An Adjustable Watch Case Wrench
By Ronald L. Ives
Some of these are thoroughly practical devices; others. although workable, are quite complex in their operation; still others are poor makeshifts, hard to use and likely to scar up the back of the watch.
Study of a large number of these "wrench back" watches brought in for repair disclosed that there are three general types of backs. One type is composed of equilateral polygons, with an even number of sides.
A second is composed of slotted types, with an even number of rim slots. The third type consists of backs drilled or punched. The number of holes is commonly two, three, or four. In addition, a few odd types, having an uneven number of sides or rim slots, are occasionally seen.
Utility of this wrench depends upon the care with which it is made. The adjustments should work smoothly, but with a minimum of shake. If the assembly "weaves" under stress, as it will with loose threads, it is likely to slip off at inopportune moments, scratching the watch back.
Exact dimensions of the wrench are not important, and can be modified to suit materials and conditions, but exact parallelism of the jaws, and tight fit of the feed screw threads, are very important. Threading is best done in a machinist's lathe, to insure exact parallelism.
With this wrench, more than 95 per cent of all wrench back watches seen can be opened provided the back has not been cemented on with fingernail polish. If this has been done, a thorough soaking in acetone or ether may be necessary before the watch can be opened. As a last resort, the back can be heated to loosen it, by the momentary application of a bunsen flame. This is definitely a last resort, and cannot be used on "pot metal" watch backs, as they will melt at quite low temperatures.