Setting Inside Calipers
Figs. 2 and 3Fig. 4
Setting Inside Calipers
It is customary with most machinists, when setting inside calipers to a scale, to place one end of the scale squarely against the face of some true surface, and then, placing one leg of the caliper against the same surface, to set the other leg to the required measurement on the scale. For this purpose the faceplate of the lathe is frequently used on account of its being close at hand for the latheman. The sides of the jaws of a vise or almost anything located where the light is sufficient to read the markings on the scale are frequently used.
The disadvantages of this method are, first, that a rough or untrue object is often chosen, particularly if it happens to be in a better light than a smooth and true one, and, second, that it is very hard to hold the scale squarely against an object. It is easy enough to hold it squarely crosswise, but it is not so easy a matter to keep it square edgewise. As can be readily seen, this makes quite a difference with the reading of the calipers, particularly if the scale is a thick one.
Figs. 2 and 3 show this effect exaggerated. B is the block against which the scale abuts. The dotted line indicates where the caliper leg should rest, but cannot do so, unless the scale is held perfectly square with the block. Fig. 4 shows a method of setting the calipers by using a small square to abut the scale and to afford a surface against which to place the leg of the caliper. The scale, lying flat on the blade of the square, is always sure to be square edgewise, and is easily held squarely against the stock of the square as shown. This method has also the advantage of being portable, and can be taken to the window or to any place where the light is satisfactory. When using a long scale, the free end may be held against the body to assist in holding it in place.[[2]]
Shoulder Calipers
Fig. 5. Shoulder Calipers