angle In general, lathe operators use less lead into are described by Fleischer (19), Feihl and the bolt (lower knife angles) when cutting low- Godin (15), Fondronnier and Guillerm (21), density woods than when cutting thick veneer. and Dokken and Godin (9). While all are suit- For example, Fleischer (17) suggests a knife able, the French design (21) (fig. 21) and the setting of 90° 30' when cutting Viö-inch (0.8 Canadian design (9) are easily read. mm) yellow-poplar (low-density wood) and If the knives are all ground the same, they 90° 45' when cutting Mw-inch (0.8 mm) yellow can be interchanged on a lathe or slicer with- birch (high-density wood). Fleischer shows a out changing the knife angle or clearance angle. pronounced eifect of veneer thickness on the However, if the knives are ground so the bevel best knife setting. For Vmo-inch (0.25 mm) or sharpness angle is as little at 1-2° different, birch, he recommends a knife setting of 92°, the cutting can be altered significantly. Conse- for y32-inch (0.8 mm) 90° 45', for Mn-inch (1.6 quently, we recommend the knife angle be mm) 90° 15', and for Vs-inch (3.2 mm) veneer 90°. These settings are for log diameter from 20 to 12 inches (50 to 30 cm). When the correct knife angle is being used, the knife side next to the bolt will show Vic to VH inch (1.6 to 3.2 mm) of bright rub below the knife edge. If the correct knife angle is not used, the veneer may show this. Too high an angle causes the knife or bolt to chatter and results in a corrugation on the veneer and the bolt surfaces. The waves are closely spaced with three or more waves per inch of veneer width. Too low a knife angle results in too much bearing on the knife, forcing it out of the ideal spiral cutting line. When the force on the knife builds up, it may then plunge into the bolt, resulting in thick and thin veneer with waves a foot or more apart. Some lathe operators use low knife angles, as the heavy bearing of the knife against the bolt tends to smooth the surface of the veneer. Lathe and knife manufacturers do not like this practice because the pressures on the face of the knife may become so great that the knife will be bent and the knife failure blamed on M 130 i)3il the knife manufacturer. Low knife angles also Figure 21.—Instrument of French design for measur- ing the knife angle. It is held by magnets to the face require more power for turning the bolt and of the knife, the bubble is centered, and the knife angle cause more stain and wear to the lathe. is read on the vernier.

59 checked with an instrument after each knife into the veneer. It compresses the wood just change. ahead of the knife and so allows the knife to Setting the SHcer Knife cut rather than split the veneer from the bolt Setting the knife in the sheer is similar to or flitch. This helps control rough surfaces and setting the knife in a lathe except that the checks into the veneer. By keeping a force be- position of the knife edge in a sheer is set by tween the knife carriage and the flitch or bolt, the extension of the knife from the bed. The the pressure bar takes up slack in the machin- sheer knife edge should extend above the knife ery always in the same direction and so aids bed just enough so the ground face of the knife control of the veneer thickness. clears the bolts that hold it against the knife There are two common types of pressure bars bed. In other words, the knife should extend as —the fixed pressure bar and the roller pres- little as possible and still make certain the sure bar. flitch will clear. On vertical face veneer slicers, this distance is about 2 inches. Fixed Pressure Bar Like the lathe knife, the slicer knife should rest Two factors to consider when selecting a on the two end adjusting screws. The knife is fixed pressure bar are its stability and wear then brought against the bed and any sag in resistance. The most common metals are tool the middle is removed with the height-adjusting steel, steinte, and stainless steel. The tool steel screws near the middle of the slicer. Since bar is relatively stable, machines easily, and is slicer knives are often longer than lathe knives, relatively inexpensive. A stellite bar is more this adjustment is more critical on the slicer. expensive, harder to grind, and less stable. A taut ñne wire can be used as a guide to deter- However, the stellite bar will wear many times mine sag in the knife or, if the pressure bar bed longer than the tool steel. Stainless steel is is known to be straight, it can be used as a easier to grind than stellite and, like stellite, guide. A pressure bar that has been ground does not stain the veneer. uniform in thickness is brought up against the The fixed bar is generally ground to a bevel pressure bar bed. The bottom of the pressure angle of about 74° to 78°. As the wood bolt or bar can then be used as a reference to deter- flitch approaches the fixed bar in the lathe or mine if there is a sag in the slicer knife. slicer, the wood is compressed along a plane Once the knife edge is determined to be 12° to 16° from the motion of the wood. When straight, the knife is bolted firmly in place and cutting ^As inch (0.9 mm) or thinner veneer all of the adjusting screws are brought in con- from dense hardwoods, the bar should be tact with the bottom of the knife. ground to a sharp edge. The edge of the bar is The knife angle of the slicer is relatively generally slightly eased or rounded when cut- easy to set compared to the lathe knife. Since ting thicker veneer from low-density woods or all cutting is from a flat surface, the knife woods subject to rupture on the tight side of angle does not change with flitch diameter. the veneer from rubbing against the bar. Vari- Further, the knife must lead into the flitch so ous researchers recommend an edge radius of the heel of the knife does not rub hard against about 0.015 inch (0.3 mm). But Fleischer (17) the flitch. Experimentally, we have found that reports rounding the bar to Vs-inch (3.2 mm) a sheer knife angle from 90° 20' to 90° 30' radius did not improve the smoothness of west- (about V2° clearance angle) can be used to slice ern hemlock veneer and may be disadvan- wood from Vioo to % inch (0.25 to 6.3 mm) in tageous. thickness from both low-density and high- density woods. Roller Pressure Bar Like the lathe knife, the angle of the slicer The roller bar is the second major type of knife should be checked with an instrument pressure bar. In U.S. practice, the bar is com- each time a knife is replaced. monly of bronze, generally % inch (15.9 mm) in diameter if it is a single bar and %> inch Pressure Bar (12.7 mm) in diameter if it is a double roller The pressure bar is important for control- bar. The single roller bar is driven directly ling thickness, smoothness, and depth of checks while the double roller bar is driven with a

60 backup roll. Two advantages of the double position of the bar with respect to the knife is roller type stand out: (1) The drive roller can fixed if any two of the three openings are fixed. be larger so there is less breakage of the For example, if the lead and gap are set, this rollers, and (2) the knife and pressure bar can also automatically sets the exit gap. Which two advance very close to the chucks, permitting are chosen for setting the knife and bar should peeling to smaller diameter cores than with a depend on the ease with which the openings single roller bar. The drive chain for a single can be measured and on how the knife and bar roller bar may protrude up to 1 inch beyond can be adjusted on a specific lathe or slicer. the surface of the roller bar. Roller bars are Examples of how these three openings are generally lubricated with 1 percent vegetable interrelated for different veneer thicknesses oil mixed in water and introduced through and different settings are given in tables 8 holes in the cap that holds the bar. through 11. Comparison of Fixed Bar and Roller Bar Setting Fixed Pressure Bar on Lathe The fixed bar is the simplest and most com- (by Lead and Gap) monly used pressure bar. It is used exclusively When the knife edge and the pressure bar on slicers and is by far the most common bar edge are ground straight, it is much easier to used to cut hardwoods on a lathe. The roller set the bar. These two edges must be straight bar is more common in the United States for and as perfectly alined as posible for precision cutting West Coast softwoods and has occa- veneer cutting. All the precautions suggested sionally been used to cut eastern softwoods and under knife grinding should also be used when hardwoods. The fixed bar can be used to cut grinding a new edge on a fixed pressure bar. veneer of any thickness. The %-inch (15.9 mm) The bed for the bar and the nosebar cap diameter roller bar cannot be set to cut veneer should be clean and straight. The bar is in- much thinner than Vio inch (1.6 mm). Most serted between the bed and the cap and the veneer peeled with the aid of a roller bar is nosebar locking screw tightened just enough used in construction plywood and is yi2 inch to hold the bar against the bed but loose enough (2.1 mm) or thicker. In general, it is easier to so the bar can be moved without bending it. set a fixed bar precisely than a roller bar. The bar should extend from the supporting A major advantage of the driven roller bar casting only a minimum amount so it is a rigid is that it requires less torque to turn a bolt; as practical. this in turn means less spinout of the bolts at After the knife is set, the bar is moved the chucks and less breakage at shake and toward the knife with adjusting screws at the splits in these bolts. Another advantage of the two ends of the bar until the bar is about %2 roller bar is that it pushes through small inch (0.8 mm) behind the knife edge. splinters that otherwise may jam between a Setting Lead fixed bar and the bolt and degrade the veneer. The nosebar bed on most lathes has adjust- ing screws at the two ends that allow the entire Setting Pressure Bar bed to be raised or lowered, increasing or de- The information on setting the pressure bar, creasing the lead of the nosebar edge with like the information on setting the knife, respect to the knife edge. The amount of lead assumes the lathe or slicer is in good mechani- (vertical opening) is adjusted primarily for cal condition with a minimum of looseness in the thickness of veneer being cut. Some lathe moving parts. The knife, pressure bar, and operators set the lead one-third of the thick- surrounding metal parts on the lathe or slicer ness of veneer being cut. Fleischer (17) sug- should be at the approximate temperature they gests there is a straight-line relationship with will attain during cutting. a lead of 0.0005 inch (0.12 mm) when cutting Cross sections of the knife with a conven- Moo inch (0.25 mm) and a lead of 0.030 inch tional fixed bar and a roller bar are shown in (0.8 mm) when cutting Vs-inch (3.2 mm) figure 19. Three openings between the knife veneer. Some settings using a variable lead and the bar are indicated—the lead, gap, and that depend on veneer thickness are shown in exit gap. With any knife-bar combination, the table 9. Certain lathes made in Germany do not

61 Table 8.—Lathe settings with a fixed bar and a constant lead

Feed (veneer thickness) Lead Gap Exit gap In. Mm In. Mm In. Mm In. Mm 0.010 0.25 0.030 0.76 0.009 0.23 0.019 0.48 .032 .81 .030 .76 .029 .74 .038 .97 .042 1.07 .030 .76 .038 .97 .046 1.17 .0625 1.59 .030 .76 .056 1.42 .063 1.60 .100 2.54 .030 .76 .090 2.29 .095 2.41 .125 3.17 .030 .76 .112 2.84 .115 2.92 .1875 4.76 .030 .76 .169 4.29 .168 4.27 .250 6.35 .030 .76 .225 5.71 .221 5.61 I Fixed bar, knife bevel 20°, knife angle 90° (0° clearance), lead 0.030 in. (0.76 mm), and gap 10 pet less than feed.

Table 9.—Lathe settings with a fixed bar and a variable lead ^

Feed (veneer thickness) Lead Gap Exit gap In. Mm In. Mm In. Mm In. Mm 0.010 0.25 0.005 0.13 0.009 0.23 0.010 0.25 .032 .81 .010 .25 .029 .74 .031 .79 .042 1.07 .012 .30 .038 .97 .040 1.02 .0625 1.59 .017 .43 .056 1.42 .058 1.47 .100 2.54 .024 .51 .090 2.29 .093 2.36 .125 3.17 .030 .76 .112 2.84 .115 2.92 .1875 4.76 .043 1.09 .169 4.29 .173 4.39 .250 6.35 .056 1.42 .225 5.71 .230 5.84

1 Fixed bar, knife bevel 21°, knife angle 90° (0° clearance), 1 ead changing with veneer thickness (13), , and gap 10 pet less than feed.

Table 10.—Lathe settings with a roller bar and a fixed lead ^

Feed (veneer thickness) Lead Gap Exit gap In. Mm In. Mm In. Mm In. Mm 0.0625 1.59 0.085 2.16 0.056 1.42 0.062 1.57 .100 2.54 .085 2.16 .090 2.29 .094 2.39 .125 3.17 .085 2.16 .112 2.84 .114 2.90 .1875 4.76 .085 2.16 .169 4.29 .167 4.24 .250 6.35 .085 2.16 .225 5.71 .220 5.59 1 5/8-in.-diameter roller bar, knife bevel 20°, knife angle 90° (0° clearance), lead 0.085 in. (2.16 mm), and gap 10 pet less than feed.

Table 11.—Lathe settings with a roller bar and a variable lead ^

Feed (veneer thickness) Lead Gap Exit gap> In. Mm In. Mm In. Mm In. Mm 0.0625 1.59 0.068 1.73 0.056 1.42 0.056 1.42 .100 2.54 .075 1.90 .090 2.29 .090 2.29 .125 3.17 .079 2.01 .112 2.84 .112 2.84 .1875 4.76 .089 2.26 .169 4.29 .169 4.29 .250 6.35 .100 2.54 .225 5.71 .225 5.71 ' 5/8-in.-diameter roller bar, knife bevel 2V, knife angle 90° (0° clearance), gap equal exit gap equal 10 pet less than feed.

62 have a lead or vertical-opening adjustment. slightly nick the blade. It is, therefore, good This distance is built in the lathe to be about practice to lightly hone the knife after setting 0.020 inch (0.5 mm). It coincides with the lead the lead. suggested by Fleischer for cutting veneer about Vu inch (2 mm) thick. Setting the Gap The second bar adjustment is the gap or All agree that the bar edge should be set horizontal opening. This is the distance from above rather than at or below the knife edge. the leading edge of the pressure bar to a plane It is also generally agreed that the distance the extended from the ground surface of the knife. bar is set to lead the knife must be the same at Some experienced operators like to bring the all points along the knife edge. edge of the bar to the same plane as the knife The common method of checking this opening edge. Then by feeling with the thumb, they can is to insert a feeler gage of the proper thick- tell if there are any spots where the bar is ness in the lead (fig. 22) between the knife ahead or behind the knife edge. These local edge and the bar. When the feeler gage is per- spots are brought in line with the push-pull pendicular to the ground face of the knife, the screws at the back of the bar. Once the bar is opening is the same as the thickness of the "fit" to the knife, it is retracted to give the gage. After the bar is set this way at both ends, desired opening or gap and clamped. it should also be checked at other intervals We prefer to use instruments to help make along the knife. Some lathes have push-pulls this critical setting. Two such instruments are so the bar can be warped locally to make the described by Fleischer (19) and Feihl and lead or vertical opening uniform across the Godin (15). Both are essentially dial-microm- lathe. However, if the knife and bar are ground eter depth gages that use the ground surface straight and the knife bed and bar bed are also of the knife as a reference and measure to the straight, any local adjustment of the lead edge of the bar. To automatically position the should be minimal. Use of a feeler gage may measuring pin, Fleischer (,19) suggests that

M 139 942 Figure 22.—Adjusting the lead of the pressure bar with a feeler gage. The lead of the bar is moved until a feeler gage of the desired thickness is at a right angle to the face of the knife when the gage is inserted in the opening between the knife and the bar.

63 M 139 940 Figure 23.—Measuring the gap between the knife and pressure bar edge. Measurements are chalked on the nose- bar casting and any deviations greater than 0.001 inch removed with the push-pull adjustment of the bar. the instrument rest on the top of the pressure rected by the push-pull screws at the back of bar and on the ground face of the knife (fig. the bar. For accurate cutting, the gap should be 23). within ±0.001 inch (0.025 mm) at all posi- While one man holds the instrument in con- tions. tact with the knife and the movable sensing The actual value of the gap will depend on pin against the leading nosebar edge, a second the thickness of veneer and somewhat on the man advances the bar until the correct gap or species being cut. A figure commonly quoted is horizontal opening is indicated. When advanc- for the gap to be 20 percent smaller than the ing the bar, the adjustment should always thickness of veneer being cut. Experiments at be made to take the play out of the adjusting the U.S. Forest Products Laboratory indicate screws. First the two ends are checked. If they this results in high compression of the wood do not indicate the same opening, then they by the nosebar. It would only be used when cut- must be brought to the same position with the ting thin veneer from an easily compressible adjusting screws at each end of the pressure species that is resistant to damage by scraping bar bed. Assuming the knife and bar were the nosebar over the wood surface. ground straight and were not warped when It is possible the 20 percent figure may have mounted on the lathe, the gap should now be been derived from measurements on lathes that the same across the lathe. However, since this had some looseness or play and not correcting is one of the critical lathe settings, we routinely for the looseness. check the opening or gap at 4-inch intervals When the pressure bar is set as described along the bar. The value of each reading is earlier we have found a compression of 10 to chalked on the casting holding the pressure bar. 15 percent to be good for cutting veneer from Any gradual bends or humps in the bar are i/io to Vs inch (1.6 to 3.2 mm) thick. Twenty per- then plainly visible. Local deviations are cor- cent compression may be satisfactory when

64 cutting thinner veneer. Higher compression gap or horizontal openings between the knife (smaller gap or horizontal opening) may re- and bar to be between 0.029 and 0.032 inch sult in tighter veneer; it may also cause the (0.725 and 0.800 mm). In effect, the bar is then veneer to be thinner than the knife feed and compressing the wood just ahead of the knife cause damage to the tight side, such as shell- edge 0.004 to 0.007 inch (0.1 to 0.175 mm). ing of the grain on susceptible species like Face veneer producers sometimes set the bar western redcedar and redwood. to compress the wood only 0.001 or 0.002 inch. The advantage of using instruments to meas- When slicing thicker veneer such as Vs (0.125) ure the knife angle and pressure bar settings inch (3.25 mm), the bar may be set to leave a is that the setup can be readily duplicated. gap of 0.115 inch (2.95 mm), or 0.010 inch When experience shows that a certain setting (0.25 mm) less than the feed. is good for cutting a given thickness of veneer As with the lathe, more compression (slightly from a given species at a given temperature, smaller openings) can be used when cutting then the information should be recorded and low-density woods than when cutting high- the exact processing conditions duplicated when density woods. this item is produced again. Setting Roller Pressure Bar on Lathe (by Lead and Gap) Setting Fixed Pressure Bar on Slicer (by Lead and Gap) The roller bar is most commonly used when rotary-cutting western softwoods ¥12 to ^AG inch The slicer bar is ground and set by the same (2.1 to 4.8 mm) in thickness. It is not suitable method as described for setting the fixed bar on for cutting veneer thinner than Mc inch (1.6 the lathe. The difference comes in the actual mm). The reason is that the pressure should value of the settings. On the lathe, the lead or be applied against the bolt just ahead of the vertical opening may be set at various openings knife edge. When cutting veneer thinner than such as 0.010 inch (0.25 mm) for %o-inch (0.5 i/iß inch (1.6 mm), a roller bar set at a fixed mm) veneer to 0.030 (0.75 mm) for Vs-inch bar lead would over-compress the veneer after (3.2 mm) veneer. On the slicer, the lead or it is cut by restricting the throat between the vertical opening is generally set at about 0.030 roller bar and the knife. This restraint may inch (0.75 mm). We have cut veneer of satis- cause the veneer to jam and break. factory quality from Vioo to % inch (0.25 to 6.3 In industry practice, %-inch- (15.9 mm) di- mm) in thickness with this lead. A smaller lead ameter roller bars are generally set with a lead such as 0.020 inch (0.5 mm) can be used when of V16 (0.062) inch (1.6 mm) or more. From cutting i/is-inch (0.9 mm) and thinner veneer. theoretical considerations and laboratory ex- However, this smaller lead may result in more periments, Feihl, Colbeck, and Godin (13) splinters breaking off at the end of the cut and recommended a roller bar lead or vertical gap more chance that splinters will become jammed of 0.085 inch (2.16 mm) when cutting Douglas- between the knife and bar, causing rub marks fir Vio to 1/4 inch (2.54 to 6.35 mm) in thickness. on the veneer. They also describe an instrument for measur- Not as much pressure can be applied with the ing the lead of a roller bar. nosebar on a vertical operating face veneer Lathe settings for several veneer thicknesses slicer as can be applied on a lathe. The knife using a fixed lead are shown in table 10. and pressure bar rest on half bearings, permit- The gap is set much the same as with a fixed ting the knife and bar to be offset to clear the bar. That is, good results are obtained by com- ñitch on the upstroke. If the pressure bar is pressing the wood ahead of the knife about set for excessive pressure against the flitch, it 10 to 15 percent of the veneer thickness. This will cause the knife and bar carriage to rock on varies with species, wood density, and veneer the half bearing; the result is poor veneer and thickness as discussed under the fixed pressure possibly damage to the slicer. bar. The gap or horizontal opening can be set When slicing ^As-inch (0.036-in.) (0.9 mm) and checked with a depth gage reading to veneer, we have found the range of satisfactory 0.001 inch (0.025 mm).

