Fig. 1454.
For finding the centres of bodies or for testing the truth of a centre already marked, the compass calipers shown in [Fig. 1454], are employed. It is composed of one leg similar to the leg of a pair of compasses, while the other is formed the same as the leg of an inside caliper. The uses of the compass calipers are manifold, the principal being illustrated as follows:—
Fig. 1455.
Let it be required to find the centre of a rectangular block, and they are applied as in [Fig. 1455], the curved leg being rested against the edge and a mark being made with the compass leg. This being done from all four sides of the work gives the centre of the piece.
Fig. 1456.
In the case of a hole its bore must be plugged and the compass calipers applied as in [Fig. 1456].