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The Model Engineer and Practical Electrician. February 13, 1930.
the bottom of the sink now formed, and the remaining piece cut right out. By this means there is formed a ledge 5/32nd in. from the outer surface of the plate and 3/32nd in. from the inside of the plate, the back hole being 15/32nd in. in diameter and the inside hole 7/16th in. in diameter. The bushes in which the jewels have been set have now to be turned to be an exact fit into these spaces. It is best to do this in pairs, starting with the 'scape arbor first, fitting first the back and then the front jewel; by so doing the end shake of each arbor can be properly adjusted. The bush is again cemented on the faceplate, and while the shellac is hot, run true by hold- ing a pegwood point in the hole; this must run perfectly true before the brass setting is turned or the whole will not be concentric, especially as in heavy jewels the hole is not in the exact centre of the stone, i.e., the hole is not concentric with the periphery, but the setting must be made so. The setting is now turned more down till it fits the small hole in the plate as far as the ledge, i.e., 3/32nd in., and the large punching the holes by turning up a plug to fit the hole, having a flange in which these equidistant holes are drilled at the correct distance; a centre punch can then be passed through the hole and the plate marked correctly for drilling. This also ensures the screws being arranged symmetrically in line. Great care is necessary in tapping a plate in. thick 10 B.A. or the tap will break; it is advis- able to use a drill rather larger than the standard size and slightly broach out the opposite end of the hole to that at which the tap is entered. If it is preferred the three screws which hold the setting can also be countersunk in the plate by making a small countersink, the pin of which fits the 10 B.A. hole. In this case the setting is made level with the plate and does not stand above it and a portion of the rim of the setting is cut away for half the diameter of the screw which is made to fit the countersink and turned down level with the plate. Care must be taken that the setting does not twist round, and it should be fixed when the countersink for the first screw is made and the screw put in before the others are made. 3 2 906
Fig. 4. Models showing Complete Jewel-hole Settings viewed inside and outside, with and without Endstones. end is then turned down till it fits the large hole in the plate. It is then removed from the faceplate and reversed, the end in which the jewel is set being cemented to the plate, run true, and the face turned down sufficiently for it to stand above the plate 1/32nd in., so that the heads of the screws which are to hold it in place may press against it. The hole in the brass may be turned out cone-shaped to within 1/16th in. of the edge, leaving a rim against which the screw heads press. The setting can be polished with tripole and pith or scratch brush and gilt. When all have been correctly fitted so that the end shakes of the arbor are correct, the plates must be tapped for the screws. There are three screws to each setting and they should be made from silver steel, hardened, tempered and polished, and blued. The threads should be small and the heads large to clamp the edge of the setting. Ten B.A. thread. with a rounded head. 3/16th in. diameter will be suitable. The plate should be drilled with a No. 55 drill at three equidistant points 1 mm. from the edge of the hole. If drilled too close when tapped the metal will be forced in and the setting will not fit. 1 It is advisable to make a templet for centre ! If endstones are required they are mounted in brass rims turned out in the lathe like the jewel holes and secured to the setting by three small screws or sunk in the setting and held by the same screws which hold the setting. To jewel pallets the anchor is made either in brass or soft steel fitted to the 'scape wheel, then the pads are slotted either by a milling cutter or file and the jewels made to shape, polished and secured in the graver by shellac. Notes on the Illustrations, Fig. 1 shows the outside of the front plate of a regulator (i.e., the equivalent of the motion plate of an ordinary long-case clock, but having no motion work), indicating the setting of jewel holes, which are numbered as follows: I the pallet arbor, 2 the 'scape arbor, 3 third wheel, 4, centre wheel, and 5 hour wheel, 2, 4 and 5 being lengthened pivots to take the seconds, minute and hour hand collets. No. 6, on a projecting bracket, takes the arbor of a jockey roller, which carries the weight line to the side of the case and which is jewelled. The pivot bush, marked x, is a metal hole for the winding arbor, which is not jewelled, being both to large, and subject to a heavily weighted 'live load. All the jewelling shown is duplicated on the other plate: Fig. 2, a series of ten scale sketches,
