Part 8 (1/2)

The wire may be wound on by hand, but a winder (App. 93) will do much better and quicker work.

APPARATUS 84.

[Ill.u.s.tration: Fig. 58.]

[Ill.u.s.tration: Fig. 59.]

_113. Horseshoe Electro-Magnet._ Fig. 58. Bend soft iron wires, and make a bundle of them. If you wish to wind the wire around spools, the bundle cannot be very large. It will be found best to make the bundle about 3/8 in. in diameter, and not to use the spools. Strong paper should be wrapped once or twice around the legs of the horseshoe, and the insulated wire, say 4 layers, can then be wound directly upon this. (See -- 115 for method of making connection between the coils.) It is a little troublesome to wind wire upon a horseshoe like this, and for App. 85.

Spools are handier, because each can be wound separately, and then be slipped in place. The ends of the horseshoe should be filed smooth.

APPARATUS 85.

_114. Electro-Magnet._ Fig. 59. An ordinary iron staple is useful as the core of a small magnet. One like this is shown also in Fig. 94, used as a telegraph sounder. It takes some time to wind 4 layers of wire on to each leg of the staple, so be sure to see -- 115 about the method of winding. In Fig. 59 the half-hitches (-- 110) are not shown. Coat the finished coils with paraffine.

115. Method of Joining Coils. Fig. 60. If A and B represent the two cores of a horseshoe electro-magnet, the coils must be joined in such a manner that the current will pa.s.s around them in opposite directions, in order to make them unlike poles. The current is supposed to pa.s.s around B, Fig. 60, in the direction taken by clock hands, while it pa.s.ses around A in an anti-clockwise direction. The inside ends, -- 123, of the coils may be twisted together, or fastened under a screw-head. In Fig.

60 one coil is shown to be a continuation of the other.

[Ill.u.s.tration: Fig. 60.]

APPARATUS 86.

[Ill.u.s.tration: Fig. 61.]

[Ill.u.s.tration: Fig. 62.]

_116. Electro-Magnet._ Fig. 61. Wind 6 layers of No. 24 or 25 insulated copper wire around a 5/16 machine-bolt that is 2-1/2 in. long. Fig. 61 shows one method of holding the bolt solidly in an upright position, so that magnetic figures can be easily made and the magnet studied. Two nuts are used, the lower one being counter-sunk, so that the base will stand flat upon the table. This bolt is shown without washers (-- 119), and will do fairly well to show the action of electro-magnets. The ends of the wire should always be left 5 or 6 in. long, and be led out to binding-posts. The coil may be held in place, and its turns kept from untwisting by coating it with paraffine. The base may be of any desired size.

APPARATUS 87.

_117. Electro-Magnet Core._ Fig. 62. This shows another method of fastening a bolt-core in an upright position. This is done without the use of two nuts. A strip of tin, T, 1 in. wide, is punched and slipped onto the 5/16 bolt before the nut is screwed on and the coil wound. This is fastened to the base by screws, S. Washers, W, are here shown. (See -- 119 for washers.)

APPARATUS 88.

_118. Bolt Electro-Magnets_ are easy to make, according to the directions given, and they are, when finished, more like the regular purchased magnets than any of the other forms described. With proper batteries (App. 3, 4, etc.,) they can be used for a great variety of purposes, as will be seen. There are many forms of bolts in the market, but the ordinary ”machine bolt,” 5/16 in. in diameter, is best for our purposes. The ones 2 and 2-1/2 in. long are used.

119. Washers or coil ends are used on the bolt magnets so that considerable wire can be wound on closely and evenly. These are made out of thick pasteboard, which cuts smoother if it has been soaked in melted paraffine. Unless you know how, you will find it a hard job to make the hole in the exact center of the washer. The method of easily making washers is ill.u.s.trated in Fig. 63.

First place a spool (the end of which is 7/8 or 1 in. in diameter) upon the table, and lay the pasteboard upon this. Push a large round nail through the pasteboard into the hole in the spool. The nail should be nearly as large as the hole. Use the large nail as a handle, and with the shears cut around the edge of the spool end. Cut the washer as round as possible, and be careful not to cut into the spool.

The holes in the washers will be a little smaller than the 5/16 bolt.

This will make the washers hold tightly to the bolt when you force them on. Fig. 64 shows the bolt-core, with the washers in place. If you cannot get a large nail, a lead-pencil, or sharpened dowel, will do to force through the pasteboard.

[Ill.u.s.tration: Fig. 63.]

120. Insulation of Cores. While the covering on the wire would probably be all that is necessary to thoroughly insulate the coil from the core, it is better to wind a layer or two of paraffine paper around the bolt (Fig. 65) before winding.