CRAFTSMEN’S PRACTICE OF TIMBER METHODS

SURVEY AND ANALYSIS OF HISTORICAL AND MODERN METHODS FOR ADJUSTING IRREGULARLY SIZED TIMBER

LASSEN, Ulrik Hjort, Ph.D. Student University of Gothenburg, Sweden, [email protected]

SUMMARY In this paper I have surveyed and classifi ed the different transferring methods used for adjusting irregularly sized timber. In contraty to the research that exists in this fi eld that has mostly focused on buildings and construction types, I have tried to classify and explain the methods that I have identifi ed keeping the focus on what actually happens in the practical situation. It can be seen as an attempt to re-establish the craftsman’s know-how in hands on restoration and reconstruction. The empirical material constists of my own experience and of participation in practical restoration and reconstruction projects in Danish, Norwegian, French, English, Japanese and American timber-frame traditions. I have also used historical and contemporary literature and handbooks for carpenters that involve methods of scribing irregularly sized timber. The preliminary classifi cation of the transferring methods is followed by a visual description of each identifi ed procedure and a short analysis of effi ciency, workplace arrangements, context of tradition, tools and markings for the different methods. Despite advanced power tools, CAD-drawings and prefabrication, every experienced timber framer has undoubtedly found himself in a situation when the transferring methods are effi cient and therefore needed. Even today there will always be situations that require a craftsman’s practice of timber framing methods.

INTRODUCTION

Contrary to Swedish log-building traditions, building with timber-framed structures is today not considered as a part of the Swedish historical know-how. However, the built heritage of Sweden consists of a large number of timber-framed buildings, and the fact is that we today know very little about these constructions and the building methods used. During the last 150 years standard sized materials and precise measures have replaced the necessity for carpenters to master the traditional so- called “scribing” methods of adjusting one asymmetrical material to another. The aim of this paper is to analyse and organize different transferring methods used in timber-framed structures. The survey constitutes a step in my thesis, in which I want to trace, describe and maybe even revive the historical Swedish timber framing techniques. There are different terms for methods used when connecting two irregular timbers in a timber frame construction. Almost every building tradition has a term for the principles of these methods: “scribing” in English, “tilridsning, opsnøring and afbinding” in Danish, “piquage” in French, “aufreissung, austragung and aufscnüren” in German, “dragning” and ”verkplan” in Swedish and ”sumitsuke” in Japanese. Stability, effi ciency and tight fi tting are criteria of quality in this context which are achieved by neutralizing the irregularities of the timbers or by adjusting one timber to the other. These qualities can be achived in different ways, and there are almost as many different solutions as there are different types of constructions. Rule and Scribe Rule (fi g. 1) are two terms used in the English speaking world of timber framers. These two methods are considered almost as contrasts and have in the last decades caused a polarisation within the trade of timber framing. Already in 1836 Edward Shaw found that the Square Rule was less labour intensive and therefore more effi cient than the Scribe Rule [1]. However Shaw only describes two methods within the ”scribing family” called ”Double Cutting” and ”Tumbling”. Will Beemer describes different methods of the scribing family: mapping, tumbling, double cutting, plumb bobbing, bubble scribing [2]. He points out that a skilled timber framer should master more than one of these techniques since they all have advantages in different situations. Rubert Newman shortly describes what he considers as the four most important layout techniques for modern timber framing: Scribe Rule, Square Rule, Mapping and Mill Rule [3]. At a presentation at a timber frame conference in England, Joe Thompson introduces another way of classifying the different methods. Instead of using the term, scribe rule, he puts focus on the transferring process. He suggests a classifi cation into four groups: Plumb Bobbing, Double Cutting, Line Transfer and Square Rule, but he also uses

