VERNIER CALIPER

VERNIER CALIPER The vernier caliper (fig. 2-43) consists of an L- shaped member with a scale engraved on the long shank. A sliding member is free to move on the bar and carries a jaw that matches the arm of the L. The vernier scale is engraved on a small plate that is attached to the sliding member. The vernier caliper can provide very accurate measurements over a large range. It can be used for both internal and external measurement. Some models have a depth reading feature in addition to the internal and external measurements. In using the vernier caliper, you must be able to read a vernier scale. Figure 2-44 shows a bar 1 inch long divided by graduations into 40 parts, so each graduation indicates one-fortieth of an inch (0.025 inch). Every fourth graduation is numbered; each number indicates tenths of an inch (A x 0.025 inch). The vernier, which slides along the bar, is graduated into 25 divisions; these together are as long as 24 divisions on the bar. Each division of the vernier is 0.001 inch smaller than each division of the bar. Verniers that are calibrated as explained previously are known as English-measure verniers. The metric- measure vernier is read the same, except that the units of measurement are in millimeters. Taking Outside Measurements with the Vernier Caliper To measure the distance between outside surfaces or the outside diameter of a round object (such as sound stock or a shaft), steady the object with one hand and hold the caliper in one hand as Figure 2-44.—English-measure vernier scale. shown in figure 2-45. In the figure, the clamping screws are at A and B; the horizontal adjustment screw nut is at C. With A and B loose, slide the movable jaw toward the piece being measured until it is almost in contact. Then tighten clamping screw A to make the fine adjusting nut C operative. Using the fine adjusting nut, adjust the movable jaw to the proper feel, then secure the setting by tightening clamping screw B. The reading can then be taken as previously described. Figure 2-45.—Taking an outside measurement with a vernier caliper. Figure 2-43.—Vernier caliper. 2-28