Next you can mount a lap in place of the saw and smooth the fronts and backs of the teeth and if you have a rather thick disc the outer edge of the rim, between the teeth, may also be smoothed.
If you have a good strong pivot polisher, mount a triangular end mill in the spindle, lock the yoke, and cut the arcs of circles of the hub and rim from edge to edge of the spokes, feeding carefully against the mill with the hand on the lathe pulley.
Put on your jeweling tailstock and open the wheel to fit the pinion, collet, or arbor, if there is no collet.
You now have the wheel all done, except facing the side that was soldered to the cement brass and trimming up the corners of the spokes at the rim and hub, and you have got it round, true and correct in much less time than you could have done in any other way, while an immense amount of work with the file and eye-glass has been avoided. It is true because it was soldered in position at the beginning and has not been removed until finished.
Sometimes what are known from their appearance as club-shaped teeth are used in the wheels of Graham’s escapements. Pendulums receive their impulse from escapements made in this manner partly from the lifting planes on the pallets, and partly from the planes on the scape wheel. The advantage gained by this method is, that wheels made in this way will work with the least possible drop, and consequently, power is saved; but the power saved is thrown away again in the increased friction of the planes of the wheel against those of the pallets, which is considerably more than when plain-pointed teeth are used on the escape wheel.
Clock pallets are usually made of steel, and on the finer classes of work jewels are often set into them to prevent the oil from drying, after the same fashion as jewels are placed in steel pallets in a lever watch; but it is obvious that stone pallets made in this way have to be finished with polishers held in the hand, and that, except in factories, they cannot be made so perfectly regular, especially that pallet that is struck downwards, as the particular action of a fine Graham escapement requires. When great accuracy is required, the pallets are usually made of separate pieces, and the acting circles ground and polished on laps, running in a lathe. This method of constructing pallets also allows a means of adjustment which in some particular instances is very convenient.
There is also a plan of making jeweled pallets adjustable, which is practiced on fine work, such as astronomical and master clocks. The pallet fork consists of two pieces of thin, hard, sheet brass, cut out in the usual form and two mounted on one arbor. Circular grooves are cut in the sides of both plates, at the proper distance, and of the proper size to receive the jewels which are the acting parts of the pallets. When jewels cannot be made of the desired size, pallets of steel are made, and the jewels are then set into the steel large enough for the teeth of the wheel to act upon. The two parts of the fork are fastened at a given distance apart, and the jewels, or pieces of steel, go in between them, and, after they have been adjusted to the proper position, are fastened by screws that pull the frames close together and press against the edges of the jewels. Pallets made in this manner have a very elegant appearance. Another method is to have only one frame, and to have it thick enough, where the jewels have to be set in, to allow a groove to be cut in its side as deep as the jewels (or the pieces of steel that hold the jewels) are broad, and which are held in their proper position by screws. This system of jeweling pallets is frequently adopted by the makers of fine mantel clocks.
Fig. 37. Brocot’s visible escapement, escaping over
120° with pointed teeth. Dotted lines on pallets
show where they are cut to avoid stopping.