The Boy Mechanic Part 18

[Ill.u.s.tration: Simple Telegraph Line]

the sounders is very high, the batteries do not run down for a long time.

--Contributed by A. D. Stoddard, Clay Center, Kan.

** How to Make a Thermo Battery [59]

A thermo battery, for producing electricity direct from heat, can be made of a wooden frame, A, with a number of nails, B, driven in the vertical piece and connected in series with heavy copper wires, C. The connections should all be soldered to give good results, as the voltage is

[Ill.u.s.tration: Thermo Battery]

very low and the resistance of an unsoldered joint would stop the current. The heat may be supplied by an alcohol lamp or other device, and the current may then be detected by means, of a simple galvanometer consisting of a square spool of No. 14 or No. 16 single-covered wire, E, with a pocket compa.s.s, F, placed on top.

Turn the spool in a north and south direction, or parallel with the compa.s.s needle. Then, when the nail heads are heated and the circuit completed, the needle will swing around it at right angles to the coils of wire. Applying ice or cold water to the nail heads will reverse the current.

--Contributed by A. C. A., Chicago.

** How to Discharge a Toy Cannon by Electricity [59]

A device for discharging a toy cannon by electricity can be easily made by using three or four dry batteries, a switch and a small induction coil

[Ill.u.s.tration: Electrical Attachment for Discharging Toy Cannon]

capable of giving a 1/8-in. spark. Fasten a piece of wood, A, to the cannon, by means of machine screws or, if there are no trunnions on the cannon, the wood may be made in the shape of a ring and slipped on over the muzzle. The fuse hole of the cannon is counterbored as shown and a small hole is drilled at one side to receive a small piece of copper wire, E. The wood screw, C, nearly touches E and is connected to one binding post of the induction coil. The other binding post is connected with the wood screw, D, which conducts the current into the cannon, and also holds the pieces of wood, A and B, in position.

When the cannon is loaded, a small quant.i.ty of powder is placed in the counterbore, and the spark between C and E ignites this and discharges the cannon. A cannon may be fired from a distance in this way, and as there is no danger of any spark remaining after the current is shut off, it is safer than the ordinary cannon which is fired by means of a fuse.

--Contributed by Henry Peck, Big Rapids, Mich.

** Simple Electric Lock [60]

The ill.u.s.tration shows an automatic lock operated by electricity, requiring a strong magnet, but no weights or strings, which greatly simplifies the device over many others of the kind.

[Ill.u.s.tration: Lock Operated by a Magnet]

The weight of the long arm, L, is just a trifle greater than the combined weights of the short arms, A and S. The fulcrum of the lever is at C, where there is a staple. The lever swings on one arm of the staple and the other arm is so placed that when the lever is in an upright position, with the long arm at L', it will not fall because of its greater weight but stays in the position shown. The purpose of this is to leave the short arm, A, when in position at A', within the reach of the magnet. Arm L rests on an L-shaped hook, H; in this position the door is locked.

To unlock the door, press the b.u.t.ton, B. The momentum acquired from the magnet by the short arms, A and S, is sufficient to move the long arm up to the position of L'. To lock the door, press the b.u.t.ton and the momentum acquired from the magnet by the short arms, now at A' and S', is sufficient to move the long arm down from L' to the position at L.

--Contributed by Benjamin Kubelsky, Chicago.

** Direct-Connected Reverse for Small Motors [60]

A simple reverse for small motors can be attached directly to the motor as shown in Fig. 1. Fig. 2 shows the construction of the reverse block: A is a strip of walnut 5/8 in. square and 3/8 in.

thick with strips of bra.s.s or copper (BB) attached as shown. Holes (CC) are drilled for the wire connections and they must be flush with the surface of the block. A hole for a 1/2 in. screw is bored in the block. In Fig. 1, D is a thin strip of walnut or other dense, hard wood fitted to the binding posts of the brush holders, to receive the screw in the center.

Before putting the reverse block on the motor, remove all the connections between the lower binding posts and the brush holders and connect both ends of the field coil to the lower posts. Bend the strips BB (Fig. 2) to the proper position to make a wiping contact with the nuts holding the strip of wood D, Fig. 1. Put the screw in tight

[Ill.u.s.tration: Direct-Connected Reverse]

enough to make the block turn a little hard. Connect as shown in the ill.u.s.tration. To reverse, turn the block so the strips change connections and the motor will do the rest.

--Contributed by Joseph B. Keil, Marion, Ohio.

** A Handy Ice Chisel [61]

Fis.h.i.+ng through the ice is great sport, but cutting the first holes preparatory to setting the lines is not always an easy task.

The ice chisel here described will be found very handy, and may be made at very slight expense.

In the top of an old ax-head drill a 9/16-in. hole, and then tap it for a 3/8-in. gas-pipe, about 18 in. long. Thread the other end of the pipe, and screw on

[Ill.u.s.tration: Combination Ax and Ice Chisel]

an old snow-shovel handle. When ready for use, screw the two pieces together and you have your chisel complete.

A short ax-handle may be included in the outfit. When the holes are finished and your lines set, unscrew the pipe from the head of the ax, put in the handle, and your ax is ready to cut the wood to keep your fire going.

--Contributed by C. J. Rand, West Somerville, Ma.s.s.

** More Uses for Pipe Fittings [61]

It would seem that the number of useful articles that can be made from pipes and fittings is unlimited. The sketch shows two more that may be added to the list. A and B are front and side views of a lamp-screen, and C is a dumbbell. The lamp shade is particularly useful for shading the eyes when reading or writing and, if enameled white on the concave side, makes an excellent reflector for drawing at night, or for microscopic work.

The standard and base, consisting of an ordinary pipe f.l.a.n.g.e bushed down to receive the upright nipple, are enameled a jet black, and if the device is to be used on a polished table, a piece of

[Ill.u.s.tration: Lamp Shade and Dumbbell]

felt should be glued to the bottom. A good way to hold the fan in the nipple is to use a small wedge.

The dumbbells are made of short pieces of 3/4-in. pipe with 1-2-in. couplings fastened to each end by pouring melted lead in the s.p.a.ce between the pipes and the couplings. The appearance is greatly improved by enameling black, and if desired the handles may be covered with leather.

--Contributed by C. E. Warren, M. D., North Easton, Ma.s.s.

** Sealing-Wax Bent While Cold [61]

If a piece of sealing-wax is supported in a horizontal position by one end, as shown at A in the sketch, it will gradually bend to the shape indicated by the dotted lines B. To attempt bending it with the hands would result in breaking it unless a steady pressure were applied for a long time. This peculiar property is also found in ice.

[Ill.u.s.tration: Bending Cold Sealing-Wax]

** Homemade Pottery Kiln [62]