Modern milling machines
MODERN MILLING MACHINESTheir design construction, and working. A handbook for practical men and engineering students.
JOSEPH G. HORNER
LONDON, CROSBY LOCKWOOD AND SON, 1906
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Modern milling machines
PREFACE.
The present period is one of growing specialization in Technical Literature, as in Manufacturing. The books which give a general treatment of a particular subject appeal less to practical men than to students and amateurs. No apology, therefore, is necessary for issuing a work which treats of a single department of machine-shop practice, and one of great and growing importance. Its scope is very broad, as a perusal of the contents of this work will show. Milling machines have become highly specialized, and the work of milling is now subdivided between, different groups of hands just as that of turning is ranging from very plain to very difficult work.
The Author has treated, lightly! those sections of the subject which offer no special difficulties, and has given considerable space to the manufacture of cutters and the work of the machines that call for the exercise of special skill. A number of typical methods of holding work, as well as some fixtures and jigs, are shown, but more as a general guide to the machine-attendant, than with any thought of their covering a field that is immense in its extent and variety. Some of the latest improved machines are illustrated with fully detailed drawings reduced from workshop prints, and special attention has been given to the vexed question of obtaining speeds and feeds.
The thanks of the Author are due to the firms who have kindly supplied drawings and photographs of machines and operations.
The Author has treated, lightly! those sections of the subject which offer no special difficulties, and has given considerable space to the manufacture of cutters and the work of the machines that call for the exercise of special skill. A number of typical methods of holding work, as well as some fixtures and jigs, are shown, but more as a general guide to the machine-attendant, than with any thought of their covering a field that is immense in its extent and variety. Some of the latest improved machines are illustrated with fully detailed drawings reduced from workshop prints, and special attention has been given to the vexed question of obtaining speeds and feeds.
The thanks of the Author are due to the firms who have kindly supplied drawings and photographs of machines and operations.
JOSEPH G. HORNER.
CONTENTS
- THE LEADING ELEMENTS OF MILLING MACHINE DESIGN AND GONSTRUCTION
- PLAIN AND UNIVERSAL MACHINES
- ATTACHMENTS AND BRACINGS
- VERTICAL SPINDLE MACHINES
- PLANO MILLERS OR SLABBING MACHINES
- SPECIAL MACHINES
- CUTTERS
- MILLING OPERATIONS
- INDEXING, SPIRAL WORK, AND WORM, SPUR AND BEVEL GEARS, ETC.
- SPUR AND BEVEL GEARS.
- FEEDS AND SPEEDS.
CHAPTER I - THE LEADING ELEMENTS OF MILLING MACHINE DESIGN AND CONSTRUCTION
The Development of the Milling Cutter - The Utilities of the Milling Machine - The First Machine - Early Improvements - The Influence of the Emery Grinder in its, Development - Existing Machines Classified - The Lincoln Miller - The Characteristics of this Type - Modified Forms - The Work of the Lincoln Miller.
The Development of the Milling Cutter. - The rapid development of milling processes during the lifetime of the present generation is one of the most remarkable and interesting facts in the history of workshop practice. At one time these processes were regarded by engineers of the old school with disfavour, and the belief was very general that they could have but a limited application in the formation of only small surfaces of comparatively simple outlines. Neither would much improvement have been possible but for the fact that the development of emery-grinding machines has kept pace with the elaboration of the milling cutters. Milling, therefore, affords an illustration of ideas long latent, good in themselves, failing of translation into general practice in consequence of necessary conditions not having developed sufficiently.
There is an early, possibly one of the earliest milling cutters in existence in America, made by Vaucanson, a famous French mechanic, born 1709, died 1782. It is pierced with a hexagonal hole, and its profile is approximately that of the cutters for gear- wheel teeth. The pitching of the teeth is very fine, more like that of a saw than a modern milling cutter, and they are irregular.