65 Setting Roller Pressure Bar the bar. They report that the method elimi- (By Gap and Exit Gap) nates play in the horizontal mechanism; pro- Collett, Brackley, and Gumming (7) suggest vides a direct measure of pressure against the that lathes having a roller bar be set by gap bar and so gives the operator good control of and exit gap. They comment that, for veneer the setting; and finally that the veneer pro- thicknesses from Mo to % inch (2.54 to 6.35 duced was equal in quality to veneer produced mm), the literature indicates that the gap and with a bar set to fixed stops. The method is exit gap can be the same. This simplifies the being tried commercially. recordkeeping as only one value needs to be recorded for each veneer thickness of each Possible Ways to Generalize Setting of species. They recommend use of a depth gage to Lathe and Slicer measure the gap and a feeler gage to measure Optimization of veneer peeling or slicing may the exit gap. The amount of compression they require different knife and pressure bar settings suggest at both the gap and exit gap is 10 to for each specific cutting situation. However, it 20 percent of the veneer thickness. Table 11 would be convenient to have one knife setting shows some settings where the gap and exit that could be used to cut veneer of any species gap are the same. into any thickness from ¥32 to % inch (0.8 to 6.3 mm). Similarly, it would simplify pressure Setting Fixed Pressure Bar bar settings if one lead could be used for cut- (By Lead and Exit Gap) ting all veneer. From an examination of the Lead and exit gap are suggested by Fondron- literature and our own experience, it is possible nier and Guillerm (21) as the openings to be to do this. measured when setting a lathe with a fixed bar. They list the lead changing in a regular man- Generalized Knife Settings ner with veneer thickness as follows : The knife settings specified in figure 24 are broadly applicable, and may be particularly Veneer Thickness Lead or Vertical Opening valuable as a starting point for cutting un- (in.) (mm) (in.) (mm) familiar species. 0.039 1 0.020 0.5 .078 2 .024 .6 The knife should be ground to a 21° bevel .118 3 .028 .7 with 0.002-inch (0.05 mm) hollow grind. The .157 4 .031 .8 knife angle can be set to 90° 30' or, stated .197 5 .035 .9 .236 6 .039 1.0 another way, with %° clearance angle. For lathes having an automatic change of knife They suggest the exit gap should be 10 to 20 angle with change in bolt diameter, the knife percent less than the veneer thickness. Further can be set at 90° 30' when it is 12 inches (30 they recommend that feeler gages be used to mm) from the spindle center. This knife set- measure both the lead and exit gap. ting can be used to cut veneer V¿2 to % inch (0.8 to 6.3 mm) in thickness from any species Setting Gap by Pressure Rather Than to on the slicer or on the lathe from bolt diameters Fixed Stops of 24 inches (60 cm) to a 6-inch (15 cm) core. During rotary cutting of veneer, the force against the pressure bar may vary as much as Generalized Setting of a Fixed from 10 to 500 pounds per lineal inch (178 to Pressure Bar 8,900 kg/m) of contact with the wood (45), The pressure bar should be ground to have Feihl and Carroll (12) adapted a research an included angle to 75°. This results in the lathe to allow the bar to float and maintain the woodwork piece being compressed along a gap by pressure delivered by a cylinder and plane approximately 15° from the cutting direc- piston acting against the bar frame. In other tion. The edge of the bar that contacts the words, they set the lead to stops but allowed wood should be rounded to an edge having a the gap to be determined by the force against radius of about 0.015 inch (0.3 mm).

66 KNIFE AND FIXED BAR KNIFE AND ROLLER BAR M 144 168 Figure 24.—Knife and pressure bar settings of general applicability are specified in terms of the diagram. These settings might be used to cut veneer from 1/32 to V^. inch in thickness.

Symbol Generalized Settings Symbol Generalized Settings A Knife angle = 90° 30' E Pressure bar bevel = 75° B Knife bevel = 21° with 0.002-inch F Gap = 90 percent of veneer thickness hollow grind (10 pet compression) C Clearance angle = 30' (i/2°) G Exit gap = Gap = 90 percent D Lead = 0.030 inch for fixed bar or of veneer thickness (roller bar) 0.085 for %-inch-diameter roller bar H Nosebar compression angle = 15° (fixed bar)

67 The lead of the fixed pressure bar ahead of Summary of Generalized Lathe and the knife edge can be 0.03 inch (0.75 mm) for Slicer Settings both the lathe and the slicer. The gap from the edge of the pressure bar Suggested ''universal" lathe and slicer set- to the plane of the ground face of the knife can tings—listed in figure 24—are not optimum be 90 percent of the thickness of the veneer settings, but they should permit cutting veneer being cut. Veneer Vs2 to V^ inch (0.8 to 6.3 mm) of moderate quality from any species into any in thickness and of various species can be cut thickness from V32 to % inch (0.8 to 6.3 mm). with these fixed pressure bar settings (fig. 24). (The roller bar is not satisfactory for use when cutting veneer thinner than Vw in. (1.6 mm).) In general, excluding the extreme ranges of Generalized Setting of Roller specific gravity, one species of wood acts much Pressure Bar like another and the veneer cutting process The generalized settings for lathes with a does not change abruptly within the range of roller pressure bar are for cutting veneer Vir, to thickness from y32 to % inch (0.8 to 6.3 mm). % inch (1.6 to 6.3 mm) in thickness. The lead The settings listed with figure 24 will gen- of the roller bar should be 0.085 inch (2.16 erally result in a moderately tight cut. If tighter mm). That is, the center of the 5.8-inch- (15.9 and smoother veneer is desired, smaller open- mm) diameter roller bar should lead the knife ings between the knife and pressure bar may edge by 0.085 inch (2.16 mm). The comparable be used. Lathes having automatic pitch adjust- figure for the fixed bar is 0.030 inch (0.75 mm) ment could be set to have a knife angle of 91° (fig. 24 and tables 8 and 10). at a bolt diameter of 36 inches (91 cm) and a knife angle of 89° 30' at a bolt diameter of 6 An Alternate Generalized Setting of inches (15 cm). Ideally, the rate of change of Roller Pressure Bar the knife pitch should be greater at the smaller Collett, Brackley, and Gumming (6) describe diameters. A smaller fixed pressure bar lead setting a roller bar with the gap and exit gap such as 0.020 or 0.015 inch (0.5 to 0.4 mm) can equal. As with the rigid bar, a generalized set- be used for cutting Vio-inch (1.6 mm) and thin- ting would be to have the gap and exit gap ner veneer. both 90 percent of the thickness of the veneer being cut (fig. 24 and table 11). Positioning Bolts and Flitches For maximum yield of rotary veneer, it is Generalized Setting of the Gap by Pressure essential that bolts be chucked in the geometric Feihl and Carroll (12) report that pine center. If the bolts are chucked eccentrically as veneer that is Vio to VG inch (2.5 to 4.2 mm) in little as ¥2 inch, the recovery of veneer can be thickness can be cut satisfactorily with the reduced significantly. H. C. Mason, an industry pressure on a floating roller bar of about 60 consultant, stated in 1972 that use of bolt- pounds per linear inch (1.070 kg/m) of bar diameter-measuring instruments and a mini- contacting the wood bolt. They further con- computer controlling a lathe charger to pre- clude : ''It is not impossible that in some mills cisely center the bolt in the chucks, will result (when all species are fairly similar and veneer in at least a 7-percent increase in recovery of thicknesses are in the same range) it would be veneer for a typical Douglas-fir veneer plant. practical to use one pressure setting." The way a flitch is mounted on the slicer table has little effect on yield, but it can aflfect the smoothness of the veneer (S9), An eccentric flat-cut flitch should be dogged with the pith toward the start of the knife cut. A quartered flitch should be turned 180° when the cut ap- proaches the true quarter. These and related phenomena are discussed in detail in (39).

68 CONVEYING AND CLIPPING VENEER

Conveying Veneer from Lathe A German machinery manufacturer recently announced a system to reel sliced veneer by first As veneer comes from the lathe, it may be applying string to the ends of the veneer sheets manually pulled out on a table, but more gen- as they come from the slicer. The string then erally it is moved to long trays in line with the "leads'' the veneer onto the reel where it can clippers or is reeled. then be stored before unreeling into a dryer. The tray system is most common in both softwood and hardwood plants. As the veneer comes from the lathe, a short tipple directs un- Clipping Green Veneer usable veneer to a waste conveyor. Usable Veneer stored on trays is fed to one or more veneer is directed into one of the trays with clippers. In a typical installation, with six trays belts synchronized to the lathe speed. After one from a lathe, three trays would feed to one clip- tray is full, the veneer is broken or cut, and the per and the other three to a second clipper. A veneer directed to another tray. This must be modern clipper has some sensing and measuring done carefully to prevent the veneer ribbon device so veneer can be clipped to nominal 4-foot from being folded and split. (1.2 m), 2-foot (0.6 m), or random widths. The second mechanical means of conveying Random widths may be generated when defects veneer from the lathe is with a reel. The reel such as knots and splits are clipped from the system works best with Vs-inch (3.2 mm) and veneer ribbon. An accurate sensing device thinner hardwods cut from sound bolts. Like coupled with the clipper soon pays for itself by the tray system, the first unusable veneer is greater yields of usable veneer. The green veneer directed to a waste conveyor. Then the usable is then sorted by widths, grades, and possibly roundup is collected on a short tray or table. by sapwood and heartwood in preparation for Finally, when a sound ribbon veneer comes drying. from the lathe, it is tacked to a reel and the Reeled veneer is stored in racks and unreeled veneer reeled up as it is peeled. The speed of just ahead of the clipper. The clipping opera- the reel is synchronized with the lathe. The tion is much the same as that described for veneer is reeled with the loose side out. veneer stored on trays. One limitation of reeled Combination tray and reeling is popular with veneer is that, if it is cut from hot bolts, it some plants peeling species like lauan. The bet- should be clipped before the veneer cools and ter grades are cut into thin face stock and sets in a curved shape. reeled. Lower grades are cut into thicker core Flitches of green sliced veneer sometimes stock and conveyed on trays. have defects clipped out or are trimmed before drying. Packs about Vi-inch (6.3 mm) deep are Conveying Veneer from Slicer clipped together as a book. The green clipping saves drying of material that will not be used. It is important to keep the sliced veneer sheets in consecutive order. In many plants, two men turn the veneer over as the sheets come from Clipping Dry Veneer the slicer and stack them consecutively with the Veneer on trays or on reels is sometimes fed loose side up. In some cases, a short conveyor to the dryer in a continuous ribbon. As the takes the veneer from the slicer to a position veneer comes from the dryer, it is clipped to where it is more convenient to stack it. Some size. This system reportedly results in less European plants automatically convey the sliced waste and split veneer. One dryer manufac- veneer to a veneer dryer. Dryer capacity should turer states that drying of a continuous ribbon be sized for the wood veneer species, thickness, will result in at least a 4-percent increase in and production rate of the slicer. recovery of dry veneer.

69 VENEER DRYING

An essential part of the veneer-producing veneer sheets, which tend to dry faster than the process is to dry the veneer. The amount of this bulk of the sheet. It may also be a factor in drying varies widely. Products that require a curly-grained or other figured veneer where at minimum of drying—such as bushel baskets least partial end grain is exposed on the broad and fruit containers—may bring the veneer be- surface of the veneer. As these areas dry faster low a moisture content at which it will mold than surrounding straight-grain areas, they can (about 20 pet). On the upper extreme is drying cause stresses and buckling in the veneer sheet. of softwood veneers that are to be glued with The difference in drying rates between radial a phenolic hot-press glue, in which case the and tangential surfaces is small but may show veneer must be 5 percent or lower in moisture up. Quarter-sliced veneer will take slightly content. In between are such products as deco- longer to dry than rotary-cut veneer of the rative face veneer, generally dried to 8 to 10 same thickness, and flat-sliced veneer may dry percent moisture content, and commercial hard- slower on the near-quarter edges than in the wood veneers that are to be glued with a urea flat-grain area at the center of the sheet. glue, in which case 6 to 8 percent moisture con- The moisture in the veneer naturally affects tent is desirable in the veneer. In all cases, a the total drying time, as expressed in several major criterion is to dry the veneer at the lowest ways. Veneer from butt logs may have higher total cost. moisture content than top logs. For example, Because most veneer operations are set up in the difference in moisture content of the heart- a straight-line production system and the pro- wood of redwood from different logs may be as duction from the lathe and slicer is very high, much as 2 to 1. Furthermore, the wetter heart- it is generally necesary to have a fast drying wood veneer requires significantly longer dry- system. Dried veneer should: (1) Have a uni- ing time than drier heartwood of the same form moisture content; (2) be dried without species. buckle or end waviness; (3) be free of splits; Comstock (8) indicates that density of the (4) be in good condition for gluing; (5) have veneer may be another factor in total drying a desirable color; (6) have a minimum of time. The denser wood heats more slowly than shrinkage; (7) avoid collapse and honeycomb; less dense wood and requires more total calories and (8) have a minimum of casehardening. to heat and dry. (Veneer is casehardened when the outer layers The differences between the sapwood and are in compression and the center or core is in heartwood may be factors with some species and tension.) not with others. Bethel and Hader (3) report that the sapwood of sweetgum will dry 25 to 30 Some Veneer Properties That Aflfect percent faster than the heartwood of sweetgum. Drying The difference is attributed to the difference in Factors that affect drying of veneer include permeability of the sapwood and the heartwood. both the wood itself and the drying conditions. This same phenomenon has been observed at the An obvious factor is the thickness of the U.S. Forest Products Laboratory when drying veneer. Thicker veneers dry more slowly than veneer of túpelo and other hardwoods like over- thin veneers. A modification of this is variation cup oak. In contrast, Comstock (8) reports that in veneer thickness from the nominal thickness. drying time in a jet dryer does not depend on Commercial %-inch (3.2 mm) veneer will often whether the veneer is heartwood or sapwood. vary ±0.008 inch (0.2 mm) or more in thick- Similarly, there is a lack of agreement on the ness. The thicker portions of the veneer take effect of species on veneer drying. Fleischer longer to dry than the thinner portions and con- (18) found that redwood and sweetgum heart- tribute to a nonuniform final moisture content. wood dried at a slower rate than yellow-poplar A second factor is the grain direction on the heartwood. Bethel and Hader (3) also found surface of the veneer. End grain dries several differences in the drying of different species. times faster than tangential (fiat) grain. End- Comstock (8) and Fleischer (18) indicate that grain drying is significant at the ends of all veneer drying is controlled to a large extent by

70 the rate of heat transfer to the veneer. Fleischer matched material dried in kiln. The least qualifies this by saying that this controlling buckled will be veneer dried between flat hot- factor is a function of veneer thickness and also plates. to some degree of veneer species. Comstock (8) Temperature and drying time are factors that states that differences between species and be- can affect the rate of drying. For example, tween hardwood and sapwood are not important Vg-inch (3.2 mm) heartwood of Douglas-fir dried independent variables aside from their effect on at 250° F (121° C) may require 20 minutes in the veneer density and moisture content. He the dryer. The same kind of veneer dried at developed a general equation for the time re- 320° F (160° C) may dry in 10 minutes. In- quired to dry veneer in a jet dryer. He was, creasing the drying temperature to 400° F therefore, interested in generalities that could (204° C) may reduce this drying time to about be used for any given species. Bethel and Hader 6 minutes. Douglas-fir heartwood veneer has (3) concluded that the drying rate of veneer been dried in 2-I/2 minutes by using a drying may be controlled by moisture diffusion. temperature of 550° F (288° C). Such a high From the literature then, it appears that the drying temperature may, however, lead to prob- rate of heat transfer to veneer is an important lems in gluing the veneer. factor in the rate of veneer drying. However, Another factor which is universally agreed to diffusion, at least in part, controls rate of dry- affect the drying rate is the air velocity across ing in %-inch (3.2 mm) and thicker veneer of the veneer surface. In loft drying, air move- the impermeable species such as sweetgum ment is very slow from convection currents. heartwood. Veneer dried in a kiln might be subject to air Reaction wood—tension wood in hardwoods velocities of several hundred feet per minute. and compression wood in softwoods—shrinks This higher air velocity, together with the more longitudinally than typical wood of the higher temperatures used in the kiln, greatly the same species. As a result, sheets of veneer accelerates the drying. containing streaks of tension wood or compres- Prior to 1960, most mechanical veneer dryers sion wood tend to buckle during drying. had air circulation either in the longitudinal Do breaks (knife checks) in the veneer dur- direction of the dryer or across the width of the ing cutting have any effect on drying? Experi- dryer. Typical air velocities in such dryers were ments at the Forest Products Laboratory do not about 600 feet (180 m ) per minute. Most me- show any difference in the drying rate of i/iß- chanical dryers made after 1960 have the air or Vs-inch (1.6 or 3.2 mm) loosely cut and impinging directly onto the face of the veneer tightly cut sapwood veneer of sweetgum and through slots or orifices. The air velocity is in yellow birch dried at 200° to 350° F (93° to the range of 2,000 to 10,000 feet (600 to 3,000 177° C) with an air velocity of 600 feet (180 m) m) per minute. This very high air velocity tends per minute. The loosely cut veneer was easier to break up any boundary layer at the veneer to flatten after drying. surface and greatly improves heat transfer. As a result, with a given dryer temperature, thin Some Dryer Conditions That Can Affect veneer will dry about one-third faster in a jet Veneer Drying dryer than in a mechanical dryer having longi- In general, dryers are operated to hold the tudinal or cross circulation air movement. veneer flat and transfer as much heat as pos- The fastest heat transfer is by conduction. In sible to the veneer during drying. general, with a given dryer temperature, veneer The importance of holding the veneer flat can dried between heated platens requires less dry- be judged by comparing matched sheets of ing time than veneers in a dryer that depends veneer dried with various amounts of restraint. on air circulation to transfer the heat. The dry- In general, buckle will be greatest in the veneer ing occurs fastest when the metal cauls are per- hung from the ends and allowed to dry at forated to allow moisture to escape while main- ambient room conditions. Next will be veneer taining high heat transfer from the hot plates. restrained by stickers and dried in a kiln. The roller conveyor or wire-mesh conveyor in Veneer dried in a mechanical dryer with a roller conventional mechanical veneer dryer aids in or wire-mesh conveyor will buckle less than the drying by transferring heat by conduction

71 to the veneer surface. Some investigators have most satisfactorily with a restraint weight of reported that the heat transfer from the rolls about 5 pounds per square foot (24 kg/m-) may be as much as 20 percent of the total heat when drying thin face veneer. In a roller dryer transferred to the veneer. the rollers are generally hollow tubes which This heat transfer from the rolls is very- rest directly on the veneer. Both the roller con- obvious when comparing the drying rates of veyor and the wire-mesh conveyor can con- veneer through an essentially empty dryer and tribute to drying by conducting heat directly to one in which the conveyor is full of veneer. In the surface of the veneer. Longitudinal, cross- the full dryer, the rolls are cooled by the wet circulation, and impingement air movement are veneer and the required drying time for a given used in these progressive dryers. The method final moisture content increases. This means the most commonly used in new veneer plants today first veneer through an empty dryer will emerge is the jet dryer with the air impinging on the much drier than veneer coming from a full veneer surface at velocities of 2,000 to 10,000 dryer. If the drying time is set according to the feet (600 to 3,000 m) per minute. first veneer through the dryer, the time will be Some veneer is dried in progressive kilns. too short, and veneer coming from a full dryer These kilns are operated at temperatures below will be much higher in moisture content. 212° F (100° C) and, consequently, the relative The relative humidity in a kiln can be used to humidity and equilibrium moisture content of control the final moisture content of the veneer. the veneer can be controlled. Control of the final The relationship of wet-bulb and dry-bulb tem- moisture content and production of veneer that peratures to the final equilibrium moisture con- is easily glued are two of the main advantages tent of the wood is shown in figure 25. The of the progressive kiln. ability to control the final moisture content of Some products, like baskets, are assembled the veneer is one of the main advantages of the from green veneer and then dried. Usually dry kiln. heated tunnels with conveyors are used to dry Most veneer is dried in mechanical dryers at veneer to about 20 percent moisture content to temperatures above 250° F. At these higher prevent mold. temperatures, Fleischer reports that relative A few veneer plants use progressive platen humidity has no effect on the drying rate (IS). dryers. Many users of face veneer redry their As a matter of interest, the calculated equi- veneer in a platen dryer. librium moisture content of wood in saturated A rather unique face dryer made in Germany steam at 220° F (104° C) is about 11 percent. consists of perforated drums, with a partial At 240° F (116° C) it is about 5 percent. Re- vacuum inside the drums. The vacuum holds cent experiments show that veneer steamed at the veneer against the heated drum and re- 220° to 240° F in a kiln or in a hot press will portedly works satisfactorily with relatively come to the desired final moisture content. Dry- thin veneer. The dryer does not seem well ing veneer to a controlled final moisture content adapted for veneer thicker than y2s-inch (0.9 should reduce degrade, reduce shrinkage, and mm). provide a superior surface for gluing. An all-infrared dryer has been used com- mercially on the West Coast, but its use was Types of Veneer Dryers discontinued because of high drying costs. By far the most common veneer dryer is the Recently banks of gas-fired infrared heaters direct-fired or steam or hot water-heated pro- have been placed at the green end of a few gressive conveyor type. The roller conveyor is dryers used with softwood veneer for construc- used most commonly with rotary-cut veneer. A tion plywood. They boost the temperature to wire-mesh conveyor is used for drying continu- reduce the drying time of thick sapwood veneer. ous ribbons of rotary-cut veneer and for sliced Similarly, high-frequency and microwave en- and half-round veneer. It permits feeding the ergy have been used as a part of drying systems veneer sidewise so that the sheets can be kept to equalize moisture content at the end of the in sequence for matching, in contrast to the drying cycle. These methods have not been gen- roller dryer where the sheets are fed endwise. erally used because of high equipment and The wire-mesh conveyor is reported to work power costs (59),

