The Boy Mechanic Part 23

[Ill.u.s.tration: KEY-A. wood; B. bra.s.s or iron soldered to nail; C.

bra.s.s; D. bra.s.s: E. wood: F. connection of D to nail; HH. binding posts]

** How to Make a Music Cabinet [77]

A neat music cabinet can be made as shown in the accompanying sketch. Each side, AA, Fig. 1, is cut from a board about 36 in. in length and 16 in. wide. Both are alike and can be cut from the same pattern. As the front legs curve out a little the main body of the boards AA should be 15 in. wide. The back, B, should be about 22 in. long by 16 in. wide and set in between sides AA. Cut the top, C, 16 in. long and 14-1/2 in. wide. The bottom must be the same length as the top and 13-1/2 in. wide.

The door, D, can be made panel as shown, or a single piece, 16 in.

wide and about 20 in. long. All material used is to be made from boards that will dress to 3/4 in. thick.

[Ill.u.s.tration: How to Make a Music Cabinet]

Shelving may be put in as shown in Fig. 2 and made from 1/4-in.

material. Make 12 cleats, E, 13-1/2 in. long, from a strip of wood 1/2 by 3/4 in., with a groove 1/4 by 1/4 in. cut in them. Fasten 6 cleats evenly s.p.a.ced on the inside of each of the sides, AA, with 3/4-in. brads. This will give seven s.p.a.ces for music and as the shelves are removable two places can be made into one.

** Easily Made Wireless Coherer [77]

A good wireless coherer may be made with very little expense, the only materials necessary being a gla.s.s tube, two corks: a magnetized needle and a quant.i.ty of iron and silver filings. Push a piece of wire through one cork and place in the bottom of the tube, as shown in the sketch.

Pour in the filings and insert the top cork with the needle pushed through

[Ill.u.s.tration: Detail of Coherer]

from above. The point of the needle should barely touch the filings and by slightly agitating the tube the iron filings will separate from the silver and cling to the magnetized needle, as shown.

In operation, the device must stand on end and should be connected in the circuit as shown in the sketch. When the electrical waves strike the needle, the conductivity of the filings is established and a click is heard in the receiver.

--Contributed by Carl Formhals, Garfield, Ill.

** One-Wire Telegraph Line [78]

The accompanying wiring diagram shows a telegraph system that requires no switches and may be operated with open-circuit batteries on a one-wire

[Ill.u.s.tration: Diagram of One-Wire Line]

line with ground connections at each end. Any telegraph set in which the key makes double contact can be connected up in this way.

--Contributed by R. A. Brown, Fairport, N. Y.

** How to Make a Water Rheostat [78]

A water rheostat may be made by fitting a bra.s.s tube with a cork, through which a piece of wire is pa.s.sed. The bra.s.s tube may be an old bicycle hand pump, A (see sketch), filled with water. Pushing the wire, B, down into the water increases the surface in contact, and thus decreases the resistance. An apparatus of this kind is suitable for regulating the current from an induction coil, when the coil is not provided with a regulator, and by using a piece of pipe instead of the tube, it can be used to regulate the speed of a motor.

When the pipe is used, a piece of bra.s.s or copper rod should be subst.i.tuted for the wire, in order to increase the surface. Adding salt to the water will decrease the resistance, and, when used with a motor, will give a greater speed.

--Contributed by John Koehler, Ridgewood, N. J.

[Ill.u.s.tration: Diagram of One-Wire Line Water Rheostat]

** Electric Door-Opener [78]

A very convenient and efficient device for unlocking any door fitted with a spring lock is shown in the accompanying sketches. A fairly stiff spring, A, is connected by a flexible wire cord to the k.n.o.b B. The cord is also fastened to a lever, C, which is pivoted at D and is released by a magnetic trigger, E, made from the armature and magnet of an old electric bell.

When the circuit is completed by means of a secret contact device outside the door, the magnet, F, pulls down the armature, which releases the trigger and allows the spring to open the lock. If there are metal numbers on the outside of the door they may be used for the secret contact, if desired,

[Ill.u.s.tration: Apparatus Placed on Inside of Door]

but if there are no numbers on the door, a small contact-board may be constructed by driving about 12 bra.s.s headed tacks into a thin piece of wood and making connections at the back as shown in the wiring diagram.

In this particular diagram the tacks numbered 1 and 7 are used for unlocking the door, the others being connected with the electric-bell circuit as indicated, for the purpose of giving an alarm should anybody try to experiment with the secret contacts.

By means of a pocket knife or other metal article the operator can let himself in at any time by connecting the tacks numbered 1 and 7, while a person not knowing the combination would be liable to sound the alarm. Of course, the builder of this device may choose a combination of his own and may thus prevent anybody else from entering the door, even those who read this description.

--Contributed by Perry A. Borden, Gachville, N. B.

[Ill.u.s.tration: Wiring Diagram]

** How to Tighten a Curtain-Roller Spring [79]

A common table fork can be used to hold the little projection on the end of a curtain roller for tightening the spring. Hold the fork firmly with one hand while turning the roller with the other.

Do not let go of the fork until the little catches are set in position to prevent the spring from turning, or else the fork may be thrown off with dangerous force.

** Alarm Clock Chicken Feeder [79]

An automatic poultry feeder, which will discharge the necessary amount of corn or other feed at any desired time, may be made by using an alarm clock as shown in the sketch. A small wire trigger rests on the winding key and supports the swinging bottom of the food hopper by means of a piece of string which connects the two.

When the alarm goes off the trigger drops and allows the door to open, thus discharging the contents of the hopper.

After the device has been in operation for some time the hens will run to the feeder whenever the. bell rings.

--Contributed by Dr. H. A. Dobson, Washington, D. C.

[Ill.u.s.tration: Will Open or Close Circuit as Desired]

** Homemade Disk-Record Cabinet [79]

Select some boards that have a nice grain and about 1 in. thick and 12-in. wide. Cut the end pieces each 36-in. long and trim down the edges so as to make them 11-3/8 in. wide. The top board is made 28-in. long and full 12-in. wide. The three shelves are cut 25-in. long and the edges trimmed so they will be 11-3/8 in. wide.

The distance between the bottom of the top board and the top of the first shelf should be 3 in. Two drawers are fitted in this s.p.a.ce, as shown in Fig. 1. A series of grooves are cut 1/4 in.

wide,