The difficulties of cutter formation having been got over, there remained another equally great, relating to the construction of the machines. The depth of cut which can be taken by a tool, conditions remaining the same, diminishes with increased breadth of cutting edge. Deep and broad cuts do not coexist. Roughing tools are narrow, the finishing tools are broad. This fact holds good in relation both to single-edged tools, and to milling cutters. One result is that the latter cannot take the deep cuts that the former are capable of doing. More than that, when the width of such cutters increases beyond an inch or two; the stresses are so severe, even with shallow cuts, that vibrations are set up which strain the machines, and detract much from the accuracy of the work. This is the key to the difficulties which have been experienced by the builders and users of milling machines.
The Utilities of the Milling Machine. - The study of the operations of milling machines involves the consideration of a type of rotating tools differing in all respects from those used in drilling and boring. The boring head with cutters has some resemblance to a mill. In fact, some mills with inserted teeth are constructed very similarly to the boring head. But there the resemblance ceases. Mills have a larger number of cutters, and their functions are quite different. Some will bore circular work. But that is not the chief function of milling cutters. Their function is that of universal tools, capable of operating on surfaces plane, curved, regular or irregular, straight or spiral. In short, I can think of no tooling in the machine shop, save that of drilling, which is not also done by means of circular milling cutters. The circular form is, of course, merely a convenient method of arranging a large number of single cutters at equal distances around the axis, the mill being in effect a multiplication of single-cutting tool edges or points, each of which operates in quick succession without any return stroke. The number of teeth and the resulting diameter of a mill are therefore not of a hard-and-fast character, these being details which are settled by practical considerations and convenience. Thus, it would not matter in the case of most jobs whether a mill were 3 or 5 inches diameter, the results in the shape imparted to the work would be the same. Considerations of cost, stability, and class of machine used will determine the choice of one size in preference to that of another.
No milling machine has yet been constructed suitable for all classes of work. There are universal machines, capable of performing all varieties of operations; but they lack the stability necessary for the heaviest work, and the range requisite for many operations. Compromises in milling machines have not been very successful: hence it follows that for nearly every special class of work a special machine is obtainable, and the nature of the jobs to be done should always determine the selection of a machine.
Milling machines are of less value in general engineering shops than in those which deal with specialities. As these machines received their first development in the manufacture of pistols, rifles, sewing machines, and articles of kindred character, so these shops and those of analogous character still afford the best illustrations of the practice of milling. In some manufactories of this kind there will be scores of milling machines performing every conceivable kind of operation on iron, steel, and brass. The wide extent, precision, and economy of the operations performed must, however, be studied in several shops in order to be fully appreciated. In these firms, and others of which these are types, milling is reduced to a system in which interchangeability of parts is secured at a ridiculously low cost per piece. And in proportion as shop systems approach more nearly to these does the value of milling increase. Growing specialization and the increase in number of small fittings are the conditions most favourable to this class of work. Such, however, is the tendency of modern engineering practice, and therefore that practice is favourable to the increasing use and development of the milling machine. Planing," shaping, slotting, all labour under the disadvantages of having a non-cutting return stroke, besides being unsuitable for cutting surfaces which have very irregular contours. And when these last are cut, they cannot be done at once, but must be produced in detail with traverse feeding. In the milling machine, on the contrary, broad surfaces of irregular contours can be cut with mills having those contours, without any traverse feed.
Yet, though it is true that milling lends itself more readily to special work than to that of a general character, the assumption has teen too often hastily made that it has little chance in the general shop. It certainly would be most injudicious to make a radical change in the methods of a general shop already equipped with single-cutting tool machines. But it is wise to introduce milling gradually, beginning with those classes of work for which the long experience of other firms has proved them suitable. In any general shop there are a lot of articles which without doubt can be treated more economically by milling than by any single- tool machine.
DOWNLOAD FREE BOOK:
Modern milling machines
The Development of the Milling Cutter. - The rapid development of milling processes during the lifetime of the present generation is one of the most remarkable and interesting facts in the history of workshop practice. At one time these processes were regarded by engineers of the old school with disfavour, and the belief was very general that they could have but a limited application in the formation of only small surfaces of comparatively simple outlines. Neither would much improvement have been possible but for the fact that the development of emery-grinding machines has kept pace with the elaboration of the milling cutters. Milling, therefore, affords an illustration of ideas long latent, good in themselves, failing of translation into general practice in consequence of necessary conditions not having developed sufficiently.
