The Rheostat That is Used to Regulate the Flow of Current in the Carbon Hand Pieces (Fig. 3)
A base for attaching the parts is made of a piece of poplar, 10 in. long, 5 in. wide, and 1/2 in. thick, which can be finished as desired, but a good method is to shape the edge like molding and give it a mahogany stain, and when dry apply a coat of white shellac, which should be allowed to dry a day, whereupon the surface is rubbed with prepared wax. When the base is ready, mount the buzzer at one end. This can be easily done by making an L-shaped piece of metal, A, which is fastened to the base with a screw, and to the yoke of the magnet coil with a small bolt. If the armature and its connections are also used from the buzzer, the height of the coils must be taken in consideration. These parts are fastened in position as shown, using an L-shaped piece of metal, B, for the spring end. The screw holding the armature spring to the base, as well as the vibrator screw, should be of such a length that it will enter the base far enough to permit a connection for a wire in a countersunk hole bored in the base from the under side. Binding posts are placed in the corners of the base in holes countersunk from the under side for the screw heads.
The rheostat is of the miniature-battery type, which has a round base and a coil of resistance wire with a lever passing over the coil. Such a rheostat can be purchased from an electrical store, but if the person constructing the shocking machine desires to make one, it is not difficult if a lathe is at hand.
To make the rheostat, turn up a disk, about 3 in. in diameter, from a piece of hard wood, such as oak, maple, or walnut, and form a circular groove in the upper surface, about 3/8 in. inside of the circumference. The groove is to admit a circular coil of resistance wire, and in making it, be sure to have it the proper size to take the coil snugly. The coil can be of any size, and to make it, resistance wire is wound around a piece of wire used as a mandrel. If the coil is 1/4 in., or a trifle smaller, in diameter, it will make a good size. Be sure that the depth of the groove is such that it will allow a part of the coils of the resistance wire to project above the surface of the wood disk. The coil of wire should be just long enough to fit in the groove and allow a 1-in. space between the ends, one of which is anchored to the base, at C, the other being attached to the binding post D. Drill a hole through the center of the disk and fasten a lever, taken from a switch, or one made of a piece of sheet brass, that will extend from the center to the outside of the disk, or over the resistance-wire coil. A small handle is attached to the outer end. A connection is made from the center support of the lever to the binding post E.
The connections for the buzzer and rheostat are made on the under side of the base, where grooves are cut to run the wires in, so that they will be below the surface of the wood. In the diagram, the binding post F is connected to the binding post D of the rheostat, which in turn is connected to the screw of the make-and-break point G. The other binding post H is connected to the bracket B supporting the armature spring. The binding post E of the rheostat is connected to the base binding post J. The magnet coils are connected, as shown, from K to L, and from M to B.
The two pieces of carbon, which are used for the hand pieces, are connected with silk-insulated wire. These connections are made to the binding posts F and H. The other two binding posts, J and L, are connected to a battery. The carbons used may be purchased, or taken from an old battery. Two or more dry cells are used for the current. The rheostat controls the amount of current passing through the hand pieces.—Contributed by Gilbert Crossley, Erie, Pa.
Secret Compartment in Ordinary Table Drawer
It is frequently desired to have some handy place for storing valuables where there is but little chance of discovering them. Secret drawers in tables usually require special and expensive changes, but with only a few simple changes on a regular drawer of any ordinary table, a secret compartment can be made which is as secure as can ordinarily be figured on, outside of a steel safe. Having chosen the desired table, a partition should be placed across the entire back part of the drawer, allowing for necessary space in the secret compartment. This partition should resemble the real back of the drawer as closely as it is possible to make it. The compartment must not be too wide, for the resulting small width of the front part of the drawer might then arouse suspicion. On the lower side of the secret compartment a strip of wood, A, should be attached with a screw, as shown in Fig. 1, allowing sufficient looseness so the strip may be turned end for end when necessary. With the strip set as shown, it will strike the front side B of the table when the drawer is pulled out, leaving the secret compartment still hidden. In order to expose this, it will be necessary to turn the strip, as shown in Fig. 2, when the drawer can be pulled out to its full length.
