Modern tool making methods

A treatise on precision dividing and locating methods, lapping, making forming tools, accurat threading, bench lathe practice, tools for precision measurements, and general toolmaking practice.

As the work of the toolmaker requires an unusual degree of skill and refinement and is of great importance in connection with the modem system of interchangeable manufacture, it is surprising that so little has been published heretofore on tool making practice. This volume on "Modern Tool making Methods" is believed to meet a real need as it deals with a great variety of tool-room problems and explains many important Tool making operations. Owing to the varied nature of tool making practice, no attempt has been made to cover completely every phase of work which might properly be classified as tool making. This treatise does, however, cover quite completely those methods and operations which are fundamental and essential to the production of small tools and precision work. It also contains many valuable mathematical rules and typical calculations that will aid in the solution of the practical problems which are so frequently encountered in the tool-room. Some of the methods described represent standard practice, whereas others have been developed by different toolmakers for special operations, and may not prove to be the best under all conditions, because, as every mechanic knows, great accuracy is sometimes necessary regardless of the time required to do the work; whereas, in other cases, the time element is very important. Therefore, any one method may not always prove adequate and it is necessary for the toolmaker to consider the conditions in each case and be guided by his judgment and experience.

As accuracy is essential to practically all tool making operations, the various standard methods for locating, spacing and dividing precision work, have been made a special feature of this book. It also deals with such important subjects as lapping, production of straight and circular forming tools and formed cutters, fluting and grinding milling cutters and reamers, bench lathe practice, precision threading, gaging tools and methods, and many other subjects of practical value.

PRECISION LOCATING AND DIVIDING METHODS

The degree of accuracy that is necessary in the construction of certain classes of machinery and tools, has made it necessary for toolmakers and machinists to employ various methods and appliances for locating holes or finished surfaces to given dimensions and within the prescribed limits of accuracy. In this chapter, various approved methods of locating work, such as are used more particularly in tool-rooms, are described and illustrated.

Button Method of Accurately Locating Work - Among the different methods employed by toolmakers for accurately locating work such as jigs, etc., on the faceplate of a lathe, one of the most commonly used is known as the “button method.” This method is so named because cylindrical bushings or buttons are attached to the work in positions corresponding to the holes to be bored, after which they are used in locating the work. These buttons which are ordinarily about 1/2 or 5/8 inch in diameter, are ground and lapped to the same size, and the ends are finished perfectly square. The outside diameter should preferably be such that the radius can easily be determined, and the hole through the center should be about 1/8 inch larger than the retaining screw so that the button can be adjusted laterally.

As a simple example of the practical application of the button method, suppose three holes are to be bored in a jig-plate according to the dimensions given in Fig. 1. A common method of procedure would be as follows: First lay out the centers of all holes to be bored, by the usual method. Mark these centers with a prick-punch and then drill holes for the machine screws which are used to clamp the buttons. After the buttons are clamped lightly in place, set them in correct relation with each other and with the jig-plate. The proper location of the buttons is very important, as their positions largely determine the accuracy of the work. The best method of locating a number of buttons depends somewhat upon their relative positions, the instruments available, and the accuracy required. When buttons must be located at given distances from the finished sides of a jig, a surface plate and vernier height-gage are often used. The method is to place that side from which the button is to be set, upon an accurate surface plate and then set the button by means of the height-gage, allowance being made, of course, for the radius of the button. The center-to-center distance between the different buttons can afterwards be verified by taking direct measurements with a micrometer (as indicated in Fig. 2) by measuring the overall distance and deducting the diameter of one button.

After the buttons have been set and the screws are tightened, all measurements should be carefully checked. The work is then mounted on the faceplate of the lathe and one of the but- tons is set true by the use of a test indicator. When the dial of the indicator ceases to vibrate, thus showing that the button runs true, the latter should be removed so that the hole can be drilled and bored to the required size. In a similar manner other buttons, are indicated and the holes bored, one at a time. It is evident that if each button is correctly located and set perfectly true in the lathe, the various holes will be located the required distance apart within very close limits.

Locating Work by the Disk Method - Comparatively small precision work is sometimes located by the disk method, which is the same in principle as the button method, the chief difference being that disks are used instead of buttons. These disks are made to such diameters that when their peripheries are in contact, each disk center will coincide with the position of the hole to be bored; the centers are then used for locating the work. To illustrate this method, suppose that the master- plate shown at the left in Fig. 4 is to have three holes a, b and c bored into it, to the center distances given.

Disk-and-button Method of Locating Holes. - The accuracy of work done by the button method previously described is limited only by the skill and painstaking care of the workman, but setting the buttons requires a great deal of time. By a little modification, using what is sometimes called the "disk and button method," a large part of this time can be saved without any sacrifice of accuracy. The disk-and-button method, which was described by Guy H. Gardner in Machinery, September, 1914, is extensively used in many shops. Buttons are used, but they are located in the centers of disks of whatever diameters are necessary to give the required locations. As three disks are used in each step of the process, it is sometimes called the “three-disk method.”