94. Yokes are used to fasten two straight electro-magnets together to form a horseshoe electro-magnet. The reasons for using them should be understood. Soft iron should be used for yokes and armatures, as this is the best conductor of lines of magnetic force. Sheet-tin is made of thin iron, which is coated with tin. (Try a magnet upon a tin can.) This soft iron is very easily handled, bent, and punched, and is very useful for many purposes. The tin from old tomato cans, cracker boxes, etc., is just as good as any. The method of making your yokes will depend entirely upon the tools at your command. Several ways are given. Y, Fig. 47, shows the position of the yoke.
95. Yoke. For the experimental magnets ([App. 89]) a fairly large yoke is required in order to have the magnets far enough apart. If you have only a nail punch ([App. 26]) with which to make holes in tin, you will be obliged to punch but one thickness at a time. (See method of punching sheet-metal, [App. 26].) Cut 5 or 6 pieces of the tin, 3¼ × 1 in. With a center punch (tools) or sharp-pointed nail make small dents (2 in. apart) in each piece to mark the places where the holes are to be punched. Punch 5⁄16 in. holes in each piece. If you do this carefully, the holes in the different pieces will match, and the bolts can be pushed or screwed into these. When screwing in the bolt magnets turn them by their heads; do not pinch the coils, as this loosens the wire.
If you have a good punch, it is better to make the yoke as in [App. 27], instead of using separate pieces of tin.
96. Yoke. Fig. 45 and 46. Cut a strip of tin 6 in. long by 3¼ in. wide. Bend one end of it so that it will lap over ¾ in. (Fig. 46); hammer it down gently, then bend this over and over until the whole tin is used. The final result will be a flat roll, 3¼ by about 1 in. This should be hammered flat.
| Fig. 45. | Fig. 46. |
If you have the tools it is easy to drill two 5⁄16 holes in this strip. They should be 2 in. apart; that is, 2 in. from the center of one to that of the other. Start the holes with a center punch.
97. If you have no way of drilling the holes, they must be punched. (See [App. 27].) This will make the strip bulge out on the underside around the holes. This bur, or most of it, should be filed off. (See [App. 79] for method of filing thin pieces of metal.) The resulting yoke may be held firmly to the magnets by the use of 2 extra nuts, as in Fig. 67. Remember that the magnets must be held firmly in the yoke.