Square Rule: A smaller, perfect timber is envisioned within a rough outer timber; joints are cut with housings to this inner timber. Pieces can be interchangable. [5] Mill Rule: A layout system for perfect timber dimensions using the face of the timber as reference. [4] Mapping: The irregularities of one timber are identifi ed, measured and transferred to the other timber [2]. Scribe Rule: General term for all methods where each timber is custom-mated to its neighbours. The process requires setting out all the timbers for a given assembly in a framing yard or on a fl oor, positioned relatively as they will ultimately rest in the building. [5] Double Cutting: are cut, preassembled and scribed using the 2 foot mark as reference point. [2] Line Transfer: The face of one timber is transferred onto the other and parallel projected to the position mark [6] Tumbling: The tenon timber is put on the side for marking the position of the shoulders. The face of the mortise timber is extended onto the tenon timber by moving the tenon timber to the position mark [2]. Bubble Scribing: A pair of dividers with cross levels transfers the surface of one timber to the other by keeping the points of the dividers in a fi xed distance vertical above each other [2]. Plumb Bobbing: The Plumb line is used as a reference line vertical to the horizontal timber. The distance between the timber and the plumb line is transferred from one piece to the other [2].

Fig. 1: Nine English terms have been identifi ed in this research (fi g. 1), but there are also important terms in other languages and traditions that also have to be considered, and their signifi cations are to be found in local litterature and handbooks. The methods have different origins but as the conditions often have been more or less the same, it is possible to equalize and thereby organize them theoretically. the terms: vertical and horizontal transfer [4]. The use of the term ”transfer” has inspired me to try to collect and organize the different terms and methods according to the practical situation of a timber framer despite tradition and semantics of words. In this study I will survey and evaluate the methods for adjusting one timber to another in timber frame constructions. The terms and defi nitions are here grouped, as mentioned, in relation to the practical situation and the point of departure is taken from a timber framer’s point of view. Schematic drawings are used to visualize and describe the procedures. The suggested classifi cation will not justify all the qualities of each method, as the methods are results of specifi c construction problems. The survey of the paper consists of four main chapters. First, I present the fundamental principles; the layout drawings, the grid of reference planes in the construction and the use of reference lines on the timber. This provides the basis for understanding the practical situations that are common for all the identifi ed methods. Second, I present the three groups of transferring methods:

1) Vertical Transfer 2) Horizontal Transfer 3) Distance Transfer a) Reference line (fi g. 4) a) Double Cutting (fi g. 10) a) Mapping (fi g. 12) b) Line Transfer (fi g. 6) b) Line Transfer (fi g. 11) b) Square Rule (fi g. 13) c) Transfer of vertical points (fi g. 7) c) Transfer by profi le board (fi g. 16)

These are divided in relation to the practical situation, whereafter they have been divided into two or three subgroups according to the transferring principle. Finally I discuss the value and necessity of this practical knowledge in timber-framing of today.

THE FUNDAMENTAL PRINCIPLES

To understand the difference between the groups of building methods there are some fundamental principles such as reference planes and lines, layout-drawings and workplace arrangements that have to be clarifi ed. In all constructions and working methods used today, there is a need for reference planes. These perfectly fl at planes which bisect the building create a constant theoretical grid that can be seen both on the layout-drawing and in the fi nished construction. Reference planes are found on e.g. the outside of exterior walls, the top of fl oor and in the main cross frames [2]. The reference lines describing these planes are most often placed inside or on the timber revealing the position of the timber in relation to the reference . Most parts in a timber frame construction will refer to at least one reference plane. These reference planes and lines make it possible to neutralize or to transfer shapes and irregularities in the timber. When building an exterior wall, the vertical plane that is fl ush with the outside is used as a reference plane. In log house constructions the building process takes place in the vertical reference plane, by stacking one timber on top of the other adjusting the new timber to the one already in the wall. As all timbers are in a horizontal position this technique works well. As a contrast, building a timber framed wall in the vertical plane is quite elaborate. To be able to mark and cut the timbers during the building process, it would be necessary continuously to stabilize the posts. A way of avoiding these problems in timber framed structures is to make the vertical reference plane horizontal. All vertical reference lines in the building are horizontal during the building process. This principle is probably used in every single method for adjusting irregular timbers, except for the situation when a timber is to be scribed into an existing construction. Establishing the grid of reference planes is necessary before starting the building process. The type of construction, material dimensions, material quality and precision in joints are factors which infl uence the location of the reference planes. Usually a form of construction-drawing plans, sections and/or elevations will show how the primary timbers refer to the reference planes. Depending on which method is to be used, these drawings can be drafts with only the necessary measures or they can be made in scale showing proportions and graphics of the building and the true joint locations. Using practical geometry, plumb and level, trigonometry or a carpenter’s square, it is possible to mark the timbers with reference lines in three dimensions. I have identifi ed fi ve different systems of reference lines used in timber-framed buildings: center lines, datum lines, reference faces, fl oor as reference and parallel lines (fi g. 3). These variations in reference system are closely connected to the different transferring methods, workplace situations, tools and type of construction.

