Practical Treatise on Milling and Milling Machines
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Practical treatise on milling and milling machines Brown & Sharpe Manufacturing Company (Providence, R.I.) ENGINEERING Columbia WLnibevsiitp* intfjcCttpof^ctDgorfe LIBRARY Practical Treatise on Milling and Milling Machines DBS 1919 Edition Brown & Sharpe Mfg. Co* Providence, R. I. u. s. A. Copyright, 1914, by Brown & Sharpe Mfg. Co., Providence, R. I. PREFACE It is our purpose in publishing this book to present, in as non-technical a manner as possible, information that will assist the beginner and practical man to a better understanding of the care and various uses of modern milling machines of the column and knee and manufactur- ing types. CONTENTS CHAPTER I Page Classification of Milling Machines 11 CHAPTER II Essentials of a Modern Milling Machine .... 21 CHAPTER III Erection and Care of Machine 37 CHAPTER IV Spiral Head—Indexing and Cutting Spirals ... 47 CHAPTER V Attachments 69 CHAPTER VI Cutters 89 CHAPTER VII General Notes on Milling, together with Typical Milling Operations 107 CHAPTER VIII Milling Operations—Gear Cutting 149 CHAPTER IX Milling Operations—Cam Cutting, Graduating and Mis- cellaneous Operations 177 TABLES 209 The Original Universal Milling Machine The original universal milling machine was designed primarily for the purpose of forming the flutes in twist drills. Its wonderful capabilities, however, were quickly recognized, and its use soon spread to other lines, until today we find that there is an unusually large variety of machine shop jobs that can be done on a modern machine of this type. Straight and angular pieces, and surfaces of an endless variety of irregular contours, together with spur, bevel and spiral gears, twist drills, etc., can be produced. Also such work as drilling, boring, planing, rack cutting, slotting, cam cutting, graduating, etc., can be successfully accom- plished. In fact, the full variety of work that can be done on a universal milling machine is still unknown, for new ways of using it are being constantly discovered. INTRODUCTION Milling is the process of removing metal with rotary cutters. It is employed extensively in machine shops today for forming parts of machinery, tools, etc., to required dimensions and shapes. A machine designed especially for this purpose was in existence as early as 1818, but little progress was made in the process until after the invention of the universal milling machine (shown on the opposite page) in 1861-62 by Mr. Joseph R. Brown, of J. R. Brown and Sharpe. This was owing chiefly to the difficulties of obtaining satisfactory cutters and of sharpening them. Shortly after this, however, improvements in the methods of making cutters, the invention by Mr. J. R. Brown of the formed cutter which can be sharpened without changing the cutting contour, and the introduction of the grinding wheel for sharpening cutters removed the obstacles that had so seriously hindered the early development of milling. As the field of milling widened, the demands upon the machine increased accordingly, and it became necessary to make certain improvements to adapt it to the new conditions. But it is a note- worthy fact that in all of the changes in design leading up to the modern heavy type of universal machine, shown on page 44, none of the fundamental ideas of the original machine have been lost. Parts have been strengthened to better withstand heavier servipe, and radical changes have been made in the method of driving the spindle and feeds to accommodate the machine to modern requirements. From a comparison of the original machine with a modern type, the important changes that have been made are readily noted. The column has been carried well above the spindle, and an overhanging arm with a support for the outer end of cutter arbor has been added. To further stiffen the arbor, arm braces have been devised by the use of which the overhanging arm, cutter arbor, and knee are all rigidly tied together. These braces on the smaller sizes of machines consist of long slotted cross arms, while on the larger, or heavy service machines, a different and heavier type is employed. Brown & Sharpe Mfg. Co. The table feed has been changed from the end of the feed screw and carried up through the centre of the knee and saddle, thus allowing the table to be swiveled through a much greater arc. Power feeds have been applied to the transverse and vertical table movements, and on large machines a power fast travel for the table has taken the place of the hand quick return. The old-style elevating screw for the knee that required cutting a hole through the floor has been replaced by a telescopic screw. Improvements have been made on the spiral head to make it more rigid and convenient to operate; differential indexing largely replaces the compound method, and refinements such as graduated index sectors, and