Depthing Tool
A mechanical device for transferring the depthing of a wheel and pinion to a plate, and also for testing the depthing to see if it is correct. The value of a depthing tool depends altogether upon its accuracy, which may be tested by the following method. The joint should be well fitted and move with a light friction. The jaws which carry the centers should open parallel to each other to the full extent of their motion, and the seat for the centers must be parallel with the motion of the jaws and each other as well. The accuracy of the centers may be best tested by means of a micrometer caliper by measuring the centers at various distances apart, and also at the opposite ends of the centers. In any position the measurements should be exactly alike. In the absence of the micrometer caliper the accuracy may be tested by drawing a circle with each set of centers, and with a strong eye-glass examine them and see if they coincide with each other. The variation, if any, will be more marked if the centers are first pushed back as far as possible and then drawing them out to their full extent. When using the tool the centers should be opened by means of the screw sufficiently to clear the work to be inserted, then after the work is in, the tool is carefully adjusted until the depthing is correct. When the correct distance is found the work is to be removed and the centers so set that when the depthing is transferred to the plate they will be at right angles with the plate. If this is not done the depthing will be too shallow in the plate. DERHAM, WILLIAM. An eminent English divine, and one of the early writers on practical horology. He was born at Stourton, near Worcester, in 1657, and died in 1735. He was the author of "The Artificial Clockmaker," a treatise on watch and clock work, showing the art of calculating numbers for all sorts of movements; the way to alter clock work, to make chimes and set them to musical notes, and to calculate and correct the motions of pendulums. It was published about 1700. He was also the author of a work, entitled, "Philosophical