a) b) c) d) e)

Fig. 3: The different types of reference lines: a) Center lines: a vertical and a horizontal line are drawn in both ends. The lines are snapped on the faces of the timber. b) Datum lines: a vertical and a horizontal line are found by the use of the carpenter’s square usually 1½ inch from the chosen reference edge. Lines are snapped on the faces of the timber [7]. c) Reference face: One or two faces of the timber are used as reference lines [6]. d) The fl oor or boards under the timber are used as reference lines and there is no need for markings on the timber [6]. e) Horizontal or vertical lines are projected in parallel when the timber is curved or severely bowed [8]. VERTICAL TRANSFER

In vertical transfer uncut timbers are set over one another in their proper relationships, then irregularities are transferred from one timber to the adjoining one at the joint location [2]. The distance between the horizontal reference lines equals the distance that the timber is dropped. The group of vertical transfer has been divided into three subgroups: the vertical reference line, the vertical line transfer and the transfer of vertical points. The vertical reference line is used to reveal the irregularities of the “vertical” faces of the timbers by placing the plumb line in the corner made by the timbers to be joined (fi g. 4). This principle

1) 2) 3)

Fig. 4: The vertical reference line: 1)Touching the bottom timber in one point the vertical reference line is projected through the corner made by the timbers to be joined. 2) The distances between the reference line and the face of the timber is measured and transferred from the upper timber to the bottom timber and vice versa. 3) The marks are connected into lines or curves that show the projection of the faces of the mating timbers. Tools: , spirit level, carpenter’s square can be used with very irregular or even round timbers. Touching both timbers the line of the plumb bob reveals both faces at the same time. The line is thin and easy to get around for marking the timbers (fi g 5) and compared to the spirit level and the carpenter’s square, that can only reveal one face at the time, the plumb bob must be seen as the most convenient tool for this transferring principle. The measuring of the distance can be done by a pair of dividers [9] or even with a rule, but the more experience you have the more you start working by eye. The use of the plumb bob as the vertical reference line (fi g. 5) is found today in the French “Piquer au Plomb” [10] and in the English/American “Plumb Bobbing” [2 & 3]. It has without doubt also been used in other countries’ building traditions where today the spirit level is in use like e.g. the Norwegian tradition of “sperreverk”. Fig. 5: The French plumb bob The line transfer method consists of extending the direction of the face of the bottom timber onto the top timber, then this direction is projected in parallel to the position mark directly above the true face (fi g. 6). The carpenters square is the most used tool for this transferring principle, but the

1) 2) 3)

Fig. 6: The vertical line transfer: 1) The position of the timbers is transferred by the use of the vertical reference line. 2) The direction of the face of one timber is extended onto the other. 3) A line parallel to the extension of the direction of the face is drawn from the plumb mark. Tools and methods: carpenter’s square, spirit level (plumb bob & straight edge), , tumbling. spirit level can be used for marking the position mark, where there is no fl oor. A bevel gauge can be used for the parallel projection of the direction of the face [6]. The vertical line transfer is found in German, French, Danish and Norwegian traditions [6,11 & 12]. The Japanese method for Lintel setting layout is comparable to Line Transfer, but the extension of the line is done in a slightly different way [13]. The tumbling method from English/American traditions (fi g. 1) is only used where smaller timbers are placed perpendicular to and in between larger timbers [2]. The transfer of vertical points is done by holding two vertical points onto both timbers at the same time. By moving these points, fi xed in a certain distance and constantly kept vertical above each other, the shape of one timber can be drawn onto the adjoining timber (fi g. 7). There are different kinds of dividers that are specially designed for the transfer of vertical points (fi g. 8) and common to all is that the space between the pieces should not be much more than 5 cm. Today the two edges of

