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THE occupation of the toolmaker has steadily grown in importance with the development of manufacturing processes and the general adoption of jigs, fixtures and other special tools by machinery builders to insure interchangeability of product. Where formerly but few men in the shops were directly interested in, for example, the methods by which the holes in a jig could be accurately located and bored, to-day there are thousands of toolmakers who are employing refined processes, precision tools and appliances for executing this class of work.

Many methods and devices originating in watch factories and similar establishments for accomplishing very accurate results were for a considerable period confined almost exclusiv ely to such institutions. These have in later years been found equally serviceable in dealing with work of different charact er and heavier proportions

The master plate, disk, button and refined test indicator processes have been extended from watch-tool to other classes of accurate tool work, and these invaluable adjuncts of the tool room have before them an everbroadening field of usefulness as their practicability becomes more generally appreciated.

Closely allied with these devices, although up to the present time utilized to a comparatively small extent, is the compound microscope which with cross-hairs and conveniently arranged micrometer screws constitutes a testing and measuring appliance having an innumerable number of practical applications in connect ion with the work of the toolmaker.

There is no branch of tool work more important or more interesting than that relating to the construction of jigs and other special tools, in which some of the most ingenious and precise methods known to the skilled machinist are used.

These methods, including the use of master plates, buttons, disks, size blocks, sine bars, etc., have therefore been treated at length, together with processes of making master plates for various purposes, the use of test indicators, accurate gages, the microscope and other appliances.

Considerable space has been devoted to ways and means of dealing with angular and tapered work. The sections pertaining to the latter subjects contain information which should be of service in connectionwith the computing of angles, the finding of distances between hole centers, the lengths of sloping sides and other dimensions frequently required in tool work. The applications of disks and plugs in the measurement of tapers and dovetails are, owing to their importance in this work, also illustrated in detail.

The subject of gage work, always of importance, has become vitally so during the past few years, and the last eight chapters in this book are devoted almost exclusively to gage design and construction, covering methods of making plugs and rings, ring threa d gages, flat gages, snap and other types, gages for automobile parts, and essential devices used by thetoolmaker on this class of work.

The impetus imparted to interchangeable manufacture during recent years has led to the almost universal application of limit gages wherever parts are manufactured in quantities and the work of the toolmaker to-day covers a much wider range of gage operations than ever before.

Along with this growth in the uses of gages in general, the standardization of threaded parts has made necessary a closer degree of attention to varioustypes of thread gages than has heretofore been found except in the most highly developed tool shops and manufacturing plants.

We acknowledge our indebtedness to the authors of various articles incorporated with our own in this book and in footnotes to the various chapters or in the body text it self individual credit is given.