How Two Boys Made Their Own Electrical Apparatus Part 7

APPARATUS 73.

_99. Yoke._ Fig. 47. The yoke, Y, is a part of a carriage. This can be bought at a blacksmith's. The holes are already in, but it may require some filing before the nuts of the bolt magnets will fit down firmly.

[Ill.u.s.tration: Fig. 47.]

APPARATUS 74.

_100. Tin Armatures_ may be made by bending together 5 or 6 thicknesses of tin. Different forms of tin armatures are shown under telegraph sounders; these should have a hole punched at the center; through this is put a screw. The length of the armature will depend upon the distance the magnets are placed apart; they should be about 3/4 in. wide.

APPARATUS 75.

_101. Nail Armatures._ Fig. 48. A nail, N, placed through a piece of wood, A, will serve as a very simple armature. To make it a little heavier, if necessary, a piece of annealed iron wire, W, may be wound around N. Care should be taken to have the two parts fairly alike in size and weight.

[Ill.u.s.tration: Fig. 48.]

APPARATUS 76.

_102. Wire Armatures._ Fig. 49. Annealed iron wires make good armatures.

The short lengths of wire should be straightened (See App. 28) before binding them into a bundle. They may be held together with thread or paraffine, until they are in place, as, for example, in a wooden piece, A, Fig. 49. The bundle of wires should fit snugly into the hole made through A, and the wires should be bound together at each end with wire.

[Ill.u.s.tration: Fig. 49.]

APPARATUS 77.

_103. Trembling Armature._ Fig. 50. Armatures to be used upon electric bells, automatic current interrupters, buzzers, etc., may be called trembling armatures. They may be made entirely of sheet-tin. The part, F, which gives it the spring, should be about 5/8 in. wide. Its length will depend upon the particular apparatus to be made. It is made of 2 thicknesses of thin tin. See Fig. 50 for dimensions. The part N projects beyond L. This may be used to tap against a regulating screw, or to fasten a hammer on for an electric bell. The part, L, should have about 4 layers of tin on each side of F, and it should pinch F tightly.

[Ill.u.s.tration: Fig. 50.]

APPARATUS 78.

_104. Trembling Armature._ Fig. 51. When very rapid motions are desired in a trembling armature, App. 77 will be a little heavy. A light and quick-acting armature can be made of sheet-tin. The exact dimensions will depend upon the use to be made of it, but you will find the following a guide. Cut the part, B, E, out of thin tin. The covers and bottoms of tin cans are thinner than their bodies. The narrow part, B, should be about 1/4 in. wide and 2 in. long for a small apparatus, while E may be 3/4 in. square. Through E is a screw, which holds it firmly to a wooden piece, D, about 3/4 in. square. The part, E, can be made longer than its width, so that two screws can be used; this will keep A from jarring up or down.

[Ill.u.s.tration: Fig. 51.]

APPARATUS 79.

[Ill.u.s.tration: Fig. 52.]

_105. To File Thin Metal Strips._ Fig. 52. When sheet-metal is punched by the methods usually employed by boys, a bulge or bur is made on the underside around the hole. If this bur be hammered to flatten it, the hole is distorted and made smaller. It is better to file the bur down, at least part way. It is not convenient to file a piece of thin metal when it is held in a vise. It is better to use either a metal or a wooden clamp, as shown in Fig. 52; then the filing can be quickly and easily done. Y is the yoke to be filed. It is well to place a piece of metal, I, between the table and the end of the screw.

APPARATUS 80.

_106. Clamp._ Fig. 53. If you have no clamp to hold metal strips while filing them, you can put a screw, S, through one hole to hold the strip down fairly tight. Drive a nail, N, behind the strip. This will keep it from turning while you file the free end.

[Ill.u.s.tration: Fig. 53.]

_Electro-Magnetic Armatures._ A description of this form of armature is given in the chapter on electric motors. (See Index.)

CHAPTER IX.

ELECTRO-MAGNETS.

_107. Electro-Magnets_ are absolutely necessary in the construction of most pieces of electrical apparatus. There are several ways of making them at home. To quickly make a good-looking one, a winder (App. 93) is required. We shall divide our electro-magnets into four parts: Core, washers, insulation, and coil.

Of course, you know that when a current of electricity pa.s.ses through a wire, a magnetic field is produced around the wire. A coil of wire, or helix, has a stronger field than a straight wire carrying the same current, because each turn or convolution adds its field to that of the other turns. By having the center of the helix made of iron, instead of air, wood, or other non-magnetic bodies, the strength of the magnet is greatly increased. This central core may be fixed permanently in the coil, or be removable. For our purposes fixed cores are just as good as movable ones, and the coils are easily wound upon them.

When wire is wound by hand from a spool into a coil, or around a core, it soon becomes twisted and tangled. Make a winder. This will keep the wire straight and save much time.

APPARATUS 81.

[Ill.u.s.tration: Fig. 54.]

_108. Electro-Magnet._ Fig. 54. Drive a nail into a board so that it will project about 3/4 of an inch. A soft, or wrought-iron, nail is best, but a short, thick wire-nail will do. If you do not have a thick nail, use an iron screw. Wind 3 or 4 layers of insulated copper wire around it, and fasten the bare ends of the wire down with bent pins.

Number 24 wire will be found a good size for experimental purposes.

Touch the wires leading from the battery to the ends of the coil, and see if the nail will lift pieces of iron.

109. Note. Always leave at least 6 in. of wire at the ends of all coils and windings. This is needed for connections and repairs, as the wire is liable to get broken at any time around the binding-posts.

110. Note. After you have wound wire upon a core or spool, keep it from untwisting by taking a loop or hitch around it with the wire. Fig. 55 shows how this is done. Pull the end of the wire enough to make the loop stay in place.

APPARATUS 82.

_111. Electro-Magnet._ Fig. 56. Cut annealed iron wire into pieces, 3 inches long, straighten them (App. 28), and tie them with thread into a bundle about 5/16 in. in diameter. Melted paraffine run in between the wires will hold them in together, but stout thread will do. Wind 3 or 5 layers of No. 24 insulated copper wire upon the soft iron core. This is useful for simple experiments, and this idea may be applied to magnets to be used in pieces of apparatus. Hold the bundle of wires in a vise, and file the ends smooth, before winding on the wire. Paraffine should be used to hold the turns of insulated wire together.

[Ill.u.s.tration: Fig. 55.]

[Ill.u.s.tration: Fig. 56.]

[Ill.u.s.tration: Fig. 57.]

APPARATUS 83.

_112. Electro-Magnet._ Fig. 57. An electro-magnet with a removable core may be made by winding the wire on a spool. The core is made, as in App. 82, of soft iron wires, bound together with stout thread. A bolt may be used instead of the wire, but the wire loses its magnetism much quicker than a soft steel bolt would. (Study residual magnetism.) This magnet is strong enough for many purposes, but the wire is too far from the core, on account of the thickness of the wood, to make it efficient.