1) 2) 3)

Fig. 7: The transfer of vertical points: 1) The bottom timber is pre-cut from the reference lines and measures or a template. 2) The points of the bottom timer are transferred to the top timber by spirit level and measures or simply by eye. 3) The top timber has been cut and the joint is assembled as far as it goes keeping the reference lines of the timbers levelled. The transfer is done with a pair of dividers. Tools: dividers, bubble scriber a or a carpenter’s pencil on top of a rule is often used instead of dividers This method is used in Scandinavian log house traditions and is to be compared to the principle of ”Double Cutting” in the group of horizontal transfer. Every time you have an unsatisfying joint that has to be re-cut for better fi tting you will use this principle of transferring points. The bubble scriber (fi g. 9) is a special pair of dividers with Fig. 8: Different types of cross levels which ensure that the points of the dividers are constantly Norwegian dividers in a vertical position to each other. It has been designed particularly for transferring very irregular shapes with a big distance. The bubble scriber has been developed in the North American log house tradition, and using this method there should be no need for double cutting [2].

HORIZONTAL TRANSFER Fig. 9: Bubble Scriber In horizontal transfer the reference lines of the timbers to be joined are placed horizontally with the reference lines in the same height. The distance between the reference marks or the size of the template used decides how far the tenon is going into the mortise. The group of horizontal transfer has been divided into two subgroups: double cutting and horizontal line transfer. Double Cutting is done by pre-cutting both mortise and tenon and then transferring the shape of the mortise timber to the tenon timber by keeping a fi xed distance in a constantly horizontal position (fi g. 10). This transferring method is mostly used for primary timbers and the transfer is made with a pair of dividers. Double cutting with reference marks as the Danish ”opstik” or the English/American ”2-foot mark” is specifi cally useful in constructions with timbers joined in more than two planes, e.g. DK -“dragerværk” or EN -“jawl-posts”, [1 & 6]. These reference marks are used to keep the timber in the right location, and the distance to be transferred is decided from this marking. 1) 2) 3)

Fig 10: The double cutting: 1) The mortise is pre-cut from the reference lines and measures and the timber is placed in its right location according to the fl oor drawing. 2) The tenon is pre-cut (usually 1-2” short) and pushed into the mortise as far as it goes while the timber is placed along the reference line. 3) The greatest distance between face of the mortise timber and the shoulder of the tenon timber is measured and this distance is transferred all the way round the piece. Tools and Markings: Dividers, 2-foot mark The horizontal line transfer is obtained by placing the timbers horisontally as close to each other as possible. By holding a square or rectangular template onto the face of the mortise timber the direction of the face is transferred to the tenon timber (fi g. 11). The template can be made of 1) 2) 3)

Fig. 11: The horizontal line transfer: 1) The end of the tenon timber is square cut and put as close to the mortise timber as possible following the reference lines on the fl oor. 2) The squared template is put onto the face of the tenon timber with one edge towards the face of the mortise timber. 3) By marking the opposite side of the template the face of the mortise timber is transferred to the tenon timber. Tools: Template, bevel gauge. any board material and the size will often relate to the length of the tenon This method is used for connecting principal in the Danish carpentry tradition [6], and although it today is only used for joining almost perfectly square timber it can be used on any sawn or well hewn surface. Normally the drawing is done on a fl oor or on boards, but the fi rst pair of rafters could be joined and afterwards used as a template for the rest of the frames.

