Tools, chucks and fixtures

The developments in the design of machine tools during the past ten or fifteen years have brought these machines to a high degree of perfection. Many are provided with features which make it possible to obtain results, both as regards quantity and quality of output, which were practically unheard of a decade ago. It is obvious, however, that no matter how accurate and how well adapted to rapid production a machine may be, comparatively little is gained if the methods of holding the work and presenting the tools to it are not equally well thought out. As a matter of fact, these points are neglected in a great many machine shops. In a few instances we find planning departments and efficient tool-designing departments where the methods and appliances to be used in manufacturing are carefully considered In the majority of shops, however, the workmen, or at best the foremen, are left to devise for themselves the methods by which the work is to be held and machined.

In order to aid these men, as well as the great number of tool-designers regularly employed on work of this character, the articles on tools and holding devices for engine and turret lathes, and horizontal and vertical boring machines, which have been published in MACHINERY by Mr. Albert A. Dowd, have been collected and are now published in this volume. These articles have been recognized as constituting the most fundamental and complete descriptions of tools and devices for machining operations ever published. In addition to the chapters applying specifically to turning and boring operations, considerable attention has been paid to the design of tools and holding devices, with reference to the cost of keeping them in repair considerations which are of prime importance in economical shop management.

A very important feature of this book is that the arbors, chucks, fixtures and other holding devices shown and described are examples of designs actually employed in practice, and successfully applied to productive work in a great number of manufacturing establishments in this country. There is nothing of the theorist in Mr. Dowd's methods of describing the tools, chucks and fixtures dealt with. The descriptions are all plain matter-of-fact statements, and will, therefore, appeal with especial force to the great body of men of practical training who are seeking specific and up-to-date information.

A few of the chapters have already been published in MACHINERY'S well-known 25-cent Reference Books, and the present volume has been brought out in reply to a demand for a more comprehensive and detailed treatment than would be possible in these smaller books. It is the belief of the author and publishers that the work fills a well-defined gap in existing mechanical literature, and that the direct and specific method by which the information contained is given will meet with the approval of the trade for which this book has been prepared.

Standard and Special Tools - The cost of tool equipment for the manufacture of interchangeable work is an item which should be proportionate to the number of pieces to be machined. The saving in time which can be made by the use of special tools should also be carefully considered, as there are many cases where special equipments are designed for work which could be handled to advantage by the judicious use of standard tools. In order to obtain the greatest possible production from their machines, there have been instances where machine tool builders have sold tool equipments of expensive design, when a standard equipment would have done the work very nearly as well. Undoubtedly there was some gain in production, but it is doubtful whether the saving in time would pay for the special tools. The upkeep of special tools is also a factor which must be taken into consideration. It is interesting to note that the present aim of machine tool builders is to so design standard tool equipments that they can be adapted readily to a great variety of working conditions. A great deal of time is spent by manufacturers in devising and experimenting with various tools in order to perfect them to such an extent that they will conform to these conditions.

The rapid growth of the automobile industry in the past ten years is largely responsible for the broader development of our machine tools. The enormous quantities of interchangeable parts which are required in this industry and the manufacturers desire for increased production have brought into existence a great variety of multi-cutting tools. Tools of this kind may be designed for a variety of uses, and tool-holders capable of containing several tools can also be designed for handling a considerable range of work.

Tools for Turret Lathes and Boring Mills - Adjustable tools and those having cutters for turning several diameters are sometimes combined with boring-bars, drills, or cutter heads, these being applied to some one of the various types of turret lathes. They are also occasionally designed for use on a vertical boring mill. When used on the turret lathe, the cut-off slide is frequently equipped with a gang of tools so that the operations of turning, boring and facing can be carried on at the same time. Quite frequently the tools are so arranged that from nine to twelve are working at the same time, with the result that there is a considerable gain in production. There are a great many varieties of so-called "box- tools" on the market, and these are principally used for bar work on turret lathes or screw machines having a collet mechanism. Tools of this type are usually a part of the standard equipment furnished with screw machines adapted to bar work, and they will not be discussed in this book.

Design of Multi-cutting Turning Tools - The design of multi-cutting turning tools for castings and forgings which have several diameters to be machined is a subject well worth considering, for it is safe to say that nearly any manufacturer who uses horizontal or vertical turret lathes can greatly increase the productive efficiency of his machines by the judicious use of multi-cutting tools. The several designs of turning tools illustrated in this chapter have been built for various purposes, and a careful study of the types shown may be of assistance in suggesting methods which can be used to perform some piece of work requiring tools of a similar kind. Some of the important points in the design of tools of this nature are as follows:

1. Rigidity: Avoid overhang as much as possible unless some sort of outboard support can be used. Pilot the tool if practicable.

2. Arrangement of tools: The tools should be perpendicular to the plane in which the turret rotates when indexing, because variations in diameters are less likely to take place when tools are arranged in this way. Unequal indexing of the turret has very little effect on the radial position of the tools under these conditions, so that the sizes can be obtained much more exact than if the tools are placed in a plane parallel to the turret rotation. Use standard rectangular stock for the cutting tools so that the upkeep will be inexpensive and reforging be avoided.

3. Try to make the block containing the tools removable, so that it can be replaced easily by another block with tools arranged differently to handle other work.

4. Make the tool-block adjustable if possible.

5. Back up the tools with adjusting screws.

6. Make provisions so that cutting lubricant can be directed on the faces of the tools when forgings or steel castings are to be machined.

7. Arrange the tool-block in such a way that the thrust of the cut does not come against it; it is much better to have the thrust come on the body of the tool.

Multi-turning Tool for Electric Motor Shafts - One example shown, in Fig. 1 is given of a multi turning tool for bar work. This tool was designed for use on the electric motor shaft shown at A in the illustration. The work was handled in short lengths although the stock is a regular commercial product. Roughing and finishing operations were performed with the same type of tool. The work was held in collet jaws. Something like twenty varieties of shafts having different diameters and shoulder lengths were handled by these tools.


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Tools, chucks and fixtures