72 Figure 25.—Lines of constant equilibrium moisture content.

73 Drying veneer between perforated cauls in a Keep the dryer vents as nearly closed as hot press has been shown experimentally (30) practical. This will reduce the energy consumed to be a fast way to dry flat veneer. and reduce veneer dryer emissions. If condensa- tion and haze in the building become trouble- Veneer Drying Emissions some, open the vents the minimum amount A factor of current interest is veneer dryer needed to correct the problem. emissions and whether they contribute to air In general, operate the dryer with the maxi- pollution. Recent studies indicate the opacity of mum air circulation possible. It may sometimes the plume from veneer dryers ranged up to 82 be necessary to reduce the air velocity to pre- percent with an average of 21 percent (1), vent overdrying and splitting of very thin Opacity is judged visually by qualified raters. veneer. Rating is in 20-percent increments similar to Keep the dryer as full of veneer as possible. the Ringelmann Smoke Scale. Dryer schedules should be based on a full dryer The State of Oregon passed a law in 1972 operating at a steady temperature and air limiting opacity of plumes from existing veneer movement. dryers to 20 percent and from new dryers to Segregate green veneer by required drying 10 percent. time. The green veneer sorts should be by The opacity of the plume can be reduced by veneer thickness, species, and—for many soft- using stack velocities over 2,000 feet (600 m) woods—by sapwood and heartwood. Doubling a minute. While this may pass the opacity the veneer thickness will more than double the limitation, it is costly because it results in a drying time. Sapwood of species like Douglas- large heat loss. Also, it does not cut down on fir requires about twice as much drying time as pollution. heartwood veneer. Heartwood and sapwood of Another approach is to filter the stack gases many hardwoods dry in about the same time. at high velocity through a fiberglass mat. This Veneer containing both sapwood and heartwood system can reportedly reduce the average opac- or wet streaks in the heartwood should be dried ity to 5 percent or less (5). on the sapwood schedule. Still another approach is to recirculate the The veneer drying time should be regulated air in direct-fired dryers through a heated duct by the kind of veneer being fed in the green at 1,200° F. In one-half second the hydro- end. It is tempting for the dryer operator to carbons are incinerated and visibility of stack change the drying time from the dry end, de- emissions reduced accordingly (5). Heat of pending on whether the emerging veneer seems combustion of the hydrocarbons is recovered too wet or too dry. If he does, there may be a by a heat exchanger to lower the total fuel constant shifting of drying times and a cor- needed to operate the system. responding shifting in the average moisture content of the veneer out of the dryer. A better Applied Drying Suggestions for method is to carefully determine the proper Mechanical Dryers time to dry veneer of a given thickness, species, Dry the veneer as soon as practical after cut- and sapwood or heartwood and use this sched- ting to minimize end splits, oxidation stain, ule when similar veneer is dried again. mold, and blue stain. This is particularly im- Even when the best dryer schedules are main- portant for light-colored wood. tained, there will be a range of moisture con- To minimize drying time, operate the dryer tent in the emerging veneer. Consequently, it is at the maximum temperature consistent with very desirable to have a constant electronic good glue bonds and wood color. In general, this check of the moisture content in the veneer. will be about 400° F (204° C) at the green end Veneer having wet spots can be pulled sepa- and 360° F (182° C) at the dry end of the rately. After standing overnight or longer, the dryer. If gluing or veneer color are problems, veneer can be rechecked for high moisture con- lower the dryer temperature. Decreasing the tent and wet pieces redried. dryer temperature by 100° F (38° C) (for ex- If automatic moisture-detection equipment is ample, from 350° to 250° F (177° to 121° C) ) not available, then the veneer out of the dryer will approximately double the drying time. should be checked regularly with a hand-oper-

74 ated moisture meter. When such meters are will be less noise from static electricity, and the calibrated for a given species and make firm veneer may be more free of end waviness and contact on cool veneer, they are quite accurate buckle. from about 6 to 15 percent moisture content. All veneer should be cooled and held flat as An experienced dryer operator can some- it comes from the dryer. Cool veneer is less times tell in general the veneer is drying by likely to buckle and will not contribute to pre- subjective methods. When veneer is being over- cure of gluelines. dried, static electricity makes the dryer snap The dried veneer should be neatly stacked on and pop. Overdried veneer may be hotter to flat skids and the top of the pile weighted. touch and in extreme cases may be darkened. Flitches of sliced veneer should be promptly Underdried veneer will be cool to touch, there strapped in flat crates.

QUALITY CONTROL browning of a freshly cut surface of an apple. Undried Veneer Enzymes, moisture, favorable temperatures, The quality of veneer is affected by log qual- and air are factors in this color change. ity, by the care used in storing the logs or Probably the best way to control this stain flitches, by heating the wood prior to cutting, is to dry the veneer promptly after cutting so and by the mechanical condition, setup, and the surface is dried before oxidation takes operation of the lathe or slicer. place. Holding wet veneer over a weekend is Quantitatively five factors should be checked likely to cause stain on susceptible wood species. at regular intervals : Stain, uniformity of thick- Another control method is to heat the logs ness, roughness of the veneer surface, breaks sufficiently to inactivate the enzymes present in in the veneer, and buckle or other distortions of the wood. This generally means heating the logs the veneer. for 2 days at 160° F or higher rather than lim- iting heating to overnight. We have been told Control of Stain that running the veneer through boiling water Stain on veneer may be due to fungus, oxida- as soon as it is cut may prevent the stain. tion, or contact of the wet wood with iron or When wet wood comes in contact with iron steel. or steel, it reacts to form a blue-black stain. The Blue stain is the most common fungus stain stain becomes worse the longer the contact and that occurs readily in the sapwood of most spe- the hotter the wood. It may be particularly cies if unprotected logs are stored during warm prevalent on woods like oak that have a high weather. The best control is rapid processing of tannin content, and is very noticeable on light- the logs or storage of the logs under water or colored wood like the sapwood of maple. Such under a water spray. If water or water spray stain is not particularly important for uses like is not available, end coating the logs is bene- construction plywood but is very objectionable ficial. on decorative face veneer. Oxidation stain is generally a yellow or tan Control methods include keeping the knife stain that may penetrate from the ends of un- and pressure bar as clean as possible; heating protected logs during summer storage. Like the knife and pressure bar to reduce condensa- fungus stain, it can be prevented by rapid proc- tion; lacquering the knife and pressure bar so essing of the logs or by storing logs under water that only the extreme edges have exposed steel or under a water spray. End coatings are also that can stain the wood ; using stainless metals helpful. for the pressure bar and knife ; using a double Oxidation stain may also occur on the surface bevel on the slicer knife so the heel of the slicer of veneer sheets between the time they are cut knife cannot rub against the flitch; using a and dried. A common example is the yellow greater knife angle (more clearance) so the stain that may develop on birch or maple sap- heel of the slicer knife does not contact the wood. The stain is sometimes compared to the flitch ; and using less nosebar pressure.

75 M 139 943 Figure 26.—Micrometer for measuring veneer thickness to 0.001 inch.

Control of Veneer Thickness For quality-control purposes, it would prob- Uniform veneer thickness is desirable for ably pay to have a comparator such as de- production of high-quality glue bonds in ply- scribed by Bryant, Peters, and Hoerber (4). wood, for minimizing show-through of the core, The size of the anvil or contacting surface and for producing panels to a specified thick- should be about 1/2 inch (12.7 mm) in diameter ness. and the weight on the top anvil about 0.66 Since uniform veneer thickness is so im- pound (300 g). When checking thickness of portant, it should be checked on a regular basis. heavy veneer, we have found an air-operated As a minimum, at the green end, the foreman cylinder with adjustable contact pressure and and the lathe or sheer operators should have anvils about 2 inches (5 cm) in diameter to be hand micrometers that read to 0.001 inch (0.025 fast and accurate (fig. 27). mm) (fig. 26). They should be encouraged to The tolerance permitted in green veneer will check veneer thickness at the start of each depend in part on the end use. For exacting shift, at each knife change, after any change in end uses, this tabulation may be a guide: thickness being cut, and randomly at other The lathe or slicer will need to be in very times. good condition and set up and operated with

76 Veneer Thickness Tolerance when the pressure bar is contacting the wood, (in.) (mm) (in.) (mm) the knife carriage and the wood work piece are 1/4 (0.250) 6.3 ±0.00 ±0.127 forced apart. To minimize the production of % ( .125) 3.2 ±.004 ±.102 Vv, ( .062) 1.6 ±.003 ±.076 thin veneer at the start of cutting, the lathe %:> ( .031) .8 ±.002 ±.051 should have tight-fitting parts; the pressure bar Mi4 ( .016) .4 ±.001 ±.025 should be closed from the start of cutting and throughout the cutting; and moderate nosebar care to produce veneer that will consistently pressure should be used. This is discussed in meet these specifications. Many commercial more detail by Lutz, Mergen, and Panzer (44). operations run with tolerances approximately Another cause of variable veneer thickness double those listed. is an improper setting of the knife angle or knife pitch. If the pitch is too low, the veneer is thick and thin in waves, the crest of which may Control of Thickness of Veneer Cut on Lathe be 1 or more feet apart. Feihl and Godin {16) The most common fault in veneer thickness is report, "This defect is particularly pronounced thin veneer for the first few revolutions of in winter when veneer is cut from logs that are veneer cut on the lathe. The major cause of this not adequately heated and contain some frozen thin veneer is looseness in the moving parts of wood. When such logs are peeled with a low the lathe. A secondary cause is deflection of the knife angle, the frozen parts tend to produce wood by the pressure bar beyond the knife edge thin veneer and the thawed parts thick veneer." (29). Further, when the knife alone is contact- The corrective measures are to heat the logs to ing the wood, the knife carriage and the wood a uniform temperature and to change to a work piece are pulled together. In contrast, higher knife angle (greater clearance angle),

M 139 941 Figure 27.—An air-operated device for measuring veneer thickness. The pressure on the anvils can be easily changed to suit the species and thickness being measured.

77 A number of investigators (4) have found of one of the feed screws of the lathe carriage that wood having high moisture content is more until the knife frame is parallel to the axis of susceptible than drier wood to being cut thinner the spindles (15). than the knife feed. An example is the tendency Misalinement of the knife and bar may cause of Douglas-fir sapwood veneer to be thinner barrel-shaped bolts and veneer that is thicker than heartwood veneer when cut with the same at the edges than in the middle. This may be lathe settings. One solution is to use less nose- caused by closing of the bar lead and gap at the bar pressure when cutting sapwood of conifers center of the lathe due to heat expansion when than when cutting heartwood. cutting hot bolts. It can best be corrected by Wood having high moisture content, such as heating the knife and bar prior to setting up southern pine sapwood, tends to be thinner than the lathe. Alternately, the lathe can be equipped would be expected from the knife feed when with a cooling system or the nosebar frame may cut at fast speed and with high nosebar pres- have a yoke and pull screw. sure (ÍS), Slower cutting speed or less nosebar A barrel-shaped bolt may also be caused by pressure should result in better thickness bending of the bolt in the lathe. This is most control. likely to occur when cutting long bolts to a Shake, heart checks, or splits in the log, and small diameter. Use of a backup roll can pre- soft centers that allow the bolt to move in the vent bending of the bolt during peeling. chucks can cause irregular veneer thickness. These unwanted thickness variations are re- Control of Thickness of Veneer Cut on the Sheer lated to specific bolts and do not occur on sound The pressure bar is generally bolted into posi- bolts. Larger chucks and continuous end pres- tion on the slicer and the flitch is backed up sure help when cutting bolts with soft centers with a steel table. Consequently, the veneer cut or with large end splits. on the slicer may be more uniform in thickness Misalinement of the pressure bar and knife than veneer cut on the lathe. Since most veneer may cause a thickness variation from one end to cut on a slicer is Míj-inch (1.6 mm) or thinner, the other end of the veneer sheet. If the bar this also makes thickness control less of a prob- moves back at one end of the lathe, the gap or lem than with thicker rotary-cut veneer. horizontal opening is wedge-shaped. As a result, Even so, the first few sheets cut on a slicer the emerging sheet of veneer is thick and short may be thinner than nominal thickness. The at the edge cut with the large gap, and thin and cause is primarily play in the feed mechanism long at the edge cut at the smaller gap. The and the flitch table. As with the lathe, it may veneer coming from the lathe runs in the direc- also be due to compression of the wood beyond tion of the thicker veneer and the bolt takes a the knife edge by the pressure bar (29). A conical shape. The corrective measure is to aline warped flitch that is not held securely against the bar parallel to the knife. Then check for the flitch table by the dogs may also result in play in the nosebar assembly. Movement of the thin veneer. Having all slicer parts closefitting, pressure bar during cutting may be greater at the flitch securely held against the flitch table, one end than the other and so cause misaline- and using moderate nosebar pressure should ment (16). minimize these sources of nonuniform sliced Misalinement of the lead of the pressure bar veneer. with respect to the knife may also cause this Less common reasons for nonuniform veneer phenomenon but it is less likely to occur and include heat distortion of the knife and pressure relatively less important than misalinement of bar that results in veneer cut from near the the gap. center of the slicer to be thin. Heating the knife A conical-shaped bolt may also be caused by a and pressure bar prior to setting up the slicer much larger overhang of one spindle than the is the best way to overcome this problem. Yokes other. The remedy is to center the bolt endwise and pull screws on the pressure bar holder can with respect to the knife. also be used to help correct the alinement of the Similarly, if the knife edge is not parallel to pressure bar to the knife edge. A nonuniformly the axis of the spindle, a conical bolt will be heated flitch may also result in nonuniform generated. The correction is to adjust the nut veneer thickness.

78 M 141 666 Figure 28.—An instrument for measuring roughness of wood surfaces by moving a stylus across the rough sur- face. The insert shows the type of trace the instrument records.

A slicer that indexes the previously cut sur- veneer can cause gluing problems, require ex- face against a stop plate may produce uneven cessive sanding, and cause ñnishing problems. veneer if splinters or other debris come between Measuring the roughness of wood surfaces is the flitch and the stop plate. a complex problem. Peters and Mergen (5^) Slicers having a pawl and ratchet feed must described a stylus trace method they developed have the same number of teeth advanced every for measuring wood surfaces (fig. 28). Earlier stroke. If the mechanism is not set carefully, Lutz (38) described a light-sectioning method an incorrect thickness may be produced. Simi- for measuring roughness of rotary-cut veneer larly, if the feed index train is not braked, (fig. 29). Northcott and Walser (50) have pub- momentum may carry the knife carriage beyond lished a visual veneer roughness scale which in the desired index. turn was obtained by measuring depressions on Splits or shake in flitches can cause uneven the surface of the veneer samples with a dial veneer thickness. These thickness variations do micrometer. For research, the stylus trace not occur with sound flitches. method, the light-sectioning method, and the dial micrometer give values for comparative Control of Veneer Roughness purposes. For mill use, a visual veneer rough- Like nonuniform veneer thickness, veneer ness scale is probably more useful. Actual roughness is undesirable for all end uses. Rough veneer samples that have been measured for

79 surface roughness in the laboratory could be bolt to minimize cutting against the grain (39). kept near the lathe or slicer for visual com- Probably the best control is to adjust the nose- parison with the veneer being produced. bar to increase the pressure just ahead of the The orientation of the wood structure (39) knife tip and so reduce splitting ahead of the and the growth rate of softwood trees (iO) knife. Proper heating of the wood and use of a affect the smoothness of knife-cut veneers. sharp knife also help reduce this roughness. When cutting against the grain of the wood Another type of roughness is a fuzzy surface. fibers, annual rings, or wood rays, the wood It is most common on low-density hardwoods tends to split ahead of the knife and into the like cottonwood that contain tension wood. Over- wood work piece, causing depressions on the heating of any species may also cause fuzzy sur- tight side of the veneer. The annual ring effect faces. Control may include log selection to avoid is most pronounced when rotary-cutting fast- tension wood, cutting the wood at as low a tem- grown softwoods at small core diameters. The perature as is practical, and keeping the knife ray effect is pronounced when quarter-slicing sharp. An extra hard knife will keep a sharp goes beyond the true quarter. Cutting against edge longer than a soft knife and can be used the fibers occurs around knots, with curly grain with low-density woods. Use of a slightly eased and with interlocked grain. The thicker the fixed nosebar edge and continuous flushing of veneer, the more likely the veneer will be rough. the surface between the wood and the nosebar It is sometimes possible to mount the flitch or with cold water may also help.

M 141 667 Figure 29.—An instrument for measuring veneer surfaces by light sectioning. The insert shows what is seen through the magnifying glass of the instrument.

80 Shelling or separation of the springwood Corrugated veneer with three or four waves from the summerwood may occur when rotary- per inch of veneer is generally associated with cutting or flat-slicing both softwoods and hard- too high a knife angle. Feihl and Godin (16) woods that have a relatively weak zone between report corrugated veneer can also be caused by the springwood and summerwood. Hemlock, cold or dry wood and by setting the knife edge true firs, western redcedar, and angelique are too low. Other causes are too much overhang on species that may develop shelling. Overheating the spindles, cutting to a small core without of the wood, too much nosebar pressure, too adequate support for the core, and wood bolts sharp a nosebar, or a dull knife may contribute that become loose in the chucks. Corrective to shelling. measures are obvious from the stated causes. Shattering of the veneer surface is somewhat like shelling and may occur with wood having a Control of Cracks or Breaks into high moisture content and low permeability. the Veneer For example, Douglas-fir sapwood and sinker Breaks into the veneer may be on the side of redwood bolts may develop shattered veneer the veneer that is next to the knife or on the surfaces if cut at high speed and with high side next to the pressure bar during cutting. By nosebar pressure. Apparently water in the wood far the most common are small cracks that de- is compressed so fast that it ruptures the wood velop on the side of the veneer next to the knife. structure to escape. Lower nosebar pressure They may be caused by splitting ahead of the and slower cutting speed reduce the occurrence knife edge or by bending the veneer as it passes of shattered veneer surfaces. the knife after it is cut. The terms tight and Nicks on the knife edge or pressure-bar edge loose side of the veneer refer to this phenom- may cause scratches on the veneer. Scratches enon, with the loose side being the side that has from the knife occur on both the tight and loose the checks. These small breaks are also known side of the veneer while scratches from the pres- as knife checks, lathe checks, or slicer checks. sure bar occur only on the tight side of the Less prevalent but perhaps more serious are veneer. These scratch marks are so common breaks on the bar side or tight side of the that they can often be used to distinguish one- veneer. Three samples are grain separation, half-round from flat-sliced veneer. The scratches lifted grain, and cracks approximately perpen- on the half-round veneer are at a right angle to dicular to the veneer surface. the length of the sheet while those on flat-sliced Loosely cut veneer is weak in tension perpen- veneer are at some acute angle corresponding dicular to the grain. As a result, it may develop to the draw of the slicer. Careful examination splits or break readily during handling, thus of the veneer, followed by honing the knife and lowering the grade of the veneer. Deep checks pressure bar when necessary, will minimize in face veneer may also contribute to surface these scratch marks. This is particularly im- checks in furniture or other finished panels. On portant for decorative face veneer. The scratches the other hand, loosely cut veneer may develop may take more stain than surrounding wood more wood failure than tightly cut veneer. As a even if the sanded wood appears to be free of result, veneer is sometimes cut loosely on pur- scratches. pose to increase the wood failure when the Grain raising is occasionally seen on soft- plywood is evaluated by the standard plywood wood veneer cut from wood having a dense shear test. summerwood and much less dense springwood. Three methods have been used to measure Excessive pressure from the nosebar overcom- looseness of veneer. One method is to pull presses the springwood. After the veneer is cut, 1-inch- (2.54 cm) long veneer samples apart in the springwood recovers, resulting in raised tension perpendicular to the grain on a suitable grain. The corrective measure is to reduce the test machine (fig. 30). Because of variability, nosebar pressure. Feihl and Godin (16) report a minimum of about 30 samples should be tested that bulging of knots in the core is related to to obtain a value for a given cutting condition. raised grain and they suggest increasing the The values obtained can be compared with knife angle as well as decreasing the nosebar values for matched sawn and planed pieces of pressure as means of correcting this fault. the same size.

