It is first necessary to determine the diameters of the disks. If the center distances between all the holes were equal, the diameters would, of course, equal this dimension. When, however, the distances between the centers are unequal, the diameters may be found as follows: Subtract, say, dimension y from x, thus obtaining the difference between the radii of disks C and A ([see right-hand sketch]); add this difference to dimension z, and the result will be the diameter of disk A. Dividing this diameter by 2 gives the radius, which, subtracted from center distance x equals the radius of B; similarly the radius of B subtracted from dimension y equals the radius of C.
For example, 0.930-0.720 = 0.210 or the difference between the radii of disks C and A. Then the diameter of A = 0.210 + 0.860 = 1.070 inch, and the radius equals 1.070 ÷ 2 = 0.535 inch. The radius of B = 0.930-0.535 = 0.395 inch and 0.395 × 2 = 0.790, or the diameter of B. The center distance 0.720-0.395 = 0.325, which is the radius of C; 0.325 × 2 = 0.650 or the diameter of C.
Fig. 5. Flange Templet with Buttons Attached
Fig. 6. Hinge Jig Templet with Buttons Attached
After determining the diameters, the disks should be turned nearly to size and finished, preferably in a bench lathe. First insert a solder chuck in the spindle, face it perfectly true, and attach the disk by a few drops of solder, being careful to hold the work firmly against the chuck while soldering. Face the outer side and cut a sharp V-center in it; then grind the periphery to the required diameter. Next fasten the finished disks onto the work in their correct locations with their peripheries in contact, and then set one of the disks exactly central with the lathe spindle by applying a test indicator to the center in the disk. After removing the disk and boring the hole, the work is located for boring the other holes in the same manner.
Fig. 7. Hinge Jig Templet Illustrated in [Fig. 6]
Small disks may be secured to the work by means of jeweler’s wax. This is composed of common rosin and plaster of paris and is made as follows: Heat the rosin in a vessel until it flows freely, and then add plaster of paris and keep stirring the mixture. Care should be taken not to make the mixture too stiff. When it appears to have the proper consistency, pour some of it onto a slate or marble slab and allow it to cool; then insert the point of a knife under the flattened cake thus formed and try to pry it off. If it springs off with a slight metallic ring, the proportions are right, but if it is gummy and ductile, there is too much rosin. On the other hand, if it is too brittle and crumbles, this indicates that there is too much plaster of paris. The wax should be warmed before using. A mixture of beeswax and shellac, or beeswax and rosin in about equal proportions, is also used for holding disks in place. When the latter are fairly large, it may be advisable to secure them with small screws, provided the screw holes are not objectionable.