an adjustable index crank have been added. Such conveniences as permanent handwheels instead of cranks, adjustable dials reading to thousandths of an inch on the feed shafts, and other improvements have been added from time to time. When the milling machine came into more general use, and its possibilities in removing metal began to be appreciated, the demand arose for the ability to make heavier cuts. These demands soon demonstrated that the method of driving the feeds through belts and cone pulleys from the spindle of the machine to the feed mechan- ism, was inadequate. The first improvement was to substitute chain and sprockets for the belt and pulleys and to use removable change gears to provide a variation in the rate of feed. The next step was to place all the change gears in a feed box wherein by simply shifting levers, a wide variation of feeds could be obtained. The main spindle drive has undergone radical changes. The original machine had a four-step cone pulley mounted directly on the spindle, and many of the smaller sizes of machines today are similarly built. In order to get more power and a greater range of speeds, back gears similar to those of a lathe were added. Following these improvements came a radical change in the whole driving mechanism of the machine. The value of feeds that were independent of the spindle speeds had become well recognized, and with the introduction of high speed steel, from which cutters could be made that would take much heavier cuts at faster speeds, and coarser feeds than had ever before been the practice, there arose a demand for more powerful machines. The constant speed type of drive was therefore originated. In this type of machine any combi- nation of table feed and spindle speed is available, because both spindle and feeding mechanisms are driven from the main shaft of Brown & Sharps Mfg. Co. the machine, which revolves at a constant high velocity at all times. The table feeds are therefore entirely independent of the spindle speeds. A powerful drive is also transmitted to the spindle from the driving pulley of large diameter and wide face on the main shaft of the machine through a train of heavy spur gearing in which are certain change gears that can be manipulated to give a wide range of spindle speeds. At the same time that the constant speed type of drive was evolved, the machine was redesigned and made stronger throughout in order to better fit it for the heavy cuts that had become the practice. Later improvements have been the extension of the flat bearing surface on the front of the column to the top, the application of a friction clutch in the driving pulley with levers at the sides of the machine for operating it, the. power fast travel for quick movement of the table, and other improvements of lesser importance. It is not to be assumed that the constant speed type of drive has been developed to the exclusion of the cone type, for there are many pieces of work that can be done to good advantage on this machine. The modern cone type of machine embodies all of the previously mentioned improvements, except those relating particularly to the constant speed drive, and there is still, and probably always will be, a steady demand for this machine. Two other types of machines known as Plain and Vertical Spindle Milling Machines have kept pace with the development of the universal machine. Milling Machines of the Planer and Manufacturing types have also come into extensive use, the former producing a wide range of work that is of too large dimensions for the previously mentioned machines, and the latter manufacturing in large quantities, small duplicate parts of machinery, tools, etc. With the improvements that have been made on the machines and their equipment, milling has become indispensable in the modern shop. Interchangeable pieces can be easily made, and work is pro- duced at a low cost because of the continuous operation and inexpen- siveness of cutters for a given amount of production. We, therefore, recommend the milling machine to manufacturers desirous of obtaining the best results at the lowest cost on all classes of work to which the machine is adapted. And we trust that a careful reading of the follow- ing chapters will be of material assistance in understanding the process of milling and how to use the machines. 10 Brown & Sharpe Mfg. Co. Column and Knee Milling Machine of the Universal Style, Cone Drive Brown & Sharpe Mfg. Co. 11 CHAPTER I Classification of Milling Machines The existing types of milling machines are so numerous, and their designs merge into one another to such an extent, that it is very difficult to classify them definitely. But, taken as a whole, they may be said to consist of two distinct groups, those adapted to a variety of work, and those restricted to the performance of a single operation, such as gear cutting, bolt head milling, thread milling, etc.