81 A second method of evaluating veneer checks Assuming proper heating schedules are being is to apply an alcohol-soluble dye to the checks used as described earlier, the temperature by brushing it on the dry veneer surfaces or by through the flitch or bolts should be relatively dipping the end of the dry veneer in the dye. uniform. One way to check the bolt temperature The dye penetrates into the checks. The depth is to drill a %-inch- (6.3 mm diameter hole of checks as a percentage of the veneer thick- radially an inch or two (2.5 to 5 cm) deep at ness can be estimated from scarfed sections of the center of the cores remaining after cutting the samples (fig. 31). The method works very veneer from large- and small-diameter bolts. well with relatively impermeable veneer such as A thermometer should immediately be inserted Douglas-fir heartwood where the dye is gen- in the hole and the temperature recorded. This erally confined to the checks; it is less satisfac- temperature should be within 10° F (5° C) of tory with permeable veneer such as southern the desired temperature for good cutting. This pine sapwood due to overall penetration of the method is recommended over measuring the dye into the wood. temperature at the surface of the bolt, as the A third method is to flex the veneer across surface temperature of a heated block changes the grain. Tightly cut veneer is suffer than very fast when it is exposed to air. loosely cut veneer. If the measured temperature is not satisfac- Two factors are most important in minimiz- tory, the heating schedules should be rechecked ing depth of checks on the loose side of the and the actual temperatures in various posi- veneer. They are adequate heating of the wood tions in the heating vat should be monitored and use of adequate nosebar pressure. Factors with thermocouples throughout the heating that may increase checking are logs that have cycle. partially dried and use of a knife bevel much Nosebar pressure was described in detail greater than is commonly used. earlier. For quality control, perhaps the most useful procedure is to be certain that the lathe or slicer settings are made with instruments, and that gages are mounted on the equipment to show any unwanted movement of the nosebar with respect to the knife edge during cutting. With good veneer species like yellow birch / and yellow-poplar, it is possible to cut veneer ^1 as thick as Vs-inch (3.2 mm) with no visible <] checks on the knife side of the veneer. Grain separation is similar to shelling and is a failure of wood between annual rings. The defect may not be noticed in the green veneer but later causes trouble when the plywood made from the veneer is bent as for a boat hull. Two species that have developed the defect are okoume and lauan. The cause is related to rela- tively weak zones in the wood and is generally considered to be due to setting the bar with too much lead and too small a gap. If suspected, it ■■a § may be detected in dry veneer or plywood by tapping with a coin or stroking with a stiff \ brush. The void causes a different noise than the noise that comes when tapping or brushing sound veneer. V V Lifted grain is a separation of large groups M 108 074 of fibers in figured veneer like curly birch (16). Figure 30.- -A veneer specimen in the grips of a ten- sion testing machine. It is serious because such areas cannot be

82 M 107 770 Figure 31.—A scarfed sample of birch veneer to show checks about one-third of the thickness of the veneer. A dye was applied prior to scarfing to make the checks stand out.

sanded to a smooth surface. Careful setting of surfaces and recording the spacing. Commonly, the knife and pressure bar may minimize this buckle is rated visually as mild, moderate, or defect in thin face veneer such as %4-inch severe. (1 mm). Extreme curly grain should not be Buckle in green veneer may be caused by re- cut into thicker veneer if lifted grain is to be action wood or by uneven pressure against the avoided. bolt or flitch during cutting. The last type of cracks to be discussed in- Compression wood in softwoods and tension volves breaks perpendicular to the tight side. wood in hardwoods have different longitudinal They may occur if excessive nosebar pressure stresses than normal wood. When sheets of is used, or if the nosebar lead puts excessive veneer containing both reaction wood and restraint on the veneer as it passes between the normal wood are cut, the veneer may buckle knife and the pressure bar. Breaks on the tight as it comes from the lathe or sheer. Drying side of the veneer can be detected by the ten- accentuates this buckle. Logs from species sion test and by the alcohol-soluble dye test the known to be prone to develop reaction wood same as breaks into the loose side of the veneer. should be examined prior to cutting and not Careful setting of the pressure bar will elimi- be cut into veneer if the reaction wood is pro- nate this problem. nounced. Uneven pressure against the bolt or flitch Control of Buckle in Green Veneer may be due to heat distortion of the knife and Buckle is undesirable as it interferes with pressure bar setting on the lathe or slicer ; bow- edge gluing, glue spreading, and panel layup. ing of small-diameter bolts on the lathe; jam- When it is severe it may cause overlaps or ming of a chip or splinter between the pressure splits in the plywood. Buckled veneer caused bar and the bolt or flitch; or a tight spot due by reaction wood may also cause warped panels to a local deviation of the knife or pressure in service. bar edges from a straight line. Buckle, like end waviness, may be measured As discussed earlier, heat distortion can be by deviation from a plane surface by placing minimized by heating the knife and pressure the buckled veneer between two flat parallel bar prior to setting them. Bowing of the bolt

83 may be minimized by reducing the nosebar neer as it comes from the dryer. This is true pressure and by using a backup roll. Some lathe of a dryer having longitudinal circulation, cross operators judge the correct nosebar pressure by circulation, or jet impingement circulation. It is whether the veneer buckles in the center of the similarly true for a progressive platen-type sheet. If the center of the veneer ribbon is dryer. buckled, the pressure is too high and the nose- For example, veneer dried to an average bar gap is widened. moisture content of 8 percent will generally A splinter or chip jammed between the knife have a range of moisture content from about and bar in effect puts very high local pressure 2 to 20 percent. This is because the equilibrium on the wood and causes the veneer to be thin. moisture conditions in the dryer are for all A bump builds on the bolt or flitch. If it is practical purposes 2 percent or less. When pronounced, the veneer may develop a hole at drying to an average moisture content of 8 per- this area and the knife may be bent. The cor- cent, the faster drying veneer may come to 2 rection is to stop cutting, open the pressure bar, percent and the slower drying to 20 percent remove the chip or splinter, close the bar, and moisture content. In other words, any differ- resume cutting. Use of a roller bar helps reduce ence in the drying rates of different areas of this defect as the chips are more readily pushed the same sheet of veneer then results in a wide past the opening between the knife and pressure range in final moisture content in the veneer bar. Setting a fixed bar with more lead may as it comes from the dryer. help reduce this problem. Having the bolt or To keep this problem to a minimum, the flitches clear of bark and loose splinters is good green veneer should be sorted for thickness, practice and will reduce jamming of particles moisture content, and density. Better control between the surface of the bolt or flitch and will probably result if the green veneer is also the pressure bar. sorted for sapwood and heartwood and by Finally, if the knife and pressure bar are not species. Assuming the veneer is being sorted ground straight, there may be a local tight spot as well as possible to have veneer of one type that will result in buckled veneer. The correc- being dried at a time, the next point to check tion is to grind the knife and bar straight. is the uniformity of drying conditions in dif- Both surfaces of the knife edge should be ex- ferent parts of the dryer. amined and if necessary both should be ground Modern veneer dryers are generally designed to straighten the edge (2i). to have uniform temperature and air movement throughout the dryer. However, it may be Dry Veneer worthwhile to check these factors. Is the tem- Most veneer readily dries satisfactorily for perature at the top conveyor the same as it is the intended end use. But since veneer is easy at the bottom conveyor? Is the air speed ap- to dry, potential problems are sometimes over- proximately the same in all parts of the dryer? looked. One method of checking this is to run matched Some veneer drying problems are nonuni- samples of veneer through different portions form moisture content in the veneer as it of the dryer. For example, one sample can be emerges from the dryer, buckle and end wavi- run through the left side of the upper conveyor, ness of veneer sheets, splits and checks in the another through the right side of the upper veneer, a veneer surface that is difficult to glue, conveyor, another through the left side of a scorched veneer surfaces, veneer that shows lower conveyor, and so on. Then carefully check signs of collapse, honeycomb, or casehardening, these samples for moisture content immediately excessive veneer shrinkage, and undesirable out of the dryer. If this test shows that one color. portion of the dryer is consistently drying ve- neer faster than another, drying rates can Control of Final Moisture Content sometimes be equalized by adding steam coils, Probably the most universal problem in dry- baffles, or fans where needed in the dryer. ing veneer in a progressive mechanical veneer- Another way of controlling the final mois- type dryer operating above 220° F (104° C) ture content is to dry all of the veneer to 5 per- is the nonuniform moisture content in the ve- cent moisture content or less. This may result

84 in overdrying of some of the veneer, but it will In most cases, buckling can be minimized by result in a narrower range of veneer moisture. redrying in a plate dryer. The redrying tem- A very common method of reducing the perature and time will depend on the moisture spread of moisture in the veneer is to electron- content of the veneer (4^1), ically measure the moisture content in each piece of veneer as it comes from the dryer. Control of Splits Veneer that has a moisture content higher than the desired maximum is marked and pulled Splits in veneer that has been dried in a pro- separately for further drying. Leaving this wet gressive mechanical dryer are generally related veneer in a solid stack overnight will help to to splits that were in the green veneer or result equalize the moisture content. A re-sort through from rough handling. If stacks of green veneer the moisture detector the next day will reduce must be held before drying, the ends should be the number of pieces that need to be redried. protected from end drying by covering them Some moisture meters are sensitive to wood with a plastic sheet (such as polyethylene) or temperature as well as moisture content. They if necessary by spraying them with water. should be calibrated under the conditions in A recent development for controlling han- which they will be used. dling splits is green veneer taping. Tape is Another method that is sometimes used when applied at the lathe primarily to veneer thinner nonuniform moisture content is a serious prob- than 1/26 inch (1 mm). Taping reportedly im- lem is to dry in two stages. In the first pass, proves the veneer grade, and reduces the need the veneer is brought to an average moisture to splice and repair veneer. Forest Products content of about 20 percent. It is then stacked Laboratory experiments showed that i/2-inch- overnight to allow some equalization and rerun (12.7 mm) wide flexible tape applied to the the next day to the average moisture content spurred ends of the green veneer reduces end desired. waviness. High-frequency or microwave units have been Another method of reducing handling splits used experimentally at the dry end of the dryer is to dry rotary-cut veneer in a continuous rib- to equalize the moisture content of the veneer. bon using a wire-mesh conveyor in a mechan- Both these methods work on the principle that ical dryer. The method was used as early as the higher moisture areas in the veneer absorb 1950 with birch veneer which was reeled as more energy. Heating and drying are propor- it came from the lathe and then unreeled into tional to this absorption of energy. Both of the dryer. The dryer veneer was then clipped these methods do equalize moisture content in for grade. the veneer, but they have not been generally More recently a system has been developed adopted because of cost (59). where softwood veneer is stored on long trays It is possible to dry veneer to controlled mois- and then fed in line to the dryer. In addition ture contents in superheated steam at atmos- to reducing splits, recovery is reportedly im- pheric pressure. To date this method has not proved because the veneer is clipped dry and it been used commercially. is not necessary to oversize to compensate for variability in shrinkage. Control of Buckle Buckle in veneer may be caused by stresses Control of Veneer Surfaces for Gluability in the wood, by reaction wood, by irregular Poor glue bonds have been reported with grain with resulting irregular drying rates and veneer dried in direct oil-fired dryers operating irregular grain with resulting shrinkage, and at temperatures as high as 550° F (288° C). possibly also by improper setting of the lathe This is less of a problem with direct gas-fired or sheer. Use of the maximum restraint that dryers and less yet with steam-heated dryers. will hold the veneer flat without causing it to Dropping the temperature to 400° F (208° C) split due to shrinkage stresses will help to or lower improved the gluability of the veneer. minimize buckle. Similarly, anything that can Causes of glue interference may be weakening be done to dry the veneer to as uniform a mois- of the surfaces and extractives brought to the ture content as possible will reduce buckling. wood surface during high-temperature drying.

85 At any rate, use of a lower drying temperature early stages of the drying. Sweetgum dried at and prevention of overdrying the veneer are 350° F (177° C) had much more honeycomb the common means of overcoming veneer glu- than sweetgum heartwood dried at 150° F (66° ing problems. C). Experiments at Madison showed that Vs- inch (3.2 mm) overcup oak dried at 320° F Control of Dryer Fires and (160° C) might shrink as much as 20 percent Scorched Veneer in thickness. The solution to these drying prob- lems in all cases appears to be to use a lower High drying temperatures may cause drying temperature. scorched veneer and possibly fires in the dryer. Casehardening was at a maximum in Vs-inch At temperatures from 200° to 300° F (93° to (3.2 mm) heartwood of sweetgum when dried 149° C), extraneous materials volatilize from at temperatures of 120° to 160° F (49° to 71° wood. From 300° to 400° F (149° to 204° C), C). Casehardening can be removed by use of there is scorching and slow evolution of ñam- high temperature, particularly if the veneer mable gases from the wood. This progressively has a high moisture content. becomes more rapid until at about 600° to 650° (316° to 346° C) the wood can ignite spontane- Control of Shrinkage ously. Widthwise shrinkage of flat-grain veneer Even if wood does not ignite spontaneously generally decreases with increasing drying until the temperature at its surface reaches temperature. For example, Vs-inch (3.2 mm) about 650° F (346° C), if the surface becomes yellow-poplar dried at 150° F (66° C) shrank charred, charcoal gases may ignite at a temper- 6 percent; when dried at 250° F (121° C) it ature as low as 450° F (232° C). Extraneous shrank bVi percent; and when dried at 350° materials such as turpentine also ignite at a F (177° C) it shrank 4^2 percent. In contrast, temperature of about 450° F (232° C). the shrinkage in thickness tends to increase Veneer being dried in dryers operating at with an increase in drying temperature. 400° F (204° C) or less sometimes ignites in the dryer. These fires may be caused by a static Control of Color spark that ignites flammable gases of volatile extraneous materials. Color in face veneer can often be controlled Avoiding overdrying and use of controlled to some degree by varying the time that the lower drying temperatures are the primary green veneer is held in a stack prior to drying. means of preventing dryer fires and scorched In general, the wet veneer tends to oxidize and veneer. darken in storage. Consequently, if a light color is desired, as with the sapwood of hard maple, the veneer should be dried as quickly as possible Control of Collapse^ Honeycomb^ and after cutting. In other cases, it may be desirable Casehardening to have some color change take place in the Collapse and honeycomb may occur in species green veneer stack. An example is black walnut. that are relatively nonporous. Typical examples The color of the sapwood and heartwood would be Vs-inch (3.2 mm) and thicker heart- changes gradually in the warm green stack. wood of sweetgum and overcup oak. Collapse When the desired color is reached, the veneer is in sweetgum heartwood is likely to occur in sent through the veneer dryer.

86 VENEER YIELDS AND VOLUME NEEDED FOR A PLANT VENEER YIELDS (ROTARY CUTTING) With knife-cut veneer one might assume that neer. Some techniques described include backup veneer recovery could equal the volume of the rolls and retractable chucks to aid cutting to log minus the volume of the core. Unfortunately smaller cores, use of a moving knife to separate this is not the typical case. For example, during the veneer ribbon going to different trays, peeling of Douglas-fir in commercial plants, veneer clippers having devices to sense open Woodfin (68) found losses due to: spurring, 2 defects and clip automatically for maximum percent; roundup, 5V2 percent; green end clip- yield, and veneer sheet composers. per loss, 22 percent; below-grade veneer, 6 per- A technique for increasing yield that has cent; core, 91/2 percent; and veneer shrinkage been described (23) but not adapted is to pre- 3 percent. Thus the actual recovery of dry ve- cisely measure block diameters, feed the in- neer was only 52 percent of the total green formation to a computer which in turn directs block cubic volume. This is typical of yield the charging device to precisely chuck the block studies in industrial plants. in the geometric center. Estimated increased The losses at different stages vary with the yields are up to 7 to 8 percent. quality and diameter of veneer blocks. Cylin- drical logs have less loss from roundup than Drying veneer in a ribbon and clipping after logs with pronounced taper or crook. Assuming drying has been reported to increase yields as the core diameter is constant, large-diameter much as 4 percent. However, extra energy is logs have a smaller percentage loss as core than used to dry some veneer that is then clipped out small-diameter logs. and not used to make plywood. Sharp increases in log costs in 1973 stim- If all conditions are favorable, it is possible ulated interest in means of improving veneer to obtain high veneer recovery in a commercial yields. Baldwin's book, *Tlywood Manufactur- plant. For example, Knutson (34) reported 87 ing Practices'' (2), describes good industry percent yield of Vio-inch Douglas-fir from sound practice in 1975 to maximize recovery of ve- logs 20 to 23 inches in diameter.

VENEER YIELDS (SLICED) In general veneer recovery is highest by ro- Some commercial slicing operators have re- tary cutting, less by flat-slicing, and least by ported that, for logs 15 inches and larger in quarter-slicing. Yields are less for slicing be- diameter, the yield of flat-sliced veneer is about cause of losses when sawing the flitches and equal in equivalent thicknesses to the board foot when clipping straight edges on the relatively value by the Scribner Decimal C log rule. narrow sliced veneer.

87 VOLUME OF TIMBER NEEDED TO SET UP A VENEER PLANT A typical plant in the United States making ety of species. Typical plants are small and use construction and industrial plywood uses ap- less volume of logs than plywood plants. The proximately 40 million board feet of logs per end-product is generally an expendable low-cost year. The smallest economically suitable con- container. Cheap stumpage is essential. Lower struction plywood plant uses about 15 million quality logs than those acceptable for plywood board feet of logs a year. If the volume of wood panels are successfully used for container available at a site is less than this, there is little veneer. point in considering it for structural plywood. Two examples of the importance of available Hardwood and decorative plywood plants are timber are the development of southern pine generally smaller than structural plywood softwood plywood and hickory- or pecan-faced plants. In addition, they frequently use a hardwood plywood during the 1960's. Both of variety of species. Therefore, while 12 to 15 these groups of species are relatively difficult to million board feet of logs may be used in a year, process into veneer and plywood. Yet, because a hardwood species that could be supplied at the of the large available timber supply of each, rate of 5 million board feet a year could prob- they became realities. Southern pine is challeng- ably be used satisfactorily. ing the western softwood plywood industry, and An even greater diversity of species is cut by hickory and pecan are a major group used for mills making face veneers. Manufacturers of decorative face veneer. face veneers state that it is imperative that a In some mixed forests of the tropics, the total continuing supply of a new face veneer must be stumpage is large, but no one species occurs in available. Otherwise the cost of advertising and large volume. In these areas it is often difficult other promotion needed to get a new species to exploit new species for veneer. This is true accepted is not warranted. even for a species that has good technical prop- Core and crossband veneer is generally not erties for use as veneer. specified by the ultimate customer. Hence, in- The cost of developing information on a new troducing a new species is not as difficult as species, determining how it should be handled with face veneers. The technical properties of in production, introducing it, and promoting it the wood and the volume availability at a rea- in a product line is very costly. If a species is sonable cost are important for core and cross- available only on a sporadic basis, it is gener- band veneers. ally not economical for a manufacturer to uti- Container veneer often is made from a vari- lize the species. LITERATURE CITED

1. American Plywood Association 20. Fleischer, H. O. 1973. How to control veneer dryer emissions. 1959. Heating rates for logs, bolts, and flitches APA sem., reprinted in Wood and Wood Prod. to be cut into veneer. U.S. For. Prod. Lab. Nov. 1973, p. 94 B,C,D. Rep. No. 2149. 2. Baldwin, Richard F. 21. Fondronnier, J., and J. Guillerm 1975. Plywood manufacturing practices. Miller 1967. Guide pratique de la dérouleuse (Fr.). Freeman Pub., Inc. San Francisco, p. 260. Cent. Tech. du Bois, 10 Ave. de St. Mande, 3. Bethel, James S., and Robert J. Hader Paris 12e, Fr. 1952. Hardwood veneer drying. J. For. Prod. 22. Fondronnier, J., and J. Guillerm Res. Soc. 2(5):205-215. 1975. Le Flambage du bois lors de son déroulage. 4. Bryant, B., T. Peters, and G. Hoerber Cent. Tech, du Bois, 10 Ave. de St. Mande, 1965. Veneer thickness variation: its measure- Paris 12e, Fr. ment and significance in plywood manufacture. 23. Foschi, R. 0. For. Prod. J. 15(6) :233-237. 1976. Log centering errors and veneer yield. 5. Burrell, J. F. For. Prod. J. 26(2) :52-56. Feb. 1973. Plywood plants of the future. Plywood 24. Godin, V. and Panel Mag. 14(6) :28-30. Nov. 1968. The grinding of veneer knives. Gan. Dep. 6. Cade, J. C, and E. T. Choong For., For. Prod. Res. Br., Pub. No. 1236. 1969. Influence of cutting velocity and log diam- eter on tensile strength of veneer across the 25. Grantham, John and George Atherton grain. For. Prod. J. 19(7) :52-53. 1959. Heating Douglas-fir blocks—does it pay? 7. Collett, B. M., A. Brackley, and J. D. Gumming Greg. For. Prod. Res. Center. Bull. No. 9. 1971. Simplified, highly accurate method of pro- 26. Hancock, W. V., and H. Hailey ducing high-quality veneer. For. Ind. 98(1): 1975. Lathe operators^ manual VP-X-130. Can. 62-65. West. For. Prod. Lab., Vancouver, B.C. Jan. 8. Gomstock, G. L. 27. Harrar, E. S. 1971. The kinetics of veneer jet drying. For. 1954. Defects in hardwood veneer logs: their Prod. J. 21(9):104-111. frequency and importance. USDA For. Serv. 9. Dokken, H. M., and V. Godin Southeast. For. Exp. Stn. Pap. No. 39. Ashe- 1975. Instrument for measuring knife pitch ville, N.C. angle on veneer lathes. For. Prod. J. 25(6): 28. Hillis, W. E. 44-45. June. 1962. Wood extractives. Academic Press, N.Y. 10. Feihl, A. 0. 513 p. 1959. Improved profiles for veneer knives. Gan. 29. Hoadley, R. B. Woodworker. Aug. 1962. Dynamic equilibrium in veneer cutting. 11. Feihl, A. 0. For. Prod. J. 12(3) : 116-123. 1972. Heating frozen and nonfrozen veneer logs. 30. Hann, R. A., R. W. Jokerst., R. S. Kurtenacker, For. Prod. J. 22(10) :41-50. C. C. Peters, and J. L. Tschernitz. 12. Feihl, A. 0., and M. N. Garroll 1971. Rapid production of pallet deckboards 1969. Rotary cutting veneer with a floating bar. from low-grade logs. USDA For. Ser. Res. For. Prod. J. 19(10) :28-32. Pap. 154. For. Prod. Lab., Madison, Wis. 13. Feihl, A. 0., H. G. M. Golbeck, and V. Godin 31. Kivimaa, E. 1965. The rotary cutting of Douglas-fir. Gan. 1952. Was ist die Abstumpfung der Holzbear- Dep. For., For. Prod. Res. Br., Pub. No. 1004. beitungswerkzeuge? Holz als Roh- und Werkst. 14. Feihl, A. O., and V. Godin 10:425-428. 1967. Wear, play, and heat distortion in veneer 32. Kivimaa, E., and M. Kovanen lathes. Gan. Dep. For., For. Prod. Res. Br., 1953. Microsharpening of veneer lathe knives. Pub. No. 1188. State Institute for Tech. Res., Helsinki, Fini., 15. Feihl, A. 0, and V Godin Rep. No. 126, 24p. 1970. Setting veneer lathes with aid of instru- 33. Knospe, Lothar ments. Gan. Dep. For., For. Prod. Res. Br., 1964. The influence of the cutting process in Pub. No. 1206. slicing and peeling on the quality of veneers. 16. Feihl, A. 0., and V. Godin Holztechnologie (Wood Tech.) 5(1):8-14. (in 1970. Peeling defects in veneer, their causes Ger.) and control. Gan. Dep. For., For. Prod. Res. 34. Knudson, R. M., R. W. G. Scharpff, R. J. Mastin, Br., Tech. Note 25. and D. Barnes 17. Fleischer, H. 0. 1975. Effect of lathe settings on veneer yield. 1949. Experiments in rotary veneer cutting. J. For. Prod. J. 25(10) :52-56. For. Prod. Res. Soc. 3:137-155. 35. Kubinsky, Eugen and Milan Sochor 18. Fleischer, H. 0. 1968. New softening treatment for beech logs 1953. Veneer drying rates and factors affect- before rotary peeling to veneers. For. Prod. ing them. J. For. Prod. Res. Soc. 3(3):27-32. J. 18(3): 19-21. 19. Fleischer, H. O. 36. Kubier, Hans 1956. Instruments of alining the knife and nose- 1959. Studies of growth stresses in trees. Holz bar on the veneer lathe and slicer. For. Prod. als Roh- und Werkst. 17(1) :l-9; 17(2) :44-54; J. 6(l):l-5. and 17(3) :77-86.

