Clean and dry both of the glass plates very carefully and then give them each two thin coats of white shellac. After they have been dried, lay one of the plates on the paper pattern so that the outside of the plate will coincide with the largest circle on the paper.
Then place a weight in the center of the plate so that it will not move, and stick sixteen of the tinfoil sectors on the plate with thick shellac. The sectors are arranged symmetrically on the plate, using the eight-inch and sixteen-inch circles and the radial lines as guides. Both plates should be treated in this manner. Each sector should be carefully pressed down on the glass, so that it will stick smoothly without air-bubbles or creases. When all the sectors are in place the plates will appear like that shown in Figure 35.
The Bosses will have to be turned out at a wood-working mill or at some place where they have a turning-lathe. The bosses are four inches in diameter at the large end and one inch and one-half at the other. A groove is turned near the small end of each to accommodate a round leather belt.
A hole should be made in each boss about half-way through from the small end. These holes should be bushed with a piece of brass tubing having an inside diameter of one-half inch. The tubing should go into the hole very snugly and be a "driven fit."
Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.
The bosses should both be given a coat of shellac, and after this is dry, fastened to the glass plates on the same side to which the tinfoil sectors are attached. The best plan is to lay the disks on the paper pattern and adjust them until the outer edge coincides with the largest circle.
Then apply some bichromate glue to the flat surface of one of the bosses and place the latter in the center of the plate in line with the smallest circle.
Place a weight on the boss to hold it down firmly against the plate and leave it over night, or for ten or twelve hours, until thoroughly dry.
The glue is prepared by placing some high-grade glue in a tin cup and covering it with cold water. Allow it to stand until the glue absorbs all the water it will and becomes soft. Then pour the water off and add enough glacial acetic acid to cover the glue.