[Figure 185] shows a detail of the boom. Cut the side sticks H 18 inches long, and fasten between them the separators I, which should be just long enough to allow clearance for the spool pulley J. The pulley is mounted on the axle K. Screw the lower ends of the boom to the mast, at a point 2½ inches above the base.
The Windlass for raising the derrick boom, and for hoisting the loads, is shown in detail in [Fig. 186]. Bore a hole through upright L for the axle M to stick through, and cut axle M enough smaller than the spool drums N so they will turn easily. Fasten a crank and handle to one end of each spool, and drive a brad through each end of the axle to prevent the drums from sliding off. Cut four notches in the inner flange of each spool, as shown, and pivot the catches O to the post L, in the positions indicated, so they may be thrown into the notches to lock the windlass ([Fig. 176]).
Fig. 186.—Detail of Derrick Windlass.
The Hoisting Cables should be made of strong cord. Fasten one end of the cable for raising the boom to a nail (P, [Fig. 176]), and run this cord up and over the mast pulley, then down through screw-eye G and over to one drum; tie it securely to the drum so it will not slip around. The other cable should be fastened between the nut and washer of the magnet, as shown in [Fig. 180], run up and over the boom pulley J, then through screw-eye G, and tied to the second drum.
[Figure 176] shows how the dry-cell may be strapped to the base board in front of the mast, and how the wires that connect the electro-magnet, switch, and cell should be twisted around the hoisting cable, part way, and the remainder of their length allowed to hang. Be sure to cut the wires long enough to reach from a table-top down to the floor. Use flexible wire if you can get it.
By mounting the base upon spool wheels, your derrick can be moved along a table-top. Spool-ends may be used for the wheels, and can either be screwed to the edge of the base, or be fastened upon axles as the wheels of the Electric Motor Truck are fastened ([Figs. 203] and [208]).
How the Derrick Works. It is probably unnecessary to explain that a load is picked up by throwing over the switch lever to the contact point and closing the circuit, and that it is dropped by throwing off the switch lever and opening the circuit—which causes the electro-magnet to lose its magnetism.
A Toy Shocking Machine..The little shocking machine shown in [Fig. 187] is a harmless toy with which you can have an endless amount of fun when entertaining friends. The shock it produces is not severe, but strong enough to make your friend's arm and wrist muscles twitch, and perhaps cause him to dance. Large shocking coils contract the muscles to such an extent that it is impossible to let go of the metal grips until the current has been shut off, but in our small shocking machine the handles can be dropped the instant the person holding them wishes to do so.