Depthing Tool
American Watchmaker and Jeweler (1892)
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
What Has Changed in the Last Century
The depthing tool described in 1892 is still made and sold much as it was then a hinged pair of parallel jaws carrying adjustable runners, used to find the correct centre distance between a wheel and its pinion and scribe it onto the plate; Swiss firms such as Bergeon still list them, and the accuracy checks the American Watchmaker and Jeweler prescribes remain the ones repairers use. What has changed is the work around it: gear trains are now designed and cut by CAD and CNC machinery, and after quartz movements took over the mass market from the 1970s the tool became largely the preserve of restorers and the revived trade in mechanical watches and clocks rather than everyday jobbing repair. On the companion entry, William Derham's "The Artificial Clockmaker" is now generally dated to 1696 rather than "about 1700", and his birthplace is usually given as Stoulton, Worcestershire; he is better remembered today for "Physico-Theology" than for his horology.
Written for this edition, 2026.