There is an early, possibly one of the earliest milling cutters in existence in America, made by Vaucanson, a famous French mechanic, born 1709, died 1782. It is pierced with a hexagonal hole, and its profile is approximately that of the cutters for gear- wheel teeth. The pitching of the teeth is very fine, more like that of a saw than a modern milling cutter, and they are irregular.
The difficulties of cutter formation having been got over, there remained another equally great, relating to the construction of the machines. The depth of cut which can be taken by a tool, conditions remaining the same, diminishes with increased breadth of cutting edge. Deep and broad cuts do not coexist. Roughing tools are narrow, the finishing tools are broad. This fact holds good in relation both to single-edged tools, and to milling cutters. One result is that the latter cannot take the deep cuts that the former are capable of doing. More than that, when the width of such cutters increases beyond an inch or two; the stresses are so severe, even with shallow cuts, that vibrations are set up which strain the machines, and detract much from the accuracy of the work. This is the key to the difficulties which have been experienced by the builders and users of milling machines.
The Utilities of the Milling Machine. - The study of the operations of milling machines involves the consideration of a type of rotating tools differing in all respects from those used in drilling and boring. The boring head with cutters has some resemblance to a mill. In fact, some mills with inserted teeth are constructed very similarly to the boring head. But there the resemblance ceases. Mills have a larger number of cutters, and their functions are quite different. Some will bore circular work. But that is not the chief function of milling cutters. Their function is that of universal tools, capable of operating on surfaces plane, curved, regular or irregular, straight or spiral. In short, I can think of no tooling in the machine shop, save that of drilling, which is not also done by means of circular milling cutters. The circular form is, of course, merely a convenient method of arranging a large number of single cutters at equal distances around the axis, the mill being in effect a multiplication of single-cutting tool edges or points, each of which operates in quick succession without any return stroke. The number of teeth and the resulting diameter of a mill are therefore not of a hard-and-fast character, these being details which are settled by practical considerations and convenience. Thus, it would not matter in the case of most jobs whether a mill were 3 or 5 inches diameter, the results in the shape imparted to the work would be the same. Considerations of cost, stability, and class of machine used will determine the choice of one size in preference to that of another.
No milling machine has yet been constructed suitable for all classes of work. There are universal machines, capable of performing all varieties of operations; but they lack the stability necessary for the heaviest work, and the range requisite for many operations. Compromises in milling machines have not been very successful: hence it follows that for nearly every special class of work a special machine is obtainable, and the nature of the jobs to be done should always determine the selection of a machine.
Milling machines are of less value in general engineering shops than in those which deal with specialities. As these machines received their first development in the manufacture of pistols, rifles, sewing machines, and articles of kindred character, so these shops and those of analogous character still afford the best illustrations of the practice of milling. In some manufactories of this kind there will be scores of milling machines performing every conceivable kind of operation on iron, steel, and brass. The wide extent, precision, and economy of the operations performed must, however, be studied in several shops in order to be fully appreciated. In these firms, and others of which these are types, milling is reduced to a system in which interchangeability of parts is secured at a ridiculously low cost per piece. And in proportion as shop systems approach more nearly to these does the value of milling increase. Growing specialization and the increase in number of small fittings are the conditions most favourable to this class of work. Such, however, is the tendency of modern engineering practice, and therefore that practice is favourable to the increasing use and development of the milling machine. Planing," shaping, slotting, all labour under the disadvantages of having a non-cutting return stroke, besides being unsuitable for cutting surfaces which have very irregular contours. And when these last are cut, they cannot be done at once, but must be produced in detail with traverse feeding. In the milling machine, on the contrary, broad surfaces of irregular contours can be cut with mills having those contours, without any traverse feed.
Yet, though it is true that milling lends itself more readily to special work than to that of a general character, the assumption has teen too often hastily made that it has little chance in the general shop. It certainly would be most injudicious to make a radical change in the methods of a general shop already equipped with single-cutting tool machines. But it is wise to introduce milling gradually, beginning with those classes of work for which the long experience of other firms has proved them suitable. In any general shop there are a lot of articles which without doubt can be treated more economically by milling than by any single- tool machine.
DOWNLOAD FREE BOOK:
Modern milling machines
