Jeweling Caliper Rest
American Watchmaker and Jeweler (1892)
This tool will be found very useful for setting. jewels in plates or settings, in counter sinking for screw heads, opening wheels for pinions or bushings, turning barrel heads, etc. The sliding jaws of the calipers should be so adjusted that when the swinging part is brought back snugly against them, the front cutting edge of the cutter in the sliding spindle will exactly line with the center of the lathe spindle. Then if the calipers are at the right height, when a jewel or jewel setting is placed in the jaws of the caliper it will move the edge of the cutter outward from the lathe center just half the diameter of the jewel then in the caliper, and the cutting made at that distance from the center will exactly coincide with the size of the jewel to be set. If however, if set and worked as above, it is found that the hole cut is too large for the jewel, it will indicate that the calipers are too low down, and should be raised, provision for which is made in the construction of the tool. If on the other hand, the cutting is found too small to fit, it will indicate the calipers should be lowered. The final cutting for the jewel seat should be made by running the center straight inward from the face of the plate; the adjustable screw stop on the back end of the sliding spindle serving to gauge the depth of the cutting.
What Has Changed in the Last Century
When the American Watchmaker and Jeweler described this lathe attachment in 1892, jewels were still commonly rubbed or burnished into a seat cut individually in the plate, which is why the tool's whole purpose was to transfer half the jewel's measured diameter to the cutter. Within a few decades the trade moved to friction-set jewels of standard diameters, pressed into holes opened with a graded reamer, and the bench tool of choice became the dedicated jeweling press with interchangeable reamers, pushers and anvils rather than a caliper rest on the lathe. Watch factories now fit jewels by machine to tolerances of a micron or two, and since the quartz movement went into mass production around 1970 far fewer mechanical movements need this work at all. The caliper rest survives mainly among restorers of antique watches, where the old geometry the entry sets out still holds exactly as written.
Written for this edition, 2026.