Tool Making - Markham

A practical treatise on the art of making tools, jigs, and fixtures, with helpful suggestions on heat treatment of carbon and high-speed steels for tools, punches, and dies.

The history of the development of the tool-making art is, of course, the history of the mechanical development of the country. The hand working tools came first and then with the invention of each' successive machine came the creation of tools to go with it. The gradual evolution of machine methods brought an increase in the required accuracy of workmanship and this in turn demanded more precise methods and greater skill on the part of the tool maker. Today, therefore, the large body of so-called "tool makers" represents the most skilled, the most inventive, and the most intelligent of the army of mechanics which forms the back bone of our immense mechanical industries.

Many phases of this mechanical development have increased the importance of the tool maker - the introduction of high-speed steels, demanding greater skill in construction of the tools because of the greater demands upon them; the variation of hardening and tempering methods owing to the variety of steels used; and particularly the use of "production" methods which necessitates the design and manufacture of complicated tools, jigs, and fixtures for the rapid duplication of any given machine. The design of efficient and complete sets of such tools requires highly developed knowledge of machine methods, and a thorough understanding of the machines for which the tools are designed.

The author of this work has had years of experience not only in teaching the subject but in the practical side as well, and is able to give the reader a multitude of helpful suggestions for successfully carrying out the mechanical operations required. It is the hope of the publishers that this work will be found a worthy contribution to our standard technical literature.

As generally understood, a tool-maker is a machinist who has a greater knowledge of the trade than is sufficient simply to enable him to make such machines or parts of machines as may be the regular product of the shop in which he is employed. The business of the tool-maker is to make the tools for producing the different parts of machines, implements, or apparatus. It includes the making not only of cutting tools, but also of jigs and fixtures for holding the work while the various operations are being done, and the necessary gages to determine when the different parts are of correct size and shape. It also includes the making of the models for the different fixtures and gages. In some shops where there is work enough on the gages and models, the tool-makers regularly employed on this latter work are termed gage-makers and model-makers, respectively; yet, in the average shop, it is the tool-maker who makes these tools and such special machinery as may be required.

As generally understood, a tool-maker b a machinist who has a greater knowledge of the trade than is sufficient simply to enable him to make such machines or parts of machines as may be the regular product of the shop in which he is employed.

The business of the tool-maker is to make the tools for producing the different parts of machines, implements, or apparatus. It includes the making not only of cutting tools, but also of jigs and fixtures for holding the work while the various operations are being done, and the necessary gages to determine when the different parts are of correct size and shape. It also includes the making of the models for the different fixtures and gages. In some shops where there is work enough on the gages and models, the tool-makers regularly employed on this latter work are termed gage-makers and model makers, respectively; yet, in the average shop, it is the tool-maker who makes these tools and such special machinery as may be required.

Fundamental Requirements for Successful Work. Accuracy in Vital Measurements. In order to acquire any degree of success, the tool-maker must have not only the ability to work accurately and within reasonable time, but also a knowledge of drafting to enable him to read quickly and exactly any ordinary drawing. Unless he can read decimal fractions readily and correctly, he will experience much difficulty when working to measurements that require accuracy to within .0001 inch. As most of the measuring instruments used by the tool-maker read to .001 inch, and some of them to .0001 inch, or even closer, it will be readily seen that in laying off measurements for gages, models, drill jigs, and similar work, a thorough knowledge of arithmetic is essential.

A tool-maker should be familiar with the accurate reading of the micrometer and of the vernier, as applied to the vernier caliper vernier depth gage, and vernier height gage.

Judgment in Approximate Measurements. While extreme care should be exercised when accuracy b essential, there are parts of a tool where approximate measurements will do. If within 1/16 inch is sufficiently exact, it is folly to spend time to get a dimension within a limit of .0001 inch.

Approximate measurements are those made with the aid of calipers, dividers, surface gage, etc., set to an ordinary steel rule. Precise measurements are obtained by the aid of the various measuring instruments graduated to read to very small fractions of an inch; also by the use of standard reference discs, and standard test bars, accurate within a limit variation of 1/50000 part of an inch. In using the micrometer, the vernier, or any of the measuring instruments supposed to give accurate readings, it is necessary to exercise great care in setting the tools. In setting the vernier, it is well to use a powerful eyeglass in order that any error in setting may be so magnified as to be readily apparent.

Constant Care of Machines. The working parts of any machine that may be running should be kept as clean as possible. Do not allow chips to collect on the shears, V's, of your lathe. If the shears become roughed or worn, accurate turning cannot be done. Keep the machine thoroughly oiled; dean the oil holes out occasionally with a piece of wire, in order that the oil may get to the bearings. Be sure the centers of your lathe are in good condition; have them to gage; and make certain that the live center runs true before taking any finishing cuts. It is advisable to grind the prick punch used in locating working points in some form of a grinder having a chuck or collet to hold the punch while revolving it against the emery wheel; if the point is not perfectly round, it will be impossible to indicate a piece of work perfectly on the faceplate of the lathe with the center indicator.