89 37. Lockard, C. R., J. A. Putnam, and R. D. Carpenter 53. Palka, L. C. 1963. Grade defects in hardwood timber and 1974. Veneer cutting review. VP-X-135. Can. logs. USDA Agrie. Handb. 244. West. For. Prod. Lab., Vancouver, Canada. 38. Lutz, John F. 54. Peters, C. C, and A. Mergen 1952. Measuring roughness of rotary-cut veneer. 1971. Measuring wood surface smoothness: a The Timberman 53(5) :97,98,100. proposed method. For. Prod. J. 21(7) :28-30. 39. Lutz, John F. 55. Pillow, Maxon Y. 1956. Effect of wood-structure orientation on 1943. Compression wood: importance and detec- smoothness of knife-cut veneers. For. Prod. J. tion in aircraft veneer and plywood. U.S. For. 6(ll):464-468. Prod. Lab. Rep. No. 1586. Madison, Wis. 40. Lutz, John F. 56. Pillow, Maxon Y. 1964. How growth rate aifects properties of 1955. Detection of figured wood in standing softwood veneer. For. Prod. J. 14(3) :97-102. trees. U.S. For. Prod. Lab. Rep. No. 2034. 41. Lutz, John F. Madison, Wis. 1970. Buckle in veneer. USDA For. Serv. Res. 57. Pillow, Maxon Y. Note FPL^0207. For. Prod. Lab., Madison, 1962. Effects of tension wood in hardwood lum- Wis. ber and veneer. U.S. For. Prod. Lab. Rep. No. 42. Lutz, John F. 1943. Madison, Wis. 1972. Veneer species that grow in the United 58. Puget Sound Log Scaling and Grading Bureau States. USDA For. Serv. Res. Pap. FPL 167. Columbia River Log Scaling and Grading Bureau For. Prod. Lab., Madison, Wis. Grays Harbor Log Scaling and Grading Bureau 43. Lutz, John F., A. Mergen, and H. Panzer Southern Oregon Log Scaling and Grading Bureau 1967. Effect of moisture content and speed of Northern California Log Scaling and Grading cut on quality of rotary-cut veneer. USDA Bureau For. Serv. Res. Note FPL-0176. For. Prod. 1969. Official log scaling and grading rules. Lab., Madison, Wis. Portland, Oreg. 44. Lutz, John F., A. F. Mergen, and H. Panzer 59. Resch, H., C. A. Lofdahl, F. J. Smith, and C. Erb 1969. Control of veneer thickness during rotary 1970. Moisture leveling in veneer by microwaves cutting. For. Prod. J. 19(12) :21-27. and hot air. For. Prod. J. 20(10) :50-58. 45. Lutz, John F., and R. A. Patzer 1966. Effects of horizontal roller-bar openings 60. Scheffer, T. C. on quality of roller-cut southern pine and yel- 1969. Protecting stored logs and pulpwood in low-poplar veneer. For. Prod. J. 16(10) : 15-25. North America. Sonderdruck aus: Mater, und 46. MacLean, J. D. Organismen 4 Heft 3, 167-199. Verlag: Dunc- 1946. Rate of temperature change in short- ker and Humblot, Berl. 41. length round timbers. Trans. Amer. Soc. Mech. 61. Scheffer, T. C, and R. M. Lindgren Eng. 68(1:1): 1-16. 1940. Stains of sapwood and sapwood products 47. McKenzie, W. M., and B. M. McCombe and their control. USDA Tech. Bull. No. 714. 1968. Corrosive wear of veneer knives. For. 62. Seibo, M. L. Prod. J. 18(3):45,46. 1975. Adhesive bonding of wood. U.S. Dep. 48. Meriluoto, Jaakko Agrie, Tech. Bull. No. 1512. 1971. Melting of birch bolts. Paperi ja Puu 63. U.S. Department of Commerce 53(9):493-497. Hardwood and decorative plywood. Prod. Stand. 49. Nearn, W. T. PS 51-71. 1955. Effect of water soluble extractives on the 64. U.S. Department of Commerce volumetric shrinkage and equilibrium moisture Construction and industrial plywood. Prod. Stand. content of eleven tropical and domestic woods. PS 1-74. Bull. 598, Pa. State Univ., Coll. of Agrie, 65. U.S. Forest Products Laboratory, Forest Service Agrie. Exp. Stn., University Park, Pa. 1974. Wood Handbook. U.S. Dept. Agrie, 50. Northcott, P. L., and D. C. Walser Agrie. Handb. No. 72, Rev. 1965. Veneer-roughness scale. B. C. Lumber- 66. U.S. General Services Administration man. July. Boxes, wood, wirebound. Fed. Specif. PPP-B- 51. Northeastern Forest Experiment Station 585b. 1965. A guide to hardwood log grading. USDA For. Serv., Northeast For. Exp. Stn. Handb., 67. Walser, D. C. Rev., Upper Darby, Pa. 1975. Preloading the pressure-bar assembly for 52. Northern Hardwood and Pine Manufacturers improved veneer-lathe setting accuracy. For. Association Prod. J. 25(7) :44-45. July. 1968. Offícial grading rules for northern hard- 68. Woodfin, Richard O., Jr. wood and softwood, logs and tie cuts. Green 1973. Wood losses in plywood production. For. Bay, Wis. Prod. J. 23(9), Sept.

90 APPENDIX I—NOMENCLATURE OF WOOD SPECIES AND VENEER

Accurate identification is the key to efliicient identifies an individual species. Included here utilization of individual wood species. Wood is are the oflflcial common name of a species and made up of a vast number of species, each with the corresponding botanical name. In turn, its own properties, and known by a variety of these wood names are tied to the names for common names. Only the precise name properly veneer.

NOMENCLATURE OF WOOD SPECIES AND VENEER

Commercial name of veneer Official common Botanical name tree name General Specific

UNITED STATES HARDWOODS Alder Nepal alder Nepal alder Alnus nepalensis Red alder Red alder A. rubra American ash Black ash Black ash Fraxinus nigra Oregon ash Oregon ash F. latifolia Pumpkin ash Pumpkin ash F. profunda White ash Blue ash F. quadrangulata Green ash F. pennsylvanica White ash F. americana Shamel ash Shamel ash F. uhdei Aspen Popple Bigtooth aspen Populus grandidentata Quaking aspen P. tremuloides Basswood American basswood Tilia americana White basswood T. heterophylla Beech American beech Fagus grandifolia Birch Yellow birch Betula alleghaniensis Sweet birch B. lenta Paper birch B. papyrifera Alaskan paper birch B. papyrifera var. humilis Gray birch B. populifolia River birch B. nigra Box elder Box elder Acer negundo Buckeye Ohio buckeye Aesculus glabra Yellow buckeye A. octandra Butternut Butternut Juglans cinérea Cherry Black cherry Prunus serótina Cottonwood Balsam poplar Populus balsamifera Black cottonwood P. trichocarpa Eastern cottonwood P. deltoides Swamp cottonwood P. heterophylla Elm Rock elm Cedar elm Ulmus crassifolia Rock elm U. thomasii Winged elm U. alata Soft elm American elm (gray elm) U. americana Slippery elm (red elm) U. rubra Eucalyptus Robusta eucalyptus Eucalyptus robusta Gum Sweetgum Liquidambar styraciflua Hackberry Hackberry Celtis occidentalis Sugarberry C. laevigata Hickory Mockernut hickory Carya tomentosa Pignut hickory C. glabra Shagbark hickory C. ovata Shellbark hickory C. laciniosa Holly American holly Ilex opaca Koa Koa Acacia koa Locust Black locust Robinia pseudoacacia Honeylocust Gleditsia triacanthos Madrone Pacific madrone Arbutus menziesii Magnolia Cucumbertree Magnolia acuminata Southern magnolia M. grandiflora Sweetbay M. virginiana

91 NOMENCLATURE OF WOOD SPECIES AND VENEER—continued

Commercial name of veneer Official common Botanical name —_ trPPLice TinTTTIPIldHlc General Specific

UNITED STATES HARDWOOD—continued Maple Hard maple Black maple Acer nigrum Sugar maple A. saccharum Oregon maple Bigleaf maple A. macrophyllum Soft maple Red maple A. ruhrum Silver maple A. saccharinum Oak Red oak Black oak Quercus velutina California black oak Q. kelloggii Cherrybark oak Q. fálcala var. pagodaefolia Laurel oak Q. laurifolia Northern red oak Q. rubra Nuttall oak Q. nuttallii Pin oak Q. palustris Scarlet oak Q. coccínea Shumard oak Q. shuntardii Southern red oak Q. fálcala Water oak Q. nigra Willow oak Q. phellos White oak Bur oak Q. macrocarpa Chestnut oak Q. prinus Chinkapin oak Q. muehlenhergii Delta post oak Q. stellata var. mississippiensis Durand oak Q. durandii Live oak Q. virginiana Oregon white oak Q. garryana Overcup oak Q. lyrata Post oak Q. stellata Swamp chestnut oak Q. michauxii Swamp white oak Q. bicolor White oak Q. alba Ohia Ohia Metrosideros polymorpha Oregon myrtle California laurel Umbellularia californica Pecan Bitternut hickory Carya cordiformis Nutmeg hickory C. myristicaeformis Water hickory C. aquatica Pecan C. illinoensis Persimmon Common persimmon Diospyros virginiana Poplar Yellow-poplar Liriodendron tulipifera Sassafras Sassafras Sassafras albidum Silk-oak Lacewood Grevillea robusta Sycamore American sycamore Platanus occidentalis Tanoak Tanoak Lithocarpus densiflorus Teak Teak Tectona grandis Tupelo Black túpelo Nyssa sylvatica Swamp túpelo N. sylvatica var. biflora Water túpelo N. aquatica Walnut Black walnut Juglans nigra Willow Black willow Salix nigra Yagrumo hembra Yagrumo hembra Cecropia peltata

UNITED STATES SOFTWOODS Cedar Alaska cedar Alaska-cedar Chamaecyparis nootkatensis Incense cedar Incense-cedar Libocedrus decurrens Port Orford cedar Port-Orford-cedar Chamaecyparis lawsoniana Eastern red cedar Eastern redcedar Juniperus virginiana Western red cedar Western redcedar Thuja plicata Northern white cedar Northern white-cedar T. occidentalis Southern white cedar Atlantic white-cedar Chamaecyparis thyoides Cypress Baldcypress Taxodium distichum Pond cypress T. distichum var. nutans

92 NOMENCLATURE OF WOOD SPECIES AND VENEER—continued

Commercial name of veneer Official common Botanical name tree name General Specific

UNITED STATES SOFTWOODS—continued Fir Balsam fir Balsam fir Abies balsamea Douglas-fir Coast Douglas-fir Pseudotsuga menziesii Interior west Douglas-fir P. menziesii Interior north Douglas-fir P. menziesii var. glauca Interior south Douglas-fir P. menziesii var. glauca Noble fir Noble fir Abies 'procera White fir Subalpine fir A. lasiocarpa California red fir Abies magnifica Shasta red fir A, magnifica var. shastensis Grand fir A, grandis Pacific silver fir A. amabilis White fir A. concolor Hemlock Eastern hemlock Eastern hemlock T. canadensis Mountain hemlock Mountain hemlock T. mertensiana West Coast hemlock Western hemlock T. heterophylla Juniper Western juniper Alligator juniper Juniperus deppeana Rocky Mountain juniper J. scopulorum Western juniper J. occidentalis Western larch Western larch Larix occidentalis Pine Digger pine Digger pine Pinus sabiniana Jack pine Jack pine P. banksiana Jeffrey pine Jeffrey pine P. jeffreyi Knobcone pine Knobcone pine P. attenuata Limber pine Limber pine P. flexilis Lodgepole pine Lodgepole pine P. contorta Norway pine Red pine P. resinosa Ponderosa pine Ponderosa pine P. ponderosa Sugar pine Sugar pine P. lambertiana Idaho white pine Western white pine P. monticola Northern white pine Eastern white pine P. strobus White bark pine White bark pine P. albicaulis Southern pine Loblolly pine Pinus taeda Shortleaf pine P. echinata Longleaf pine P. palustris Slash pine P. elliottii Spruce pine P. glabra Pond pine P. serótina Virginia pine P. virginiana Pitch pine P. rigida Sand pine P. clausa Table-Mountain pine P. pungens Redwood Big tree Sequoia gigantea Redwood S. sempervirens Spruce Eastern spruce Black spruce Picea mariana Red spruce P. rubens White spruce P. glauca Engelmann spruce Blue spruce P. pungens Engelmann spruce P. engelmannii Sitka spruce Sitka spruce P. sitchensis Tamarack Tamarack Larix laricina Pacific yew Pacific yew Taxus brevifolia

OTHER SPECIES IMPORTANT TO U.S. VENEER Alpine ash Alpine ash Eucalyptus gigantea Angélique Angélique Dicorynia guianensis Apitong Keruing Dipterocarpus spp. Avodire Avodire Turracanthus africanus Brazil nut Brazil nut Bertholletia excelsa Bubinga Bubinga Guibourtia spp. Cativo Cativo Prioria copaifera

93 NOMENCLATURE OF WOOD SPECIES AND VENEER—continued

Commercial name of veneer Official common Botanical name tree name General Specific

OTHER SPECIES—continued Ceiba Ceiba Ceiba pentandra and samauma Determa Determa Ocotea rubra Kapur Keladan Dryobalanops spp. Keruing Apitong Dipterocarpus spp. Klinki Klinki pine Araucaria klinkii Lauan Philippine mahogany Dark red Tangile Shorea polysperma Light red Almon S. almon Light red Bagtikan Parashorea plicata Light red Mayapis S. squamata Limba Limba Terminalia superba Mahogany Honduras mahogany Swietenia macrophylla African mahogany Khaya spp. Mengkulang Mengkulang Tarrietia spp. Meranti Meranti Shorea spp. Mersawa Palosapis Anisoptera spp. Muritinga Muritinga Maquira spp. Okoume Okoume Aucoumea klaineana Paldao Paldao Dracontomelon spp. Primavera Primavera Cybistax donnell-smithii Rosewood Rosewood Dalbergia spp. Sapele Sapele Entandrophragma cylindricum Teak Teak Tectona grandis Caribbean pine Caribbean pine Pinus caribaea Ocote pine Ocote pine Pinus oocarpa

94 APPENDIX II- -PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER

The column on specific gravity of the wood rotary-cut and flat-sliced veneer, while radial gives a quick comparison between species. In shrinkage is an estimate of the widthwise general, the higher the specific gravity, the shrinkage of quarter-sliced veneer. Since these higher the strength properties such as hard- figures are given from green to ovendry, they ness and stiffness and the greater the shrink- can be interpolated for other moisture condi- age. tions. In general, shrinkage is considered to be The green moisture content is given to the a straight-line relationship from a moisture closest 10 percent for both sapwood and heart- content of 30 percent (green) to 0 percent. wood. If the moisture content of the sapwood The volumetric shrinkage, together with spe- and heartwood is very different, it may pay to cific gravity, can be used to describe the wood separate sapwood and heartwood veneer for on the basis of weight at any moisture content. drying. Very high moisture contents, such as The columns describing arrangement and over 100 percent, may indicate problems in cut- size of vessels in hardwood veneer contribute ting and drying veneer from this species. to an understanding of the figure of this ve- Permeability is listed as P, permeable; M, neer. Small pores are under 100 microns in moderately permeable; or jR, refractory. diameter; medium pores 100 to 150 microns; Shrinkage is given under three subheads: and large pores over 150 microns. Tangential, radial, and volumetric. Tangential The grain direction and color of the sap- shrinkage indicates the widthwise shrinkage of wood and heartwood are self-explanatory.

