The core for holding the cylindrical wax records is 4-1/2 in. long and made of wood, turned a little tapering, the diameter at the small or outer end being 1-5/8 in., and at the larger end, 1-7/8 in. A wood wheel with a V-shaped groove on its edge is nailed to the larger end of the cylinder. The hole in the core is fitted with a brass tube, driven in tightly to serve as a bearing. A rod that will fit the brass tube, not too tightly, but which will not wobble loose, is threaded and turned into the upper end of the support. The core with its attached driving wheel is shown in Fig. 3. The dotted lines show the brass bearing and rod axle. The end of the axle should be provided with a thread over which a washer and nut are placed, to keep the core from coming off in turning.
The sound box, Fig. 2, is about 2-1/2 in. in diameter and 1 in. thick, made of heavy tin. The diaphragm, which should be of thin ferrotype tin, should be soldered to the box. The needle is made of a piece of sewing needle, about 1/8s in. long, and soldered to the center of the diaphragm. The first point should be ground blunt, as shown in the sketch. When soldering these parts together, take care to have the diaphragm lie perfectly flat and not made warping by any pressure applied while the solder is cooling.
The tin horn can be easily made, attached to the sound box with a piece of rubber hose and held so it will swing the length of the record by a rod attached to the top of the box, as shown. The motor can be controlled by a small three or four-point battery rheostat.
Contributed by Herbert Hahn, Chicago, Ill.
A Substitute for a Compass
Pencil on the Knife Blade
An easy way to make a pencil compass when one is not at hand, is to take a knife with two blades at one end, open one to the full extent and the other only halfway. Stick the point end of the fully open blade into the side of a lead pencil and use the half-open blade as the center leg of the compass. Turn with the knife handle to make the circle.
Contributed by E. E. Gold. Jr., Victor, Colo.