The Boy Mechanic Part 38

** How to Make a Merry-Go-Round Swing [131]

A 6 by 6-in. piece of wood 12 ft. long is used for the center pole. Bore a 3/4-in. hole in each end to a depth of 6 in. Place a 3/4-in. bolt in each hole, the bolt being long enough to protrude 2 in. beyond the end of the wood. Short pieces of wood are nailed on the center pole about 2 ft. from the end that is to be used for the bottom. This should form a hub on which to place the inner ends of the extending spokes that hold the platform. The spokes are made from twelve pieces of 2 by 4-in. material 12 ft. long.

Usually a wheel can be found in a sc.r.a.p pile suitable to place on the pin that is in the top end of the center pole. The wheel should be open

[Ill.u.s.tration: Side and Top View]

or have spokes. This wheel is used to attach wires for guying. The bottom pin in the center pole is placed in a hole that is bored into a block of wood about 12-in. square and 3 or 4 in. thick. A piece of sheet metal should be drilled and placed on the pin between the block and end of the pole to make a smooth bearing.

The center pole is now placed in position and guyed with six wires that are about 35 ft. long. Stakes are driven into the ground and the wires fastened to them and to the wheel at the top end of the pole. Care should be taken when attaching the wires to get the center pole to stand perpendicular. Twelve hooks should be placed at equal distances around the center pole about 1 ft. from the top end. Wires are fastened to these hooks and to the twelve 2 by 4-in. pieces used for the spokes. The wires should be tied around each spoke about 2 ft. from the ends. s.p.a.ce the spokes with equal divisions and cover the outer 2 ft. of the ends with boards, as shown in the plan sketch on the right hand end of the drawing. The boards may be nailed or bolted. If bolted and the wires made in a loop at the hooks, the swing can easily be taken apart and changed from one place to another.

--Contributed by A. O. Graham, Fort Worth, Tex.

** Home-Made Arc Lamp [132]

The frame of the lamp is made from bar metal 3/4 in. wide and 1/8 in. thick, bent and welded to make a continuous loop in the shape as shown at G in the sketch. This frame should be about 10-1/2 in.

long with the upper or wider part 4 in. long, and the lower part 6-1/2 in. long. The width should be about 5-1/4 in. at

[Ill.u.s.tration: Arc Lamp]

the top and 4 in. at the bottom. A cross bar, L, made of the same material, is fitted into the off-set in the frame and riveted.

Holes are drilled through the frame and bra.s.s bus.h.i.+ngs, H and J, are fitted for bearings to receive the adjusting bra.s.s rod, B, which should be 1/4 in. in diameter. A bra.s.s curtain rod can be used for the rod B, and on its lower end a socket, P, is soldered.

A piece of bra.s.s 2 in. long, 1/2 in. wide and 1/8 in. thick is used for the armature, A, to be operated by the magnet coil, C.

The coil, C, is made in the usual manner by wrapping No. 14 cotton-covered magnet wire on a wooden spool that has a soft iron core. The spool is about 2-1/2 in. long. The armature, A, is drilled, making a hole just a little larger than the rod, B, and is adjusted in place by two set screws, D and E. A soft piece of iron, F, is fastened to the opposite end of the armature with a screw, which should be placed directly under the end of the coil's core. This end of the armature may be kept from swinging around by placing it between a U-shaped piece of bra.s.s fastened to the cross piece L. At the bottom end of the frame, and directly centering the holes H and J, a hole is drilled to receive a hard rubber bus.h.i.+ng, R, for insulating the bra.s.s ferrule, S, that holds the lower carbon.

One connection is made from the main to the upper binding-post, which is in turn connected to one terminal of the coil, C, the other coil terminal being attached to the frame. The other main connection is made to the lower binding-post, which is also connected to the bra.s.s ferrule, S, by soldering. The two binding-posts are insulated from the frame the same as the ferrule S. When using on a 110-volt circuit there must be some resistance in connection, which may be had by using German silver wire, or a water rheostat heretofore described.

--Contributed by Arthur D. Bradlev. Randolph, Ma.s.s.

** Irrigation [132]

The Mexican government has appropriated $25,000,000 for irrigation work.

** How to Hang Your Hat on a Lead Pencil [133]

Take a smooth hexagon lead pencil, one without either rubber or metal end, and place it against a door or window casing; then with a firm, heavy pressure slide the pencil some 3 or 4 in. and it will stay as if glued to the casing. You may now hang your hat on the end of the pencil.