DISTANCE TRANSFER

The third group of transferring methods is distance transfer. Here the position of the timbers is decided in the layout-drawing and marked directly on the timber. There is no contact or closeness necessary between the timbers. The distance marks and reference marks are on the horizontal reference lines on the timber, and the transfer is made by relating to the perpendicular reference lines made with a carpenter’s square or a spirit level. In group of distance transfer has been divided into three subgroups: mapping, square rule and the transfer by profi le board. Mapping is done by holding a vertical reference line onto the face of the mortise timber. The irregularities of the face are identifi ed, measured, remembered and then transferred to the tenon timber (fi g. 12). Mapping is mostly done with a spirit level, but the plumb bob could be used as well. It is generally seen as “the simplest (and potentially least accurate) form of scribing … also called distance scribing, mental scribing or measured scribe” [2]. The shape of very irregular timbers will often be too complicated to memorize and very complex constructions will also be diffi cult to cope with. If there is no room for a full layout (stacked setup) in the workshop, if a mistake occurs and 1) x 2) x 3)

Fig. 12: Mapping: 1) A vertical reference line is hold onto the face of the levelled mortise timber, and the irregularities of the face of the mortise timber are identifi ed, measured and remembered. 2) The irregularities are transferred to the shoulder-to-shoulder mark on the tenon piece by measuring from the vertical reference line. 3) The points are connected showing the projected face of the mortise timber. Tools: Spirit level (plumb bob) one piece does not fi t into its position in the construction or if a timber is going to be exchanged in a restoration project, mapping can be a suitable choice. This is a method that a carpenter would “invent” if the need should occur. The Square Rule consists of visualizing a smaller, perfect timber within a rough outer timber [5]. By measuring from the reference lines, the irregularities are removed from the mortise timber and the tenon timber is prolonged to meet the inner timber (fi g. 13). As the name of the method signifi es,

x x 1) 2) x 3)

Fig. 13: Square Rule: 1) From the timber dimension and the lay-out drawing the dimension of the inner timber is found and marked out from the reference lines. 2) Measuring from the reference lines the housing is marked on each side of the mortise timber for reducing the dimension to the inner timber. 3) The shoulder to shoulder marks, which equal the distance between housings and not the faces, are set out on the tenon timber and squared off. Tools and technical terms: carpenter’s square, housing the carpenter’s square is an essential tool, It can be used for marking out the datum lines, but the most important use is to make the perpendicular (vertical) reference line to the horizontal reference line thus avoiding the need to level the timber when marking out the joints (fi g. 14). The housing (fi g. 15) is a way of reducing the timbers to an ideal dimension only in the specifi c locations where timbers are meeting and thus achieving a tight joinery. By generalizing dimensions and measures, a number of different timbers will have equal dimensions and joints, which makes them interchangeable and which makes the working process very effi cient, as several pieces can be cut in the same time. The digitalized construction Fig. 14: The Carpenter’s square drawings and almost perfect material that are used in the modern timber frame industry has caused that the use of the faces as reference lines has become the probably most used Square Rule method of today. The term “Mill Rule” is a defi nition of layout with no housings [3], which is to be compared with modern construction methods as e.g. balloon framing. The Square Rule method is found in American and Japanese traditions [1 & 8], but today it is probably the most used principle for building timber- framed constructions in the world. Fig. 15: Housing The transfer by profi le board is a way of “mapping” the irregular shapes of the timber. The irregularities of one timber are transferred onto the profi le board and by using the reference lines on the timbers and on the profi le board, the irregularities are transferred onto the mating timber (fi g. 16).

1) 2) 3)

Fig. 16: The transfer by profi le board: 1) A reference line perpendicular to the side is marked on the profi le board, and the round parts of the timber is straightened into . 2) The reference line on the profi le board is held towards the reference line on the timber, and the irregularities are transferred onto the board by extending the bevels with a straight edge or the irregularities simply by eye. 3) The profi le board is held towards the mating timber with the reference lines corresponding to each other, and the lines / shapes are transferred to the timber. Tools: Carpenter’s square, profi le board.