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o 8^ PH §tí 03 M CO S ^ ft 03 O) H >^ 110 APPENDIX III- -MECHAÎVICAL PROPERTIES OF U.S. WOODS FOR VENEER

Seven mechanical properties—tension per- mechanical properties are most important for pendicular to the grain, hardness, modulus of use of veneer in the dry conditions. elasticity, modulus of rupture, compression Most of the mechanical properties listed here parallel to the grain, compression perpendicular came from the Wood Handbook. In some cases, to the grain, and shear—are given in this Ap- the information is from universities or from pendix. The figures for tension perpendicular foreign laboratories. For up-to-date Canadian are taken from green material while the others and U.S. values, it is suggested the reader check are for wood at 12 percent moisture content. American Standards for Testing Materials Tension perpendicular is important during cut- D 2555. ting when the wood is green while the other

MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER

Common name Tension 12 percent moisture content perpen- dicular Hardness Modulus of Modulus Compres- Compres- Shear to (side) elasticity of sion sion parallel grain rupture parallel perpen- to (green) to the dicular grain— grain— to the maximum maximum grain— shearing crushing fiber strength strength stress at pro- portional limit

Lh/in.^ Lb 1,000 Lh/in.^ L6A'w.2 Lh/in.^ Lh/in.^ Lh/in.^

UNITED STATES HARDWOODS Alder Nepal — 510 1,020 8,500 — — Red 390 590 1,380 9,800 5,820 440 1,080 Ash Black 490 850 1,600 12,600 5,970 760 1,570 Blue — 1,290 1,400 13,790 6,980 1,420 2,030 Green 590 1,200 1,660 14,100 7,080 1,310 1,910 Oregon 590 1,160 1,360 12,700 6,040 1,250 1,790 Pumpkin 770 990 1,260 11,060 5,690 1,460 1,720 Shamel — 860 1,660 12,800 — White 590 1,320 1,770 15,400 7,410 1,160 1,950 Aspen Bigtooth 310 420 1,430 9,100 5,300 560 1,080 Quaking 230 350 1,180 8,400 4,250 370 850 Basswood American 280 410 1,460 8,700 4,730 370 990 White — — — — Beech, American 720 1,300 1,720 14,900 7,300 1,010 2,010 Birch Alaskan paper 200 840 1,900 13,800 7,510 830 1,420 Gray — 760 1,150 9,800 4,870 750 1,340 Paper 380 910 1,590 12,300 5,690 600 1,210 River — — .—. — Sweet 430 1,470 2,170 16,900 8,540 1,080 2,240 Yellow 430 1,260 2,010 16,600 8,170 970 1,880 Buckeye Ohio — — — — — Yellow — — 1,170 7,490 4,170 360 960 Butternut 430 490 1,180 8,100 5,110 460 1,170 Cherry, Black 570 950 1,490 12,300 7,110 690 1,700 111 MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER—continued

Common name Tension 12 percent moisture content perpen- dicular Hardness Modulus of Modulus Compres- Compres- Shear to (side) elasticity of sion sion parallel grain rupture parallel perpen- to (green) to the dicular grain— grain— to the maximum maximum grain— shearing crushing fiber strength strength stress at pro- portional limit Lh/in:^ Lh 1,000 Lh/in,' Lh/in.' Lh/in.^ Lb/in.^

UNITED STATEIS HARDWOODS—continued Cottonwood Balsam poplar 160 300 1,100 6,800 4,020 370 790 (Balm of Gilead) Black 270 350 1,270 8,500 4,500 300 1,040 Eastern 410 430 1,370 8,500 4,910 380 930 Swamp Elm American 590 830 1,340 11,800 5,520 690 1,510 Cedar 690 1,320 1,480 13,500 6,020 950 2,240 Rock — 1,320 1,540 14,800 7,050 1,520 1,920 Slippery 640 860 1,490 13,000 6,360 820 1,630 Winged 850 1,540 1,650 14,800 6,780 1,020 2,370 Eucalyptus — 1,330 2,200 15,600 8,200 — — Hackberry 630 880 1,190 11,000 5,440 890 1,590 Hickory, pecan Bitternut __ 1,580 1,790 17,100 9,040 1,680 1,960 Nutmeg — 1,810 1,700 16,600 6,910 1,570 1,850 Pecan 680 1,820 1,730 13,700 7,850 1,720 2,800 Water — — 2,020 17,800 8,600 1,550 — Hickory, true Mockernut 1,970 2,220 19,200 8,940 1,730 1,740 Pignut — 2,140 2,260 20,100 9,190 1,980 2,150 Shagbark — 1,880 2,160 20,200 9,210 1,760 2,430 Shellbark — 1,890 18,100 8,000 1,800 2,110 Holly, American 680 1,020 1,110 10,260 5,540 920 1,710 Honeylocust 930 1,580 1,630 14,700 7,500 1,840 2,250 Koa — 850 1,570 13,300 7,300 — — Laurel, California 780 1,270 940 8,000 5,640 1,130 1,860 Locust, Black 770 1,700 2,050 19,400 10,180 1,830 2,480 Madrone, Pacific — — 1,230 10,450 6,880 1,310 1,810 Magnolia Cucumbertree 440 700 1,820 12,300 6,310 570 1,340 Southern 610 1,020 1,400 11,200 5,460 860 1,530 Maple Bigleaf 600 850 1,450 10,700 5,950 750 1,730 Black 720 1,180 1,620 13,300 6,680 1,020 1,820 Boxelder Red 950 1,640 13,400 6,540 1,000 1,850 Silver 560 700 1,140 8,900 5,220 740 1,480 Sugar — 1,450 1,830 15,800 7,830 1,470 2,330 Oak, red Black 1,210 1,640 13,900 6,520 930 1,910 California black 700 1,100 990 8,700 5,640 1,160 1,470 Cherrybark 800 1,480 2,280 18,100 8,740 1,250 2,000 Chestnut 690 1,130 1,590 13,300 6,830 840 1,490 Laurel 770 1,210 1,690 12,600 6,980 1,060 1,830 Northern red 750 1,290 1,820 14,300 6,760 1,010 1,780 Nuttall Pin 800 1,510 1,730 14,000 6,820 1,020 2,080 Scarlet 700 1,400 1,910 17,400 8,330 1,120 1,890 112 MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER—continued

Common name Tension 12 percent moisture content perpen- dicular Hardness Modulus of Modulus Compres- Compres- Shear to (side) elasticity of sion sion parallel gram rupture parallel perpen- to (green) to the dicular grain— gram— to the maximum maximum gram— shearing crushing fiber strength strength stress at pro- portional limit

Lh/in,' Lh 1,000 Lh/in.' Lh/in} Lh/in,^ Lh/in.'' Lh/in,'^

UNITED STATES HRDWOODS—continued Oak (cont.) Shumard Southern red 480 1,060 1,490 10,900 6,090 870 1,390 Water 820 1,190 2,020 15,400 6,770 1,020 2,020 Willow 760 1,460 1,900 14,500 7,040 1,130 1,650 Oak, white Bur 800 1,370 1,030 10,300 6,060 1,200 1,820 Chinkapin 730 1,190 1,420 12,600 — — — Delta post Durand Live 1,040 2,680 1,970 18,400 8,900 2,840 2,660 Oregon white 940 1,660 1,100 10,320 6,530 1,710 2,020 Overcup 730 1,190 1,420 12,600 6,200 810 2,000 Post 790 1,360 1,510 13,200 6,600 1,430 1,840 Swamp chestnut 670 1,240 1,770 13,900 7,270 1,110 1,990 Swamp white 860 1,620 2,050 17,700 8,600 1,190 2,000 White 770 1,360 1,780 15,200 7,440 1,070 2,000 Ohia 950 2,090 2,370 18,300 8,900 1,400 2,360 Persimmon, common 1,200 2,300 2,010 17,660 9,170 1,990 2,160 Sassafras 520 630 1,120 9,030 4,760 850 1,240 Silk-oak 930 Sugarberry — 960 1,140 9,900 5,620 1,000 1,280 Sweetgum 540 850 1,640 12,500 6,320 620 1,600 Sweetbay — — 1,640 10,920 5,680 560 1,680 Sycamore, American 630 770 1,420 10,000 5,380 700 1,470 Tanoak Teak 960 1,130 1,820 13,900 7,900 1,410 1,320 Tupelo Blackgum 570 810 1,200 9,600 5,520 930 1,340 Swamp Water 600 880 1,260 9,600 5,920 870 1,590 Walnut, Black 570 1,010 1,680 14,600 7,580 1,010 1,370 Willow, Black 430 450 1,010 7,830 4,100 430 1,250 Yagrumo hembra — 320 1,090 6,490 3,490 270 — Yellow-poplar 510 540 1,580 10,100 5,540 500 1,190

UNITED STATES SOFTWOODS Cedar Alaska- 330 580 1,420 11,100 6,310 620 1,130 Atlantic white- 180 350 930 6,800 4,700 410 800 Eastern redcedar 330 900 880 8,800 6,020 920 — Incense- 280 470 1,040 8,000 5,200 590 880 Northern white- 240 320 800 6,500 3,960 310 850 Port-Orford- 180 560 1,730 11,300 6,470 620 1,080 Western redcedar 230 350 1,120 7,700 5,020 490 860 Cypress Baldcypress 300 510 1,440 10,600 6,360 730 1,000 Pondcypress 113 MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER—continued

Common name Tension 12 percent moisture content perpen- dicular Hardness Modulus of Modulus Compres- Compres- Shear to (side) elasticity of sion sion parallel grain rupture parallel perpen- to (green) to the dicular gram— gram- to the maximum maximum grain— shearing crushing fiber strength strength stress at pro- portional limit

Lh/in.'^ L6 1,000 Lh/in.^ Lh/in.^ Lh/in.^ Lh/in.^ Ld/in.^

UNITED STATES SOFTWOODS—continued Douglas-fir Coast 300 710 1,950 12,400 7,240 800 1,130 Interior north 340 600 1,790 13,100 6,900 770 1,400 Interior south 250 510 1,490 11,900 6,220 740 1,510 Interior west 290 660 1,820 12,600 7,440 760 1,290 Fir Balsam 180 400 1,230 7,600 4,530 300 710 California red 380 500 1,490 10,400 5,470 610 1,050 Grand 240 490 1,570 8,800 5,290 500 910 Noble 230 410 1,720 10,700 6,100 520 1,050 Pacific silver 240 430 1,720 10,600 6,530 450 1,180 Shasta red Subalpine 400 900 7,100 4,330 490 1,020 White 300 480 1,490 9,800 5,810 530 1,100 Hemlock Eastern 230 500 1,200 8,900 5,410 650 1,060 Mountain 330 740 1,320 11,200 6,840 1,030 1,230 Western 290 540 1,640 11,300 7,110 550 1,250 Juniper Alligator ,160 650 6,700 4,120 1,380 1,042 Rocky Mountain 720 8,310 5,340 890 1,065 Western Larch, Western 330 830 1,870 13,100 7,640 930 1,360 Pine Digger Eastern white 250 380 1,240 8,600 4,800 440 900 Jack 360 570 1,350 9,900 5,660 580 1,170 Jeffrey 260 500 1,240 9,300 5,530 790 1,210 Knobcone Limber 270 430 1,170 9,100 5,290 580 800 Loblolly 260 690 1,800 12,800 7,080 800 1,370 Lodgepole 220 480 1,340 9,400 5,370 610 880 Longleaf 330 870 1,990 14,700 8,440 960 1,500 Pitch 280 620 1,430 10,800 5,940 1,010 1,360 Pond 280 740 1,750 11,600 7,540 1,120 1,380 Ponderosa 310 460 1,290 9,400 5,320 580 1,130 Red 300 560 1,630 11,000 6,070 600 1,210 Sand 380 730 1,410 11,600 6,920 1,030 1,100 Shortleaf 320 690 1,760 12,800 7,070 810 1,310 Slash 400 1,010 2,060 15,900 9,100 1,020 1,730 Spruce — 660 1,230 10,400 5,650 730 1,490 Sugar 270 380 1,200 8,000 4,770 480 1,050 Table-Mountain 320 660 1,550 11,600 6,830 980 1,200 Virginia 400 740 1,520 13,000 6,710 910 1,350 Western white 260 370 1,510 9,500 5,620 440 850 Whitebark Redwood 260 480 1,340 10,000 6,150 700 940 Big tree

114 MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER—continued

Common name Tension 12 percent moisture content

dicular Hardness Modulus of Modulus Compres- Compres- Shear to (side) elasticity of sion sion parallel gram rupture parallel perpen- to (green) to the dicular gram— gram— to the maximum maximum grain- shearing crushing fiber strength strength stress at pro- portional limit

L6/tn.î Lb 1,000 Lh/in.^ Lh/in.' Lb/in.' Lb/in.^ Lh/in.^

UNITED STATES SOFTWOODS—continued Spruce Black 100 520 1,530 10,300 5,320 530 1,030 Blue Engelmann 240 390 1,300 9,300 4,480 410 1,200 Red 220 490 1,520 10,200 5,890 470 1,080 Sitka 250 510 1,570 10,200 5,610 580 1,150 White 220 480 1,340 9,800 5,470 460 1,080 Tamarack 260 590 1,640 11,600 7,160 800 1,280 Yew, Pacific 450 1,600 1,350 15,200 8,100 2,110 2,230

115 APPENDIX IV—SOME PROCESSING VARIABLES OF U.S. WOODS FOR VENEER

Ease of bark removal is based on fall-cut Yellow birch was selected as "typical" for wood debarked by machine. hardwood veneer because this is a well-known The conditioning temperatures are those sug- veneer species and one on which FPL had much gested for cutting veneer about h inch thick. drying data. Besides, the sapwood and heart- The recommended temperatures for rotary cut- wood of yellow birch take about the same time ting take into account the tendency of the to dry. Our data show that no other hardwoods species to develop splits at the ends of the bolts dry much faster than yellow birch. In contrast, during heating. For slicing, the recommended several hardwood species require considerably temperature will often be 10° to 20° F higher longer drying time than yellow birch. So drying than for peeling because splitting is less of a time ratings for hardwoods are either B or C problem when heating flitches for slicing. For softwoods, the comparison is based on the drying of sapwood or heartwood of Douglas- The last columns are rated on an A, B, and fir. The sapwood of Douglas-fir takes signifi- C scale. A indicates that the speciñc property cantly longer drying time than the heartwood. is basically favorable for use as veneer and C The quality and recovery of veneer from all indicates that the particular property may be species is sensitive to the setting of the knife a problem in utilizing the species for veneer. and pressure bar. However, acceptable veneer For example, an A rating for log splitting can be cut from some species with a wider due to heating indicates the species is little af- range of settings than can be tolerated by other fected by heating while a C rating indicates that species. An A rating for sensitivity to settings log end splits are a major problem with this of the knife and pressure bar indicates the species. species tolerates a wide latitude in machine The A, B, and C ratings for drying times are setting; a C rating indicates the species cuts comparative. The time required to dry veneer well only within a narrow range of machine varies widely with species and with the type settings. of dryer being used. For this reason, rather Under defects in drying, an A rating means than give specific times for a specific dryer, a species is relatively free of the characteristics drying times are given in comparison with listed, while a C rating means the veneer from other species—yellow birch for hardwood ve- the species is subject to this particular drying neer and Douglas-fir for softwood veneer. defect.

116 SOME PROCESSING VARIABLES OF U.S. WOODS FOR VENEER

Common name Ease Suggested Aggra- Sensitivity Drying time Defects in drying of conditioning vation to setting bark temperature of log of— Sap- Heart- Buckle Splits Col- removal - split- - wood wood lapse by Rotary Sliced ting Knife Pres- machine 2 due to sure heating bar

UNITED STATES HARDWOODS

Nepal 1 100-140 140-160 A A A B B A A A Red 2 80-140 120-160 B A A B B A A A Ash Black 2 120-140 140-160 B B B B B B A A Blue 2 140-160 160-180 — — — — — — — — Green 2 140-160 160-180 — — — — — — — — Oregon 2 140-160 160-180 — — — — — — — — Pumpkin 2 140-160 160-180 — — — — — — — — Shamel 2 140-160 170-180 B A B B B B B A White 2 140-160 160-180 B B B B B B B A Aspen Bigtooth 1 40-70 40-70 A B A C C B A B Quaking 1 40-70 40-70 A B A C C B A B Basswood American 3 40-70 40-70 A C B B B A A A White 3 40-70 40-70 A C B C C A A A Beech, American 1 160-180 180-190 B B B B B B A A-B Birch Alaskan paper 2 140-160 160-180 B A A B B B B A Gray 2 120-140 140-160 — — — — — — — — Paper 2 120-140 140-160 B B B B B A B A River 2 120-140 140-160 B B B — — A A A Sweet 2 140-160 160-180 B B B B B B A A-B Yellow 2 140-160 160-180 B B B B B B A A-B Buckeye Ohio 1 40-70 40-70 A — — — — — — — Yellow 1 40-70 40-70 A — — — — — — — Butternut 2 70-90 100-200 A C C B B C B A Cherry, Black 2 120-140 150-170 B B B B B B A A Cottonwood Balsam poplar 2 40-70 40-70 A B B C C C B C Black 2 40-70 40-70 A B B C C C B C Eastern 2 40-70 40-70 A B B C C C B C Swamp 2 40-70 40-70 A B B C C C B C Elm American 2 120-140 150-170 B B B C C C B A Cedar 2 160-170 190-200 B B B C C — — — Rock 2 160-170 190-200 B B B C C c B A Slippery 2 120-140 180 then B B B C C c B A 150 Winged 2 160-170 190-200 B B B C C — — — Eucalyptus 2 140-160 180-200 C B B C C B B B Hackberry 1 120-140 140-160 A A A B B A A A Hickory, pecan Bitternut 3 160-180 190-200 C B B B C B B A Nutmeg 3 160-180 190-200 C B B B C B B A Pecan 3 160-180 170-180 C B B B C C B A Water 3 160-180 190-200 C C B C C B B A Hickory, true Mockernut 3 160-180 190-200 C B B B C B B A Pignut 3 160-180 190-200 C B B B C C B A Shagbark 3 160-180 190-200 C B B B C B B A Shellbark 3 160-180 190-200 C B B B C B B A 117 SOME PROc:ESSING VARIABI .ES OF U.S. w-OODS . FOR VENEÎÎR 1—continued

Common name Ease Suggested Aggra- Sensitivity Drying time Defects in drying of conditioning vation to setting bark temperature of log of-- Sap- Heart- Buckle Splits Col- removal - - split- - wood wood lapse by Rotary Sliced ting Knife Pres- machine ^ due to sure heating bar

op op

UNITED STATES HARDWOODS —continued Holly, American 2 150-160 170-180 Honeylocust 3 140-160 180-190 B B B B B A B A Koa — 140-160 160-180 B A B B B B B A Jüaiirei, California 150-160 190-200 B B B C C C B A Locust, Black 3 160-180 180-190 B B B — — B B A Madrone, Pacific 3 150-160 180-190 B B B C C B B A Magnolia Cucumbertree 1 70-120 120-140 A A A — — A A A Southern 1 70-120 120-140 A A A — — A A A Sweetbay 1 70-120 120-140 A A A — — A A A Maple Bigleaf 2 80-120 120-140 B A A B B B B A Black 2 160-180 170-190 B B B B B B B B Boxelder 2 80-120 120-140 — — — — — — — — Red 2 100-140 130-150 B A A C C A A A Silver 2 80-120 120-140 B A A C C B B A Sugar 2 160-190 170-190 A-B C C B B A-B B A-B Oak, red Black 2 140-160 180-200 C B B C C A B A California black 2 140-160 160-180 C B B C C B B A Cherrybark 2 140-160 180-200 C B B C C A B B Chestnut 2 140-160 180-200 C B B C C A B A Laurel 2 140-160 180-200 C B C C C B C C Northern red 2 140-160 180-200 C B B C C B B B Nuttall 2 140-160 180-200 C B B — — — — — Pin 2 140-160 180-200 C B B — — — — — Scarlet 2 140-160 180-200 C B B c c A B — Shumard 2 140-160 180-200 C B B — — — — — Southern red 2 140-160 180-200 C B B c c A B B Water 2 140-160 180-200 C B B c c A C C Willow 2 140-160 180-200 C B B c c A C C Oak, white Bur 2 140-160 180-200 C B B c c — — — Chinkapin 2 140-160 180-200 C B B — — — — — Delta post 2 140-160 180-200 C B B — — — — — Durand 2 140-160 180-200 C B B c c A B — Live 2 160-170 200-210 C B B — c — C — Oregon white 2 140-160 180-200 C — — — — — — — Overcup 2 140-160 180-200 C B B c c B C C Post 2 140-160 180-200 C B B c c — — — Swamp chestnut 2 140-160 180-200 C B B — — — — — Swamp white 2 140-160 180-200 C B B c c A B B White 2 140-160 180-200 C B B c c A B B Ohia 2 170-180 200-210 B B C B B B B A Persimmon, common — 150-200 190-200 C C C B B B B B Sassafras 2 100-120 120-150 — — — — — — — — Silk-oak 2 150-160 170-180 B A A c c A A A Sugarberry 1 120-140 140-160 — — — — — — — — Sweetgum 1 120-140 140-160 A A B c c A B B Sycamore, American 1 120-140 150-160 B A A c c C-B B B 118 SOME PROCESSING VARIABLES OF U.S. WOODS FOR VENEER i—continued

Common name Ease Suggested Aggra- Sensitivity Drying time Defects in drying of conditioning vation to setting bark temperature of log of— Sap- Heart- Buckle Splits Col- removal — split- - wood wood by Rotary Sliced ting Knife Pres- machine ^ due to sure heating bar

UNITED STATES HARDWOODS—continued Tanoak 1 150-160 180-190 C B B C C B C C Teak 2 190-200 200-210 B A B C C A A A Tupelo Blackgum 1 120-140 150-160 A A A C C B A B Swamp 1 120-140 150-160 A A A C C B A B Water 1 120-140 150-160 A A A C C B A B Walnut, Black 2 180 then 180 then B B B B B B A A 150 150 Willow, Black 3 40-70 40-70 B B B C C B B A Yagrumo hembra 2 50-80 70-80 A B A B — B B B Yellow-poplar 1 70-120 120-140 A A A B B A A A

UNITED STATES SOFTWOODS Cedar Alaska- 3 120-140 140-160 B A B B B A A A Atlantic white- 2 60-100 100-130 A A B B B A A A Eastern redcedar 2 140-160 160-180 B C B B A B B A Incense- 3 70-120 70-120 A B B — C A A — Northern white- 2 120-140 140-160 B C C — C A B B Port-Orford- 3 120-160 140-160 B A B B B A A A Western redcedar 3 140-160 160-180 B C C B C A B B Cypress Baldcypress 3 60-120 120-140 A B C C C A B A Pondcypress 3 60-120 120-140 A B C C C A B A Douglas-fir Coast 1 60-140 140-180 A B B B B A B A Interior north 1 60-140 140-180 A B B B B A B A Interior south 1 60-140 140-180 A B B B B A B A Interior west 1 60-140 140-180 A B B B B A B A Fir Balsam 1 70-130 120-150 B B B B C B B A California red 1 70-150 130-160 B B B-C B C B B A Grand 1 70-150 130-160 B B B-C B C B B A Noble 1 70-150 130-160 B B B-C B B-C B B A Pacific silver 1 70-150 130-160 B B B B B-C B B A Shasta red 1 70-150 130-160 B B B-C B C B B A Subalpine 1 70-130 120-150 B B B B C B B A White 1 70-150 130-160 B B B-C C C B B A Hemlock Eastern 2 120-160 160-180 B B C B C B B A Mountain 2 120-160 160-180 B B C B C B B A Western 2 120-160 160-180 B B C B C B B A Juniper Alligator 3 140-160 160-180 B C B B A B C A Rocky Mountain 3 140-160 160-180 B C B B A B C A Western 3 140-160 160-180 B C B B A B C A Larch, Western 3 140-150 160-180 B B B B C A B A 119 SOME PROCESSING VARIABLES OF U.S. WOODS FOR VENEER i—continued

Common name Ease Suggested Aggra- Sensitivity Drying time Defects in drying of conditioning vation to setting bark temperature of log of— Sap- Heart- Buckle Splits Col- removal - split- wood wood lapse by Rotary Sliced ting Knife Pres- machine ^ due to sure heating bar

UNITED STATES SOFTWOODS—continued Pine Digger ]L 60-140 140-180 A B B B B B B A Eastern white ] L 70-120 120-140 A B B B B B B A Jack ]L 70-120 120-140 A B B — Jeffrey ] L 60-140 140-180 A A A B B A B A Knobcone 1 L 60-140 140-180 A B B B — B B A Limber ]L 60-120 120-140 A C B B C B B A Loblolly ]L 120-160 160-180 A B B B B B-C B-C A Lodgepole 1L 60-140 140-180 A A A B C B B A Longleaf 1L 120-160 160-180 A B B B B B B A Pitch ]L 120-160 160-180 A B B B B B B A Pond ]L 120-160 160-180 A B C B B B B A Ponderosa ]L 60-140 140-180 A A A B B A B A Red 1L 70-120 120-140 A B B B B B B A Sand ]L 120-160 140-180 A B B B B B B A Shortleaf ] L 120-160 160-180 A B B B B B B A Slash ]L 120-160 160-180 A B B B B B B A Spruce ]L 120-140 140-160 A B B B B B B A Sugar ]L 60-120 120-140 A B B B C A B A Table- Mountain ]L 120-160 160-180 A B B B B B B A Virginia L 120-160 160-180 A B B B B B B A Western white 1 L 60-120 120-140 A B B B C A B A Whitebark ] L 60-120 120-140 A C B B B B B A Redwood Í5 70-160 160-180 B B C C C A C A Big tree ÍI 70-160 160-180 B B C C C A C A Spruce Black ]L 70-120 120-140 A C B B B B B-C A Blue ]L 70-120 120-140 A C B B B B B A Engelmann ]L 70-120 120-140 A C B B B B B A Red ]L 70-120 120-140 A C B B B B B-C A Sitka ]L 70-120 120-140 A C B B B B B A White :L 70-120 120-140 A C B B B B B-C A Tamarack íI 140-160 150-160 B B B B C B B A Yew, Pacific 160-180 180-200 — B B — B C B A

1 A, species property very suitable for veneer; B, intermediate; and C, less desirable for veneer. 21, species relatively easy to debark; 2, intermediate to debark; and 3, difficult to debark.

