Fig. 32.
Fig. 33.
Let us see how this rule will work in repairs. Suppose we have a clock brought in with the pallet fork missing, and that the movement is one of those in which the pallet arbor is held by adjustable cocks which have been misplaced or lost, so that we don’t know the center distance of the pallet arbor and escape wheel. We shall have to make a new part.
Measure the escape wheel, getting its diameter carefully, take half of this as a radius, and mark out the circle with a fine needle point on some copper, brass or sheet steel, drawing the escapement as detailed in Figs. [30] and [32]. Then measure carefully the angles made by the tangents with the center line; take the steel which is to be used in making the pallets and fork; draw on it a center line; lay off the tangents and the lift lines; draw the locking arcs and the lifting planes carefully from the tangents and give the rest of the fork a symmetrical shape. Use needle points to draw with and have your protractor large enough to measure your angles accurately. Then drill or saw out and file to your lines, except on the locking and lifting planes; leave these large enough to stand grinding or polishing after hardening. Harden; draw to a straw color and polish the planes. Your verge will fit if it has not warped in hardening. If this is the case, soften the center, keeping the heat away from the pallets, and bend or twist the arms until the verge will fit the drawing, when laid on top of it. In grinding the pallets the fork should be mounted on its arbor and the latter held between the centers of a rounding-up tool while the grinding is done by a lap in the lathe. This insures that the planes will be parallel to the pallet arbor and hence square with the escape wheel teeth, so that they will not create an end thrust on either escape or pallet arbor. It is also the quickest, easiest and most reliable way of doing the job. When clocks come in with the pallets badly cut; soften the center of the fork, place the ends between the jaws of a vise, squeeze enough to bring them closer, mount in the rounding-up tool and lap off the cut planes until they are smooth and stand at the proper angle; then polish. This is done quickly.