Using the transfer by profi le board it is possible to transfer complex irregularities without the need for direct contact, but mostly round parts of the timber would be facetted to easy the transfer and to be able to extend faces. The use of the profi le board is found in Japanese timber framing traditions [8] where the “Koya Bari beam”, a curved and very irregular timber, is fi tted into a more or less square ruled construction. Round timber is facetted to avoid scribing the joints. This is the only identifi ed tradition using the horizontal reference lines (fi g. 3 e). CONCLUSION

The methods are organized in relation to the the practical situation and according to the different transferring principles. The suggested terminology and the distinction between the different groups can of course be discussed. I have chosen not to use the usual differentiation between the scribe rule and the square rule, as terms have prejudiced signifi cation. To explain the procedure of each method, I have used very schematic illustrations, and a lot of information has been left out. When using one specifi c method the timber framer can chose different tools and reference systems, and therefore the methods have not been easily separated from each other. The workplace arrangements also differ from project to project, so that one method being the perfect choice in one situation would be inappropriate in another, and even within the same projectthe methods would often be used in combination. Usually the tradition and the “savoir faire” of the companies and of the individual timber framer decide which methods to use. The communication of this practical knowledge is not easily done, and for craftsmen familiar with the trade, it is well known that to be able to pass on the practical knowledge of an experienced timber framer you need the practical situation [2]. With this paper I have presented a didactic tool for understanding what actually happens in the practical situation, and hopefully it can be a contribution to the revival of the traditional timber framing methods. The practical knowledge of historic timber framing methods is today barely kept alive. It is therefore essential to communicate this practical knowledge for example in practical educational workshops with authentic projects. There is a need for experienced timber framers who can pass on his or her knowledge to apprentices. At the same time it is important to keep in mind that any specifi c method is not the only way to solve a specifi c problem. Which of these timber-framing methods is the best, most effi cient or most authentic depends on the project. It is also important to realize, that despite advanced power tools, CAD-drawings and prefabrication, every timber framer or carpenter will undoubtedly found himself or herself in situations when the traditional methods of adjusting irregularly sized timber are effi cient, appropriate and therefore needed. In building, today and in the future, there will always be situations that require a craftsman’s experience, knowledge and practice of these old timber-framing methods. REFERENCES

1) SOBON, J. : The Scribe Rule & The Square Rule - Traditional Timber Frame Layout Systems, 1986. 2) BEEMER, W. :Timber Framing for Beginners - X. Introduction to scribing 1-3, printed in the journal ”Timber Framing”, vol. 76-78, 2005. 3) NEWMAN, R. : Timber Framing, Lewes : Guild of Master Craftsman, 2005. 4) Notes from a presentation of THOMPSON, J. at the conference, FRAME 2008, in Essex, UK. 5) BEEMER, W. ROVER, K. Timber Framing for Beginners - VI. A Glossary of Terms, printed in the journal ”Timber Framing” vol. 68, 2003. p.11-17 6) Träsamlinger og lette konstruktioner, Erhvervsskolernes Forlag, Odense, 2005 7) HOLDER, W. : Snap-Line Square Rule Layout, printed in the journal ”Timber Framing” vol. 88, 2008. p. 4-8 8) ANDERSON, M. :Sumitsuke 1-3, printed in the journal ”Timber Framing” vol. 26, 28 & 29, 1993. 9) EMY, A.R. :Traité de l’art de la charpenterie, Paris, 1841 10) LASSEN, U. : Piquer au Plomb - En undersøgelse af en gammel byggeteknik, Göteborgs Universitet, Mariestad, 2007 11) OPDERBECKE, A. :Der Zimmermann (faksimil 1913), Reprint-verl. Leipzig, 1997 12) Husbygging 3, Aschehoug, Oslo, 1954 13) ANDERSON, M. :Japanese Lintel Setting Techniques, printed in the journal ”Timber Framing”, vol. 24, 1992