When you slide the pencil along the casing, do it without any apparent effort, and it will appear to your audience as though you had hypnotized it. This is a very neat trick if performed right.

Figure 1 shows the pencil on the casing and Fig. 2 the hat hanging on it.

[Ill.u.s.tration: Pencil Trick]

** Tying a Knot for Footb.a.l.l.s [133]

One of the most prominent English football clubs kept the tying of this knot on the rubber hose of their football a secret and never allowed all of its members to know how it was tied. This tie can be used on grain sacks, and in numerous other like instances. Make one loop in the cord and then another exactly the same way, as

[Ill.u.s.tration: A Secure Knot]

shown in Fig. 1, placing the end of the cord under the first loop, then pulling at each end of the cord as in Fig. 2.--A.E.J.

** Stove polish [133]

Stove polish consists of 2 parts graphite, 4 parts copperas and 2 parts bone black, mixed with water to form a paste.

** How to Give an Electric Shock While Shaking Hands [133]

There is nothing quite so startling as to receive an electric shock unexpectedly and such a shock may be given to a friend while shaking hands upon meeting. The shock produced is not harmful and the apparatus can be carried in the pocket. It consists of a small induction coil that can be constructed at home.

The core of the coil, A, Fig. 1, is constructed in the usual manner, of small soft-iron wire to make a bundle about 3/16 in. in diameter and 2 in. long. The coil ends are made from cardboard, about 1 in. in diameter, with a 3/16-in. hole in the center. The hole

[Ill.u.s.tration: Details of Induction Coil]

should be cut as shown in Fig. 2, so as to have four small pieces that can be bent out, leaving the projections as shown. After wrapping three or four turns of paper around the bundle of wires the cardboard ends are put on with the projections inside, so the coils of wire will hold them in place. About 70 turns of No. 24 gauge double covered magnet wire is first placed on the core, for the primary, and then 1,500 turns of No. 32 or 34 gauge double-covered wire is wrapped on top of the primary, for the secondary. Sufficient length of wire must be left outside at each end of both windings to make connections. The vibrator B, Fig. 1, and the support C are made from thin spring steel, about 1/8 in.

wide, bent as shown and securely fastened to the cardboard end of the coil. The armature is made from a soft piece of iron, about 3/16 in. in diameter and 1/16 in. thick, which is soldered to the end of the vibrator directly opposite the end of the core. A small screw is fitted in the end of the support, C, for adjustment, which should be tipped with platinum and also a small piece of platinum placed where the screw will touch the vibrator, B.

One of the primary wires is connected to the screw support. The vibrator, is connected to a flash lamp battery, D. The other primary wire is connected to a switch, S, which in turn is connected to the other terminal of the battery. The switch, S, may be made from a 3/8-in. cork with the wires put through about 3/16 in. apart and allow them to project about 1/2 in. The plate E is cut about 1/2 in. square from a piece of copper and is fastened to the heel of one shoe and connected with a wire from the secondary coil which must be concealed inside of the trouser leg. The other secondary wire is connected through the coat sleeve to a finger ring, F. The vibrator screw must be properly adjusted. When the vibrator is not working the armature should be about 1/16 in. from the core and directly opposite.

The coil when complete will be about 2-1/2 in. long and 1 in. in diameter. The coil can be placed in an old box that has been used for talc.u.m powder or shaving stick. The s.p.a.ce around the coil in the box can be filled with paper to keep it tight.

The coil and battery are carried in the pockets and the cork b.u.t.ton put in the outside coat pocket, where it can be pressed without attracting attention.

** Experiment with Heat [134]

[Ill.u.s.tration: Heat Experiment]

Place a small piece of paper, lighted, in an ordinary water gla.s.s.

While the paper is burning turn the gla.s.s over and set into a saucer previously filled with water. The water will rapidly rise in the gla.s.s, as shown in the sketch.

** How to Attach a Combination Trunk Lock [134]

[Ill.u.s.tration: Trunk Lock]

A small combination lock for chests can be purchased for a small sum of money and attached to a trunk cover after first removing the old lock as shown in Fig. 1. It is necessary to add 1/2-in. to the thickness of the trunk lid or cover. This may be done by placing a bra.s.s plate 1/8-in. thick on the outside and a board 3/8-in. thick on the inside. The lock, bra.s.s plate, board and trunk cover are all securely riveted together. The support for the dial is soldered to the bra.s.s plate.