The Boy Mechanic, Book 2: 1000 Things for Boys to Do

by Unknown

A Small Shocking Machine

The Shocking Coil as It is Used for Amusement, or in the Manner a Current is Given a Patient

An amusing as well as instructive shocking machine, usually called a medical coil, can be easily constructed from a discarded buzzer or electric bell, four binding posts, some pieces of insulated wire, two carbon rods, and a rheostat.

The Base upon Which the Buzzer and Rheostat are Fastened, and the Electrical Connections (Fig. 1, Fig. 2)

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.