120 APPENDIX V- -EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS

An A rating would indicate that the wood is Most information in Appendix V is again résistent to development of a particular char- based on the A, B, and C scale, and expresses acteristic even under a wide range of process- relative ratings. Information in the columns ing conditions. A C rating indicates that the head '^Relative freedom from veneer charac- wood is highly susceptible to this particular teristics originating in log storage and proc- characteristic and should indicate caution in essing'' involves a highly variable set of data. processing to keep this specific characteristic All these characteristics are at least to a degree to a minimum. under the control of the processor.

EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS '

Common name Relative freedom from veneer characteristics originating in log storage and in processing

Sap Mold Iron Oxida- Bacteria SurfaceI irregularities stains stain tive stain Odor Extreme Fuzzy Shell- Rough perme- ing ability

UNITED STATES HARDWOODS Alder Nepal B B B C B B B A A Red A B B C A A B A A Ash Black B B B A A A A A B Blue B B B — — — A A B Green B B B — — — A A B Oregon B B B — — — A A B Pumpkin B B B — — — A A B Shamel B B A A A A A A A White B B B C A A A A B Aspen Bigtooth B C A B C — C A B Quaking B C A B C — C A B Basswood American B B A C A A C A A White B B A C A A C A A Beech, American A B B B A A A A B Birch Alaskan paper B B A B — — B A B Gray A B B C — — — — — Paper A B B C B A A B B River A B B C — — A A B Sweet A B B B A A A A B Yellow A B B B A A A B A Buckeye Ohio — — — C — — — — — Yellow — — — C — — — — — Butternut A B B B A A C A A Cherry, Black A A C B A A A A A Cottonwood Balsam poplar B C A B C — C A B Black B C A B C B C A B Eastern B C A B C B C A B Swamp B C A B C — C A B Elm American A A A B B A B B B Cedar B A A B B A — — — Rock A A A B B A B B B Slippery A A A B B A B B B Winged B A A B B A — — — 121 EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS i—con.

Common name Relative freedom from veneer characteristics originating in log storage and in processing

Sap Mold Iron Oxida- Bacteria Surface irregularities stains stain tive stain Odor Extreme Fuzzy Shell- Rough perme- ing ability

UNITED STATES HARDWOODS—continued Eucalyptus B B C C A A A A B Hackberry C C B C A A B B B Hickory, pecan Bitternut B B B A A A A A C Nutmeg B B B A A A A A C Pecan B A B B A A A A C Water B B B A A A A A C Hickory, true Mockernut B B B A A A A A C Pignut B A B B A A A A C Shagbark B B B A A A A A C Shellbark B B B A A A A A C Holly, American C — — — — — A A A Honeylocust A B B A A A A A B Koa A A B B — — A A B Laurel, California B — B C A A A A B Locust, Black A A C B A A A A B Madrone, Pacific A B B B A A A A A Magnolia Cucumbertree B C A C C B A A A Southern B C A C C B A A A Maple Bigleaf A B B C A A A A B Black A B B C A A A A B Boxelder A B B C — — — — — Red A B B C A A A A B Silver A B B C A A A A B Sugar C B B C A A B A B Oak, red Black A A C C A A A A B-C California black A A C C A A A A B-C Cherrybark A A C C A A A A B-C Chestnut A A C C A A A A B-C Laurel A A C C A A A A B-C Northern red A A C C A A A A B-C Nuttall A A C C A A A A B-C Pin A A C C A A A A A-C Scarlet A A C C A A A A B-C Shumard A A C C A A A A B-C Southern red A A C C A A A A B-C Water A A C C A A A A B-C Willow A A C C A A A A B-C Oak, white Bur A A C C A A A A B-C Chinkapin A A C C A A A A B-C Delta post A A C C A A A A B-C Durand A A C c A A A A B-C Live A A C c A A A A B-C Oregon white A A C c A A A A B-C Overcup A A C c A A A A B-C Post A A C c A A A A B-C Swamp chestnut A A C c A A A A B-C Swamp white A A C c A A A A B-C White A A C c A A A A B-C Ohia A A B B A A A A B Persimmon, Common A A A C A A A A B Sassafras B B C — — — — — —

122 EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS i—con.

Common name Relative freedom from veneer characteristics originating in log storage and in processing

Sap Mold Iron Oxida- Bacteria Surface irregularities stains stain tive stain Odor Extreme Fuzzy Shell- Rough perme- ing ability

UNITED STATES HARDWOODS—continued

Silk-oak A A B A Sugarberry C C C C Sweetgum C C B B B A A B A Sweetbay B C A C C B A A A Sycamore, American B B A A A A A A B Tanoak A A C C A A A A C Teak A A B A A A A A B Tupelo Black B B A C A A A Swamp B B A C A A B Water B B A C A A A Walnut, Black A B C B A A B A A Willow, Black C C B C B B C A B Yagrumo hembra C B B B B B B A A Yellow-poplar C C A B C B B A A

UNITED STATES SOFTWOODS

Cedar Alaska- A A B B A A A A A Atlantic white- C A B B A A B A B Eastern redcedar A A B A A A A A B Incense- A A C B A A B B B Northern white- A A B __ A A B C B Port-Orford- A A B B A A A A A Western redcedar A A C — A A B C B Cypress Baldcypress B B B B B B B C B Pondcypress B B B B B B B C B Douglas-fir Coast A A B A A A A B B Interior north A A B A A A A B B Interior south A A B A A A A B B Interior west A A B A A A A B B Fir Balsam A A A A B B B B B California red A A A A B B B B B Grand A A A A B B B B B Noble A A A B B B B B B Pacific silver A A A A B B B B B Shasta red A A A A B B B B B Subalpine A A A A B B B B B White A A A A B B B B B Hemlock Eastern B B B B B B B C B Mountain B B B B B B B C B Western B B B B B B B C B Juniper Alligator A A B A A A A A B Rocky Mountain A A B A A A A A B Western A A B A A A A A B Larch, Western A A B A A A A B B

123 EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS i—con.

Common name Relative freedom from veneer characteristics originating in log storage and in processing

Sap Mold Iron Oxida- Bacteria Surface irregularities stains Stainíi^*^"i^^ 4-'ï'«'r^xLive stain Odor Extreme Fuzzy Shell- Rough perme- ing ability

UNITED STATES SOFTWOODS —continued Pine Digger C B A B B C A B B Eastern white B B A B B B B B B Jack B B A B B B Jeffrey C B A C B C A A B Knobcone B B A B B B B B B Limber B B A B B B C B B Loblolly C C A A B C A B B Lodgepole B B A B B B B A A Longleaf C C A A B C A B B Pitch C C A A B C A B B Pond C C A A B C A B B Ponderosa C B A C B C A A B Red B B A A B B B B B Sand C C A A B C A B B Shortleaf C C A A B C A B B Slash C C A A B C A B B Spruce C C A A B C A B B Sugar B B A C B C B B B Table-Mountain C C A A B C A B B Virginia C C A A B C A B B Western white B B A C B C B B B Whitebark B-C B A B B B C B B Redwood A A C B A A B C B Big tree A A C B A A B C B Spruce Black B B A A A A C B B Blue B B A A A A C B B Engelmann B B A A A A C B B Red B B A A A A C B B Sitka B B A A A A C B B White B B A A A A C B B Tamarack A A B A A A B B B Yew, Pacific — — — — A A A A B 1 A, good—species resists development of undesirable characteristics under a wide range of operating conditions; B, species intermediate in resistance and C, poor—species susceptible to this undesirable development.

124 APPENDIX VI—APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER

The last five columns of the Appendix VI uct, and a C rating indicates the species is gen- table in a sense summarize all the data. An A erally not suited for the particular end product. rating indicates the species is well suited for In making these classifications, the following the indicated product. A B rating indicates the broad criteria were considered : species is moderately well suited for this prod-

End Use Typical Specific Uses Desirable Veneer Qualities Construction plywood Building construction as High stiffness and subfloor, wall sheathing, strength, moderate weight, roof sheathing, concrete and readily glued forms, and overlaid panels. Decorative face Prefinished decorative Attractive figure and veneer wall panels, furniture, color, moderately hard, flush doors, kitchen and readily glued cabinets, and case goods Inner plies for Inner plies for prefinished Low weight, low shrinkage, decorative panels wall panels, furniture, flush straight grain, fine uniform doors, kitchen cabinets, and grain, and easily glued case goods Container veneer Wirebound boxes, bushel High in stiffness, shock and plywood baskets, paper-overlaid resistance, and resistance veneer, cleated panel boxes, to splitting, light color, free and plywood-sheathed crates from odor and taste, and moderate in weight In some instances additional end uses and comments are listed under "other."

125 APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER

Common name Clear Figure of veneer Relative suitability for—2 ve- neer 1 Rotary- and flat-sliced Quarter- and rift-sliced Con- Decor- Inner Con- Other struc- ative plies tainer tion face of veneer ply- veneer decor- and wood ative ply- panels wood

UNITED STATES HARDWOODS Alder Nepal Faint growth ring. Scattered large flakes A-B Large rays slightly from wood rays darker than back- ground Red do Occasional large flakes C B B B Ash Black Conspicuous growth Distinct not conspic- B A B A ring, occasional uous growth ring, burls and cross occasional burl figure Blue B .do. do B A B A Green B .do. do B A B A Oregon B .do. do C A B A Pumpkin B .do. do C B C B Shamel A Pronounced parabolas Distinct stripe from B A B A from the wide growth rings. Faint growth rings. Occa- crossbar sional pin knots White A-B Conspicuous growth Distinct not conspic- ring, occasional uous growth ring, burls and cross fig- occasional burl ure Aspen Bigtooth B Faint growth ring Occasional cross figure, A Underlay- silky luster ment plywood Quaking B .do do A ....do.... Basswood American A Faint growth ring Plain, fine texture C C A A White A do do C C A A Beech, American B Faint g owth ring Numerous small flakes B B C A Plywood up to 1/8 inch in flooring height Birch Alaskan paper C Faint growth ring pat- Too small to quarter- A-B tern. Slow grown. slice Many knots and burls Gray C Distinct not conspic- Generally plain. Occa- uous growth ring, sionally wavy occasionally wavy Paper B do do B A-B B B River — do do B B B B Sweet A do do B A B B Yellow A do do B A B B Buckeye Ohio — Faint growth ring, Plain close grain Yellow — do do C C A B Butternut C Faint to moderate Plain; the figure is due C A C C growth ring, very to color and luster lustrous

126 APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER—continued

Common name Clear Figure of veneer Relative suitability for- ve- neer ^ Rotary- and flat-sliced Quarter- and rift-sliced Con- Decor- Inner Con- Other struc- ative plies tainer tion face of veneer ply veneer decor- and wood ative ply panels wood

UNITED STATES HARDWOODS—continued Cherry, Black Faint growth ring, oc- Light colored small B B casional burl, pin ray flecks, satiny knots, and gum luster spots common Cottonwood Balsam poplar B Faint growth ring Plain C B B A Black B do .do. C C B A Eastern B do .do. c C B A Swamp B do .do. c B B A Elm American B Distinct growth ring Faint growth ring B with fine wavy pat- stripe tern within each ring Cedar B do do B A C A Rock B Conspicuous growth Faint growth ring B A C A ring with fine wavy stripe pattern within each ring Slippery do Distinct growth ring B A B A stripe Winged Distinct growth ring Faint growth ring B A C A with fine wavy pat- stripe tern within each ring Eucalyptus B Faint growth patterns. Ribbon grain. Occa- B A-B C B Occasional crossbar. sional crossbar. Many pin knots Many pin knots Hackberry B Conspicuous growth Distinct not conspic- B A-B C A ring uous growth stripe, fine sparkle from small rays Hickory, pecan Bitternut C Distinct not conspic- Faint growth rings, B B uous growth ring, fine rays, occasional almost always dark stripes straight grain Nutmeg C do do B A C B Pecan C do do B A C B Water C do do B A C B Hickory, true Mockernut C do do B A C B Pignut C do do B A C B Shagbark C do do B A C B Shellbark C do do B A C B Holly, American C Very close grain, al- Very plain uniform C A C C most no visible pat- texture tern Honeylocust A Conspicuous growth Distinct not conspic- C ring uous growth ring, occasional mild cross figure Koa Irregular grain, dark Curly, wavy grain, B-C B B-C streaks fiddle-back dark streaks Laurel, California Faint growth ring, Mixture of plain and C occasional burl or highly figured due blisters to mottle, stumps, and burls

127 APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER—continued

Common name Clear Figure of veneer Relative suitability for—2 ve- neer 1 Rotary- and flat-sliced Quarter- and rift-sliced Con- Decor- Inner Con- Other struc- ative plies tainer tion face of veneer ply veneer decor- and wood ative ply panels wood

UNITED STATES HARDWOODS—continued Locust, Black C Distinct growth ring, Distinct not conspic- C B C B dark streaks asso- uous growth ring ciated with borer holes Madrone, Pacific B Faint growth ring, Bland figure is limited C A C B close grain, figure to color changes in due to pigment the heartwood changes in heart- wood Magnolia Cucumbertree A Faint growth ring Plain B C A A Southern A do do B C A A Maple Bigleaf B Faint growth ring, oc- Most plain, occasion- C A B A casional burls, blis- nally curly and ter, curly, and wavy quilted Black A Faint growth ring, oc- Most plain, occasion- B A B A casionally curly, ally curly and wavy, wavy, birdseye small dark rays Boxelder C Faint growth ring, Plain B B C B close grain like the maples Red B Faint growth ring, oc- Most plain, occasion- B B A A casionally curly or ally curly and wavy, wavy, often with small dark rays pith flecks Silver B do do C B A A Sugar A Faint growth ring, oc- do B A B A casionally curly, fiddle-back, birds- eye, wavy Oak, red Black C Conspicuous growth Pronounced flake on B A B B ring, rotary-cut the true quarter and veneer has a watery a narrow flake when figure with great rift cut; distinct not contrast conspicuous growth ring stripe California black C do do B A B B Cherrybark B do do B A B B Chestnut B do do B A B B Laurel C do do B B c B Northern red B do do B A B B Nuttall B do do B A B B Pin C do do B A C B Scarlet B do do B A B B Shumard B do do B A B B Southern red B do do B A B B Water C do do B B c B Willow C do do B B C B Oak, white Bur B do do B B B B Chinkapin B do do B B C B Delta post B do do B A B B Durand B do do B A B B 128 APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER—continued

Common name Clear Figure of veneer Relative suitability for—^ ve- neer 1 Rotary- and flat-sliced Quarter- and rift-sliced Con- Decor- Inner Con- Other struc- ative plies tainer tion face of veneer ply veneer decor- and wood ative ply panels wood

UNITED STATES HARDWOODS—continued Oak, white (cont.) Live C Moderate growth ring Pronounced ray flakes C B C B Oregon white C Conspicuous growth Pronounced flake on c B C B ring, rotary-cut the true quarter and veneer has a watery a narrow flake when figure with great rift cut; distinct not contrast conspicuous growth ring stripe Overcup B do do B B c B Post C do do B B c B Swamp chestnut B do do B A B B Swamp white B do do B A B B White B do do B A B B Ohia B Faint growth ring pat- Poorly defined ribbon B B C B Face for tern. Occasional grain plywood burls flooring Persimmon, common C Distinct not conspic- Occasional ribbon due C A-B C B Laminated uous growth ring to interlocked grain golf club heads Sassafras — Pronounced growth Distinct not conspic- C B C B ring uous growth ring Silk-oak A Faint growth ring pat- Moderate-sized ray B A B B tern flakes lead to the name "lacewood" Sugarberry Conspicuous growth Distinct not conspic- B B C A ring uous growth stripe, fine sparkle from small rays Sweetbay A Faint growth ring Plain B C A A Sweetgum A Faint growth ring, oc- Distinct not pro- B B B A casionally irregular nounced ribbon oc- darker streaks casionally irregular darker streaks Sycamore, American B Faint growth ring Pronounced reddish B A B A flakes up to 1/4 inch in height Tanoak B Plain, occasional burls Inconspicuous wood B B C B rays and occasional burls Teak A Moderate growth Faint growth stripe. B A B B rings, dark irregular dark irregular streaks, occasional streaks, sometimes burls mottled, fiddle- back or curly grain Tupelo Black Faint growth ring Distinct not pro- B B nounced ribbon, low luster Swamp A do do B B B A Water A do do B B B A Walnut, Black B Distinct not conspic- Inconspicuous growth B A B B uous growth ring, stripe, occasional occasional wavy and burl, crotch, curly cross figure 129 APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER—continued

Common name Clear Figure of veneer Relative suitability for—2 ve- neer 1 Rotary- and flat-sliced Quarter- and rift-sliced Con- Decor- Inner Con- Other struc- ative plies tainer tion face of veneer ply veneer decor- and wood ative ply panels wood

UNITED STATES HARDWOODS—continued

Willow, Black B Faint growth ring Plain, fine texture C B-C B B Yagrumo hembra A Plain, moderate-sized Plain C C B-C B Toy air- vessels planes Yellow-poplar A Faint growth ring Plain B B A A

UNITED STATES SOFTWOODS Cedar Alaska- B Faint growth ring None B B A A Small boat parts Atlantic white C Distinct, not conspic- None C B A A uous growth ring Eastern redcedar B-C Distinct growth ring, Faint growth rings. C A B C Cedar many knots, streaks Spike knots in- chests of white sapwood cluded sapwood alternating with purple-red to dark red heartwood Incense- C Faint growth ring Faint growth ring B-C B B B stripe Northern white C do do B-C B B B Port-Orford- A do do B B A A Western redcedar B Distinct, not conspic- do A-B A B-C B Decorative uous growth ring knotty faces and etched veneer Cypress Baldcypress B Conspicuous irregular Distinct, not conspic- A-B A B A growth ring uous growth ring stripe Pondcypress B do do B A B A Douglas-fir Coast A-B Conspicuous growth Distinct, not conspic- A B-C B A-B ring uous growth ring stripe Interior north B do do A B-C B A-B interior south B do do B B-C B A-B Interior west B do do A B-C B A-B Fir Balsam C Distinct, not conspic- Faint growth ring B-C C C A uous growth ring stripe California red B-C Conspicuous growth Distinct, not conspic- A-B C B-C A ring uous growth ring stripe Grand C do do A-B C B-C A Noble B do do A-B C B-C A Pacific silver C do Faint growth ring A-B C B-C A stripe Shasta red B-C do Distinct, not conspic- A-B C B-C A uous growth ring stripe Subalpine C Conspicuous growth do B-C C C A ring 130 APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER—continued

