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Articles \ "Watch Glasses"
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"THE WATERBURY" January, 1888
The manufacture of watch crystals is an interesting industry. The glasses, whatever their shape or quality, are cut from glass globes blown to a certain diameter as may be necessary to secure the curve desired.
Arranged about a large room are tables, each lighted by a window. The globes, having been previously blown, are given to the girls at these tables, who begin by gently tapping the glass in such a way as to cause it to crack straight around the bowl, thus separating it in two. Continued taps soon reduce these two portions to strips of concave glass.
Before each girl stands a little apparatus, which works a diamond tool revolving over a thin India rubber plate.
On this plate is placed the strip of glass with the convex surface downward, and on the concave side the diamond tool traces circles very close together, so as to leave as little waste as possible. The girl, with marvelous skill, then completes the rupture by a last tap and removes the disc traced by the diamond. Wherever it is possible to cut in the waste a smaller disc, it is always done, and what finally remains is collected in a box as “cuttings.”
The whole is carried into the checking rooms, weighed and classed. The girl who has received a certain number of globes, weighing so many pounds, must bring back a corresponding number of glasses and a minimum weight of “cuttings.”
In calculating the number of gross yielded, the varying thicknesses and consequent differences of weight in even one globe are taken into account, so that, even at this first stage of the manufacture, a classification by weight is necessary before passing the glasses on to the further series of operations to which they are subjected. This which registers the slightest difference of elevation by a needle moving over a graduated arc.
A great many glasses, known as crystal glasses, are simply bevel-edged, pumiced, polished, packed and sent out.
This straight bevel-edging is done by machinery with a very ingenious apparatus known in the factory as the “small lathe.” The distinctive feature is a flat grindstone turning horizontally and driven by a pulley, likewise horizontal, in front of which the glass, secured between two mandrels, is placed. As the mandrels revolve vertically the glass is rubbed against the horizontally revolving stone in such a way that the friction is equal all round the circumference, so that, if only it has been well centered in the jaws of the lathe, it must come out perfectly round and beveled with mechanical exactitude.
After the beveling, the glasses are returned to the checking-room; here they are carefully examined to see wether the rims have been in any way spoilt from chipping, or wether there still remain any splinters that would prevent the glass from entering in the bezel, etc.; the defects are removed and the watch glass is sent to be packed.