The complete engine is shown in Figure 50. All the various parts have been marked so that you can easily identify them in the other drawings. It is well to study this illustration carefully so that you will understand just how all the parts are arranged.
The Base is illustrated in Figure 51. It is made of a piece of hardwood, seven inches long, three and one-half inches wide, and one-half an inch thick.
The Electromagnets will largely determine the dimensions of the rest of the engine. The magnets shown in Figure 52 are made of three-eighths inch round iron two and one-half inches long, provided with two fibre washers one and one-eighths inches in diameter. On end of each of the steel cores is drilled and tapped to received an 8-32 screw. The experimenter may possibly be able to secure some old magnet cores fitted with fibre heads from an old telephone bell or "ringer" as they are sometimes called. A suitable bolt may be made to serve the purpose by cutting it off to the right dimensions with a hack saw. If a drill and tap are not available for drilling and tapping the end so that the core can be properly mounted in the frame of the engine, it is possible, to use the threaded portion of a bolt to good advantage, by the exercise of a little ingenuity. The hole in the frame should then be made larger so that the end of the bolt will slip through, instead of an 8-32 screw and the core clamped in position by a nut on each side.
The fibre washers are spaced two and one-sixteenth inches apart. The space in between should be wound full of No. 18 B. & S. Gauge cotton covered magnet wire. Before winding in the wire, cover the core with a layer of paper so that the wire does not touch the metal. The ends of the wire should be led out through small holes in the fibre heads.
FIG. 52.—Details showing the size of the Magnet Bobbin.
It is not absolutely necessary to use No. 18 B. &.S. Gauge wire in winding the magnets, but it is the size which will give the best results on the average battery. If you use larger wire, the engine will require more current from the battery. If you use finer wire, a battery of higher voltage will be necessary. The current consumption will, however be less.
The electromagnets are mounted in the frame of the engine by means of two screws passing through the holes E and D. The details of the frame are illustrated in figure 53. It is made of a strip of wrought iron or cold rolled steel, five and five-eighths inches long, an inch and one-eighth wide and one-eighth inch thick.
The material for making this part of the engine and also the bearings can best be obtained at some blacksmith shop or hardware store. Heavy galvanized iron can be used but it is not usually thick enough, and it may be necessary to use two thicknesses. The ends of the strip are rounded and bent at right angles so as to form a U-shaped piece with sides one and three-quarters inches high.
The holes, "D" and "E", should be large enough to pass an 8-32 screw. The holes, "A", "B" and "C" should be about one-eighth of an inch in diameter. They are used to pass the screws which hold the frame of the engine to the wooden base.