Fig. 19. Micrometer for Snap Gages
Fig. 19 shows a form of micrometer that has proved very handy for measuring snap gages, and thicknesses, and can also be used as a small height gage to measure the distance from a shoulder to the base, as shown in Fig. 20. In measuring snap gages or thicknesses, the outside and inside of the measuring disks are used, respectively. This instrument may also come in very handy when setting tools on the planer or shaper. As will be seen in the engraving, there are two sets of graduations on the sleeve A, thus enabling the operator to tell at a glance what measurement is obtained from the outside or the inside of the measuring disks. Each of the disks is 0.100 inch thick, so that the range of the micrometer is 0.800 and 1.000 inch for the outside and inside, respectively. The details of the instrument are as follows:
The sleeve A is composed of the inside measuring disk, the graduated sleeve, and the micrometer nut combined. On the disk are two projections KK, which are knurled, thus providing a grip when operating the tool. The sleeve is threaded on the inside of one end, which acts as a micrometer nut, and the outside of this same end is threaded to receive the adjusting nut D. The sleeve has two slots, each placed 90 degrees from the graduations, and these provide for compensation for wear. The disk part is hardened by heating in a lead bath, and is finished by grinding and lapping. The barrel B is the same as a regular micrometer barrel, and is graduated with 25 divisions. Spindle E consists of the outside disk and the micrometer screw, and the barrel B fits on its end, which is tapped out to receive the speeder C, which serves to hold the barrel in position. The thread is ¼ inch, 40 pitch, and the disk and unthreaded parts are hardened, ground and lapped. To adjust this, instrument, loosen the speeder C and turn the barrel until the proper adjustment is obtained. Then lock the barrel by tightening the speeder again.[[9]]
Fig. 20. Micrometer in Fig. 19 used as Height Gage
Micrometer Caliper Square
Fig. 21 shows an assembled view and the details of a micrometer caliper square which, if accurately made, is equal and often preferable to the vernier caliper now so generally used. One of its advantages over the vernier is that when the measurement is taken, it can be readily discerned without straining the eyes, and this instrument is as easy to manipulate as the regular micrometer.
In the details, part A, which is the main body of the instrument, is made of tool steel, the forward or jaw end being solid with the body. This end is hardened, and the jaw ground and lapped. The body is bored out and two flats milled on the outside, which lighten it up and make it neat in appearance. The jaw end is counterbored out with a 45-degree counterbore to form a bearing for the forward end of the micrometer screw. A slot, ⅛ inch in width, extends from the fixed jaw to the other end, and in this slides the movable jaw C. There are 44 divisions along the side of this slot, each division being 0.050 inch apart, giving the tool a range of 2.000 inches for outside and 2.200 inches for inside measurements. The screw B is the most essential part of this tool, its construction requiring great accuracy. Its diameter is ⅜ inch and it is cut with 20 threads per inch. On its forward end fits the cone F, which is hardened and ground, the round part acting as the forward bearing of the screw and fitting in the 45-degree counterbored hole in the body A. On its other end fits the graduated barrel D and also the speeder G.
Fig. 21. Micrometer Caliper Square