Review by Marvin E. Whitney
Napoleon B. Sherwood was well known and recognized by his peers as a mechanical genius during the mid 1850s. He first worked for the Howard Watch Company and later the Newark Watch Company. During his rather short life (he died at the age of 49 in 1872) he wrote several treatises on various aspects of the watchmaking trade.
It is stated that an Italian, in 1723, first introduced the practice of using gemstones for bearing. Although the art of gem cutting at that time was well understood, no one had attempted to drill a hole in a hard stone small enough for a watch pivot. In this treatise, Sherwood shares his expertise by taking a raw gemstone and describing the steps taken to produce and mount a cap/hole jewel in a watch movement. Although jewels were invented about 1700, their use and manufacture was shrouded in secrecy and suspicion by European guilds until about 1850, when they became widely accepted in the watchmaking trade. So when Sherwood wrote Watch and Chronometer Jeweling, watch jewels as we know them today were not available. As the Smith-Barney ad states, they had to be made “the old fashion way,” for synthetic watch jewels did not make their appearance until 1902 when the Verneuil method of producing artificial crystals of ruby and sapphire was developed.
In Chapter I, Sherwood discusses the characteristic and selection of several gemstones, namely, sapphire, ruby, chrysolite, and aquamarine. The diamond was seldom used except as the upper endstone for marine chronometers. The use here was to prevent the heavy balance from “pitting,” the grinding of a small indentation in the face of the jewel. The balance of a marine chronometer is quite heavy and always runs in a horizontal position, whereas a watch operates in several positions; hence, the pivot would quickly pit a ruby and sapphire. The weight of a watch balance wheel pivot on its cap jewel is in the magnitude of 20,000 - 26,000 pounds per square inch, whereas in a marine chronometer it could be ten times as great.
Chapter II covers the requisite tools, all of simple construction, and how to make them. Splinters of diamonds were mounted in the end of rods for cutters, drills, and chamfers, while smaller pieces were decanted, imbedded in disc saws for cutting with the finer grits being used for grinding and polishing.
In Chapter III and IV, the author explains a sequence of operations that ultimately resulted in the production of the finished jewel mounted in a brilliant finished setting - operations such as sawing the gem piece into various size blanks, grinding/polishing a blank to a desired thickness, and shellacking it to a lathe brassie and then cutting/grinding it into a circular and chamfered disc. While still in the lathe, center was established and a hole was drilled through the blank and the oil sink was cut and polished. Finally, the hole was opened to the desired size with a fine wire charged with diamond powder. All of these operations were completed with simple made diamond cutting hand tools.
Chapter V, “Setting the Jewel,” describes how the setting for the jewel was turned. Having finished the stone, whether it was to be mounted in a plate, cock, or bushing, the setting piece was cemented to a lathe chuck and the hole centered. A recess was turned out, just deep enough to receive the stone, and a circular groove was turned around the hole. Once the jewel was seated in the hole, a small steel conical burnisher was used to force or burnish the thin fillet of metal over the edge of the jewel.
Mr. Sherwood alludes to the fact that the above method was not only tedious but unprofitable if a large number of jewels had to be set, as would be the case in the mass production of watches. Thus, a different mode of operation had to be devised. Mr. Edward Howard, the founder of the famous E. Howard Watch/Clock Company and a very fine craftsman, invented a tool known as a swing or jeweling caliber rest that permitted jewels to be set true without the employment of skilled personnel. Although this tool was invented and manufactured for the purpose of cutting jewel settings, it could be used to countersink screw heads, opening wheels for pinions, bushing, etc.
In conjunction with the above, where many watches were being jeweled each day, it became necessary to diminish the repetition of manipulative operations that slowed production. Thus, in Chapter VI, Sherwood describes an end-shaking tool which controlled the cut of shoulders on jewel setting by gauging the length of the pinion. Sherwood describes its operation with several sketches, which fail to be much help. One of the negative aspects of the book is the few sketches and how poorly they are done.
Sherwood also describes the process of countersinking the jewel setting screw holes and “stripping,” the angle at which the bevel was cut, that not only added to its own brilliancy, but added a great deal when well done to the luster of the jewel. This was achieved with the use of a polished sharpened graver and not by polishing with rouge or other polishing compounds. Sherwood also describes the setting of a rose cut diamond, one which was usually used as the upper endstone/cap jewel of fine watches and always in marine chronometers. The setting of such a jewel requires great skill and tests one’s patience if a perfect job is to be done. The test of character comes once the diamond has been positioned in the cavity of the steel setting. This is because a small steel pointed punch must be used to force the steel gently over the edges of the diamond face, and yet, keeping the face of the diamond perfectly level with the face of the setting. I can certainly attest to the above, for I have been there.
The final Chapter VII, offers several repair hints, such as making screws, making taps for the same, and altering the endshake of a balance staff. Although the art of cutting and use of burnished jewels in watches and chronometers is passe, to the historian and/or restorer, this reprint may prove most interesting and helpful.
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