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.
[Ill.u.s.tration: Fig. 64.]
[Ill.u.s.tration: Fig. 65.]
[Ill.u.s.tration: Fig. 65-1/2.]
121. The Coils of wire to be used upon the bolt-cores should be put on with the winder (App. 93). For all ordinary purposes No. 24 or 25 single or double cotton covered copper wire will do. It is better to put on an even number of layers. The winding (See Fig. 70) begins at the nut-end of the bolt, and by using 6 or 8 layers of wire, instead of 5 or 7, both coil ends will be at the same end of the bolt.
122. Method of Winding the Coils. The winders used for bolt magnets are described in App. 91, etc. We shall suppose that the washer, W, Fig. 70, and the insulation, I, are upon the bolt before s.c.r.e.w.i.n.g it into the winder-nut, W N. Make a pinhole, P H, in the right-hand washer, as near the bolt-nut, B N, as possible. Stick about 6 in. of the wire through P H, and wind this end around W N, as shown, to hold the wire. The supply of wire should be upon a spool slipped onto some stationary rod (App.
23), so that you can give your entire attention to winding. Begin to turn the winder slowly at first. Turn the handle towards you when it is at the bottom, as in Fig. 70; that is, if you look at it from the side, turn the handle clockwise. Let the wire slip through your left hand as the turns are made, and guide it so that the turns will be close together. If they go on crooked, unwind at once, then rewind properly.
You can guide the wire best by holding your left hand about 8 or 10 inches from the bolt. As soon as you reach the left side or head end of the bolt, feed the wire towards the right. If at any time the layers become rough on account of one turn slipping down between turns of the previous layer, fasten a piece of paraffine paper around the coil as soon as the imperfect layer is completed. Wind on 8 layers, and count the number of turns in one or two of them, so that you can tell about how many turns in all you have around the core. Make a "half-hitch" (see -- 110) with the wire when the last layer is finished, to keep it from unwinding, and leave a 6 in. end.
The coil should be protected by fastening around it a piece of dark-colored stiff paper. Paraffine paper is good for this purpose. With a little practice you will be able to rapidly and neatly wind on the wire. The winder-nut, W N, must hold the bolt solidly to keep it from wobbling.
123. We shall call the starting end of the wire which pa.s.ses through P H, the inside end, and the end of the last layer the outside end. This can pa.s.s out between the washer and the paper covering.
APPARATUS 89.
_124. Experimental Horseshoe Electro-Magnet._ Fig. 66. Among the most useful pieces of apparatus for home use, is a good horseshoe electro-magnet. Fig. 66 shows a very convenient and practical form. With this, alone, can be shown all the principles of telegraph sounders, electric bells, etc. They are excellent for making magnetic figures (See text-book). You are supposed to be looking down on the App. in Fig. 66.
The bolts are 2 in. apart center to center.
[Ill.u.s.tration: Fig. 66.]
The bolt magnets are fully described in App. 88; the binding-posts, as App. 46; the yoke, as App. 71; the method of fastening to the base, as App. 90; the base is 5 4 7/8 in.; the magnets are made of 5/16 bolts, 2-1/2 in. long.
125. To Join the Coils, fasten the two inside ends (--123) of the wire to a middle binding-post, and carry the outside ends to the two outside binding-posts. In this way you can use either magnet alone, if desired (See experiments in text-book), or change the polarity at will by changing the connections. (See -- 115 and 123.)
APPARATUS 90.
_126. Fastenings for Electro-Magnet._ Fig. 67. When both electro-magnets are to be permanently fastened to a base, especially if tin yokes are to be used, as in App. 89, it is best to use a nut on each side of the yoke. It is important to have a perfectly tight connection between bolt and yoke. Several ways of fastening the bolts and yokes are shown; but it will be found best to cut holes in the base for the lower nuts, and to screw the yoke directly to the base. This makes a solid and pleasing arrangement. For the experimental magnets (App. 89) make the yoke 3-1/4 in. long, and place the magnets 2 in. apart center to center.
[Ill.u.s.tration: Fig. 67.]
CHAPTER X.
WIRE WINDING APPARATUS.
APPARATUS 91.
_127. Winder._ Fig. 68. In case you do not have any means of making a smooth hole for the "bearings" of the winders of App. 93 and 94, you can use a spool for the purpose. B is the end of a piece of board about 1 in. thick, 3 in. wide, and 6 in. long. The spool, A, is laid upon this, a band of tin, T, being used to hold it down firmly upon the end of B.
Screws, S, hold T down. A stove-bolt axle (See App. 93) is shown, and by using a nut, as explained, bolt magnets may be wound. By using the handle of App. 92, this arrangement can be used to wind almost anything, when used together with the attachment of App. 95.