Common name Clear Figure of veneer Relative suitability for— _2 ve- neer 1 Rotary- and flat-sliced Quarter- and rift-sliced Con- Decor- Inner Con- Other struc- ative plies tainer tion face of veneer ply veneer decor- and wood ative ply panels wood

UNITED STATES SOFTWOODS—continued White C do do A-B C B-C A Hemlock Eastern C Distinct, not conspic- Faint growth ring B-C C B-C A-B uous growth ring stripe Mountain c do do B c B A Western B do do A-B c B A Juniper Alligator C Distinct growth ring, Too small to quarter- C c C C many knots, mixed slice white sapwood and light red-brown heartwood Rocky Mountain C do do C c C C Western C do do C c C C Larch, Western B Conspicuous growth Distinct, not conspic- A B C B ring uous growth ring stripe Pine Digger C Distinct, not conspic- Faint growth ring B-C C C B uous growth ring stripe Eastern white B Faint growth ring None B-C A-B B A Decorative knotty faces Jack C Distinct, not conspic- Faint growth ring B-C C C B uous growth ring stripe Jeffrey B do do B A B A Knobcone C do do B-C C C A Limber C Faint growth ring None B-C C C A Loblolly B Conspicuous growth Distinct, not conspic- A C C B ring uous growth ring stripe Lodgepole C Distinct, not conspic- Faint growth ring B B C A Decorative uous growth ring; stripe knotty faint "pocked" ap- faces pearance Longleaf B Conspicuous growth Distinct, not conspic- A C C B ring uous growth ring stripe Pitch C do do B-C C C B Pond B do do B C C B Ponderosa B Distinct, not conspic- Distinct, not conspic- B A B A uous growth ring uous growth ring stripe Red B do Faint growth ring B B C A stripe Sand B Conspicuous growth Distinct, not conspic- B-C C C B ring uous growth ring stripe Shortleaf B do do A C C B Slash B do do A C C B Spruce B do do B-C C C B Sugar A Faint growth ring None B-C A B A Table-Mountain C Conspicuous growth Distinct, not conspic- B-C C C B ring uous growth ring stripe 131 APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER—continued

Common name Clear Figure of veneer Relative suitability for—2 ve- neer 1 Rotary- and flat-sliced Quarter- and rift-sliced Con- Decor- Inner Con- Other struc- ative plies tainer tion face of veneer ply veneer decor- and wood ative ply panels wood

UNITED STATES SOFTWOODS—continued Virginia C do do B-C C C B Western white A Faint growth ring None B A B A Whitebark C do do B-C C C A Redwood A Distinct, not conspic- Faint growth ring A-B A C A Decorative uous growth ring; stripe; occasionally etched occasionally wavy wavy and burl veneer and burl faces Big tree A Distinct, not conspic- Faint growth ring B A C A uous growth ring stripe Spruce Black C Faint growth ring None B-C C C A Blue C do do B-C C C A Engelmann C do do B C C A Red C do do B C C A Sitka B do do A-B B B A Aircraft parts White C do do B-C C C A Tamarack C Conspicuous growth Distinct, not conspic- A-B B C B ring uous growth ring stripe Yew, Pacific C Mild growth ring Not quarter-sliced C A C B figure 1 An A rating indicates veneer logs of the species tend to have a high percent of clear wood, a C rating indicates a low percent of clear wood, and a B is intermediate. 2 A, indicates species is well suited for end product; B, intermediate; and C, generally not well suited for this product.

132 GLOSSARY

Annual growth ring,—The layer of wood growth put Density,—As usually applied to wood of normal cellu- on a tree during a single growing season. In the tem- lar form, density is the mass of wood substance en- perate zone the annual growth rings of many species closed with the boundary surfaces of a wood-plus-voids (e.g., oaks and pines) are readily distinguished because complex having unit volume. It is variously expressed of differences in the cells formed during the early and as pounds per cubic foot, kilograms per cubic meter, or late parts of the season. In some temperate zone species grams per cubic centimeter at a specified moisture con- (black gum and sweetgum) and many tropical species, tent. annual growth rings are not easily recognized. Diffuse-porous wood.—Certain hardwoods in which the Bird peck.—A small hole or patch of distorted grain pores tend to be uniform in size and distribution resulting from birds pecking through the growing cells throughout each annual ring or to decrease in size in the tree. In shape, bird peck usually resembles a slightly and gradually toward the outer border of carpet tack with the point towards the bark; bird peck the ring. is usually accompanied by discoloration extending for Dubbing.—The extra heavy cut that may occur at the considerable distance along the grain and to a much ends of a lathe or slicer knife when it is ground. This lesser extent across the grain. rounds the ends of the knife and is undesirable. Taking Birdseye.—Small localized areas in wood with the fibers up slack in the parts of the grinding machine or use indented and otherwise contorted to form few to many of short dummy knife sections at the ends of the knife circular or elliptical figures remotely resembling birds' during grinding will reduce or eliminate dubbing. eyes on the tangential surface. Sometimes found in Earlywood.—The portion of the annual growth ring sugar maple and used for decorative purposes; rare in that is formed during the early part of the growing other hardwood species. season. It is usually less dense and weaker mechan- ßolt,— (l) A short section of a tree trunk; (2) in ically than latewood. veneer production, a short log of a length suitable for Equilibrium moisture content.—The moisture content peeling in a lathe. at which wood neither gains nor loses moisture when Burl,— (1) A hard, woody outgrowth on a tree, more surrounded by air at a given relative humidity and or less rounded in form, usually resulting from the temperature. entwined growth of a cluster of adventitious buds. Such Extractive,—Substances in wood, not an integral part burls are the source of the highly figured burl veneers of the cellular structure, that can be removed by solu- used for purely ornamental purposes. (2) In lumber or tion in hot or cold water, ether, benzene, or other sol- veneer, a localized severe distortion of the grain gener- vents that do not react chemically with wood compo- ally rounded in outline, usually resulting from over- nents. growth of dead branch stubs, varying from 1/2 inch Fiber saturation point,—The stage in the drying or to several inches in diameter; frequently includes one wetting of wood at which the cell walls are saturated or more clusters of several small contiguous conical and the cell cavities are free from water. It applies to proturberances, each usually having a core or pith an individual cell or group of cells, not to whole boards. but no appreciable amount of end grain (in tangential It is usually taken as approximately 30 percent moisture view) surrounding it. content, based on ovendry weight. Cellulose,—ThQ carbohydrate that is the principal con- Figured veneer,—General term for decorative veneer stituent of wood and forms the framework of the wood such as from crotches, burls, and stumps. cells. Flitch,—A portion of a log sawn on two or more faces Closed sicZe.—Side of veneer not touching knife as it is —commonly on opposite faces, leaving two waney edges. peeled from log (also called tight side of veneer). When intended for resawing into lumber, it is resawn Com6i^ram.—Veneer cut at about a 45° angle to the parallel to its original wide faces. Or, it may be sliced wood rays. The rays show as narrow, straight stripes or sawn into veneer, in which case the resulting sheets on the face of the veneer. White oak is commonly sliced of veneer laid together in the sequence of cutting are to produce combgrain face veneer. Compression wood,—Wood formed on the lower side of called a flitch. The term is loosely used. branches and inclined trunks of softwood trees. Com- Gum.—A comprehensive term for nonvolatile viscous pression wood is identified by its relatively wide annual plant exudates, which either dissolve or swell up in rings, usually eccentric, relatively large amount of contact with water. Many substances referred to as summerwood, sometimes more than 50 percent of the gums, such as pine and spruce gum, are actually oleo- width of the annual rings in which it occurs, and its resins. lack of demarcation between springwood and summer- Hardwoods.—Generally one of the botanical groups of wood in the same annual rings. Compression wood trees that have broad leaves in contrast to the conifers shrinks excessively lengthwise, as compared with or softwoods. The term has no reference to the actual normal wood. hardness of the wood. Crossband,—To place the grain of layers of wood at Heartwood.—The wood extending from the pith to the right angles in order to minimize shrinking and swell- sapwood, the cells of which no longer participate in ing; also, in plywood of three or more plies, a layer the life processes of the tree. Heartwood may contain of veneer whose grain direction is at right angles to phenolic compounds, gums, resins, and other materials that of the face plies. that usually make it darker and more decay resistant Crossfire,—Figure in fancy face veneer caused by the than sapwood. grain of the wood dipping in and out of the face of Latewood.—The portion of the annual growth ring the veneer sheet. that is formed after the earlywood formation has Crotch veneer,—Veneer cut from fork of tree to provide ceased. It is usually denser and stronger mechanically pleasing grain, figure, and contrast. than earlywood. 133 Lignin,—The second most abundant constituent of wood, acterizing the wood of many coniferous species. The located principally in the secondary wall and the mid- term is also applied to synthetic organic products re- dle lamella, which is the thin cementing layer between lated to the natural resins. wood cells. Chemically it is an irregular polymer of Resin ducts,—Intercellular passages that contain and substituted propylphenol groups, and thus no simple transmit resinous materials. On a cut surface, they are chemical formula can be written for it. usually inconspicuous. They may extend vertically para- Mineral streak,—An olive to greenish-black or brown llel to the axis of the tree or at right angles to the discoloration of undetermined cause in hardwoods. axis and parallel to the rays. Moisture content,—The amount of water contained in Short-grain,—Term used for cross grain as when end the wood, usually expressed as a percentage of the grain is exposed on face of veneer. weight of the ovendry wood. Showthrough,—Term used when effects of defects Mold.—A fungus growth on wood products at or near within a panel can be seen on the face. the surface and, therefore, not typically resulting in Sliced veneer,—(See Veneer,) deep discoloration. Mold discolorations are usually ash Softwoods,—Generally, one of the botanical groups of green to deep green, although black is common. trees that in most cases have needlelike or scalelike Oleoresin.—A solution of resin in an essential oil that leaves, the conifers; also the wood produced by such occurs in or exudes from many plants, especially soft- trees. The term has no reference to the actual hard- woods. The oleoresin from pine is a solution of pine ness of the wood. resin (rosin) in turpentine. Specific gravity,—As applied to wood, the ratio of the Parenchyma,—Short cells having simple pits and func- ovendry weight of a sample to the weight of a volume tioning primarily in the metabolism and storage of of water equal to the volume of the sample at a speci- plant food materials. They remain alive longer than the fied moisture content (green, air-dry, or ovendry). tracheids, fibers, and vessel segments, sometimes for Stain.—A discoloration in wood that may be caused by many years. Two kinds of parenchyma cells are recog- such diverse agencies as micro-organisms, metal, or nized—those in vertical strands, known more specific- chemicals. The term also applies to materials used to ally as axial parenchyma, and those in horizontal series impart color to wood. in the rays, known as ray parenchyma. Straight-grained wood,—Wood in which the fibers run Peel,—To convert a log into veneer by rotary cutting. parallel to the axis of the piece. Pitch streaks.—A well-defined accumulation of pitch in Tension wood,—A form of wood found in leaning trees a more or less regular streak in the wood of certain of some hardwood species and characterized by the conifers. presence of gelatinous fibers and excessive longitudinal Plywood.—A composite panel or board made up of shrinkage. Tension wood fibers hold together tenaci- crossbanded layers of veneer only, or veneer in com- ously, so that sawed surfaces usually have projecting bination with a core of lumber or of particleboard fibers, and planed surfaces often are torn or have bonded with an adhesive. Generally the grain of one raised grain. Tension wood may cause warping. or more plies is roughly at right angles to the other Texture,—A term often used interchangeably with plies. grain. Sometimes used to combine the concepts of Pressure bar density and degree of contrast between springwood and Fixed.—A bar on a lathe or slicer set to compress summer wood. the wood just ahead of the knife edge. Veneer,—A thin layer or sheet of wood. Roller,—Used on some lathes in place of a fixed Rotary-cut veneer,—Veneer cut in a lathe which pressure bar and performs the same function. rotates a log or bolt, chucked in the center, against a Quarter-slicing,—A method of cutting face veneer knife. nearly parallel to the wood rays. If the rays are large, Sawed veneer,—Veneer produced by sawing. as in oak, then they are prominent in the face veneer. Sliced veneer,—Veneer that is sliced off a log, bolt, Quarter-slicing also shows interlocked grain to advan- or flitch with a knife. tage in species like mahogany. Veneer checks,—When wood is cut into veneer with a Reaction wood.—Wood with more or less distinctive knife, checks often form on the side of the veneer next anatomical characters, formed typically in parts of to the knife. In general, checks tend to be deeper in leaning or crooked stems and in branches. In hardwoods thick veneer of dense wood than in thin veneer of low- this consists of tension wood and in softwoods of com- density wood. Also called knife checks, lathe checks, pression wood. and slicer checks. Resin,—Inflammable, water-soluble, vegetable sub- Veneer clipper,—Machine for cutting veneers into de- stances secreted by certain plants or trees, and char- sired sizes.

134 INDEX

Abnormal wood, 15 techniques, 29, 74 Adventitious buds, 17, 24 temperatures, 74 Appearance, 125 time, 38, 74,117 veneer, 70 Back grinding, 57 Back-roll lathe, 49 Eccentricity, 14, 24 Bacterial action, 29,121 Electric heating, 44 Bark pockets, 24 Embedded metal, 20, 24 Bark removal, 30,117 End uses, 4,125 Bird peck, 19, 24 Epicormic branches, 17, 23 Bolts for veneer, 31, 51, 68 Extractives, 9, 23 Botanical names, 91 Extraneous cell content, 9 Box shook, 1,125 Bucking into bolts, 31 Faces, 4 Buckle, 3, 83,117 Felling splits, 20 Burls, 17, 24 Figure, 11,17, 23, 34,129 Bushel baskets, 5,125 Fine texture, 23 Fire scars, 19 Case goods, 5,125 Flat-slicing, 32, 49 Checks in veneer, 11 Flitches for veneer, 32, 68 Chucks, 49, 58 Flush doors, 5, 125 Cleated panel boxes, 5, 125 Function of log grades, 13 Clipping veneer, 69 Furniture parts, 2, 5 Close grain, 23 Color, 10,17, 24, 95 Generalized settings, 66 Common names, 91, 95 Grain effects, 8,17, 40, 95 Compression parallel, 23, 111 Grinding : Compression perpendicular, 23, 111 veneer knife, 56 Compression wood, 15, 24 back grinding, 57 Concrete form, 4,125 Growth rate, 7, 24 Conditioning wood, 34, 117 Growth stresses, 15 Construction plywood, 4,125 Gum, 9, 23 Container plywood, 22,125 Gum streaks and pockets, 19 Conveying veneer, 69 Core, 5,125 Half-round cutting, 32, 49 Cracks, quality control, 81 Handling damage, 24 Crossband, 5, 125 Hard deposits, 11, 23 Cutting : Hardness, 23, 111 back cut, 34, 49 Hardwoods, 2 direction, 32 Heat distortion, 51 equipment, 45 Heating : flat-slicing, 32, 49 benefits, 39 half-round, 32, 49 bolts and flitches, 31, 44 quarter-sliced, 34, 49 color changes, 37 rift-cut, 32, 49 decay resistance, 38 rotary, 32, 45 dimensional changes, 37 sawn, 34 disadvantages, 39 slicing, 45 drying time, 38 speed, 53 effects, 34 stay-log, 49 growth stresses, 37 Cylindrical form, 24 hardness, 36 hot water, 40, 42 Debarking, 30,117 plasticity, 34 Decay, 24 rate, 41 Decorative plywood, 3, 125 shrinkage, 38 Core, 4, 125 steam, 40, 42, 44 Crossband, 4, 125 strength, 37 Defects in drying, 117 time required, 40, 41 Diameter effect, 40 torque, 38 Dimensional stability, 11, 23 variability, 40 Dryer : warp, 38 emissions, 74 Hot water heating, 42 fires, 86 types, 72 Ideal veneer log, 12 Drying: Individual species, 91, 95, 111, 116, 121, 125 135 Industrial plywood, 4 construction, 4, 22, 125 Inner plies : 4 industrial, 5, 22, 125 case goods, 4 Plywood-sheathed crates, 5, 125 flush doors, 4 Polyphenols, 10 furniture, 5 Prefinished panels, 5 wall panels, 4 Properties of veneer logs, 11 Irregular grain, 17, 23 Pressure bar: flxed, 60, 65 Kitchen cabinets, 4 generalized setting, 66 Knife: lead for lathe, 61 angle, 48, 59 lead for slicer, 61 back grinding, 57 roller, 60, 65 bevel, 48, 55 setting, 61, 117 generalized settings, 66 setting gap, 63 grinding, 56 terminology, 48 honing, 57 Processing variables, 116, 121 secondary bevels, 57 selection, 54 Quality control: setting, 58,117 slicer, 60 buckle, 83 terminology, 48 casehardening, 86 wear, 55 checks or cracks, 81 thickness, 55 collapse, 86 type, 54 color, 86 Knots, 16, 24 honeycomb, 86 shrinkage, 86 Lathe : stain, 75 advantages, 47, 49, 69 veneer roughness, 79 back-roll, 49 veneer thickness, 75 cutting action, 45 Quarter-sliced, 34, 49 dynamic equilibrium, 53 operation, 45 Requirements for veneer logs, 13 stay-log, 49 Resin, 10, 23 Log: Resistance to splitting, 24 breakdown, 31 Retractable chucks, 50 characteristics, 24 Rift-cut, 32, 49 diameter eccentricity, 14 Ring shake, 16, 24 end splits, 15, 24 Roof sheathing, 4 grades, 13 Rotary cutting, 32, 47, 49, 87 handling damage, 20 processing, 31 Sawing into bolts, 31 requirements, 13 Scars, 24 splits, 29, 41 Seams, 19 storage, 29, 121 Shake, 16 Shear, 23, 111 Mechanical properties, 12, 23, 111 Shelling, 6, 8, 121 Metal stain, 11 Shrinkage, 7, 23, 95 Mineral streak, 24 Slicer: Modulus of elasticity, 23, 111 advantages, 47, 49 Modulus of rupture, 23, 111 dynamic equilibrium, 53 Moisture content, 3, 6, 23, 34, 41, 73, 84, 95, 111 heat distortion, 53 Mold, 121 offset, vertical face, 52 Movement, undesirable: mechanism, 45 wood, 49, 51 parts movement, 52 machine parts, 49, 51 pawl & rächet, 52 stop plate, 52 Names, 91, 95 wood movement, 52 yields, 87 Odor, 11, 23, 29 Slicing techniques, 29, 45, 49 Oleoresin, 10 Species : Overlaid panels, 5 appearance, 125 bark removal, 30 Paper-overlaid veneer, 5 classiñcation for plywood, 22 Parenchyma, 8, 23 density ranges, 22, 95 Peeling techniques, 29 individual, 30, 91 Permeability, 7, 23, 95 log storage, 121 Physical properties of wood, 3, 23, 95 nomenclature, 91 Pitch pockets, 24 processing variables, 116, 121 Plywood : properties, 23 block flooring, 4, 125 specific gravity, 25

136 suitability, 125 conveying and clipping, 69 United States, 21, 25, 91, 95, 111, 116, 125 cutting, 1, 4, 45 Species nomenclature, 91 decorative face, 4, 125 Specific gravity, 3, 23, 25, 41, 42, 95 dryers, 74 Specific uses, 125 drying, 70 Spindles, lathe, 50 figure, 11, 17, 23, 34, 129 Spinout, 38 flitches, 32, 68 Splits, 24, 117 gluability, 4 Spur configuration, 50 hardwoods, 22, 91, 121 Stains, 19, 24, 29, 121 lathe, 49, 69 Stay-log, 49 properties, 70, 95, 111 Steam heating, 42 quality, 2, 4, 75 Storage of logs, 29 roughness, 2, 121 Straight grain, 17, 23 slicer, 49, 69 Stresses, growth, 15 softwoods, 22, 91, 121 Stump pull, 20, 24 species, 91 Subfloor, 4 stiffness, 23, 111 Suitability for use, 125 strength, 23, 111 Surface roughness, 121 thickness,, 2, 76 Sweep, 24 uses, 4, 125 volume, 87 Taper, 24 Veneer logs: Temperature : characteristics, 13, 30 constant, 41 diameters, 13 final, 34, 39, 40 form, 14 gradient, 40 grades, 13 storage, 29 length, 13 total change, 40 properties, 13 Tension perpendicular. 111 sweep, 14 Tension wood, 15, 24 taper, 14 Terminology, 48, 67 Veneer plant requirements, 88 Texture, 8 Veneer yields, 87 Thickness, 2, 76 Volume for plant, 87 Timber requirement, 88 Torque, 38 Wall panels, 4, 125 Tree names, 91 Wall sheathing, 4, 125 Wax, 11, 23 Undesirable movement, 49, 51 Wirebound boxes, 5, 125 Uniformity of thickness, 2, 76 Wood: conditioning, 34, 117 Veneer : movement in cutting, 49 appearance, 125 permeability, 7, 23, 34, 95 buckle, 3, 83 physical properties, 3, 95 characteristics, 121 species, 4, 22, 91 checks, 11 suitability for veneer, 125 color, 17, 24, 95 temperature, 34

"l^ us GOVERNMENT PRINTING OFFICE: 1978 O-24S-770

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