We now want a piece of rather stout brass wire bent into the shape shown in Fig. 4. It must be about four inches long, but its length will be determined by the size of the drum and the length of the magnet when it is all put together. At the end of this wire you must have a wooden knob (not brass, which doesn’t produce nearly so much noise). This you will have provided ready for you if you purchase the drum, as they will naturally supply drumsticks with it, and the head of one of these cut off and fastened to the end of the wire, by simply making a hole and sticking it in, will answer the purpose beautifully.
This wire has to be fastened to the soft iron armature, a simple way of doing which is to drill a hole the exact size and insert the end; it can then be soldered in. Or, if you cannot drill a hole, you can simply solder it on. The brass spring has the end bent outwards, as shown in Fig. 4, and is fastened to the soft iron armature by screws, as shown in the figure at S S, or simply soldered on. The point C is the end that is tapered off, and the platinum wire is fixed at that point; the spring should extend about 1¼ inch beyond the armature at the other end. Two holes are drilled in the spring at the points H H, through which screws are passed into the support. This support may be either a piece of iron ½ inch long, ¾ inch broad and ¾ inch thick, or a piece of wood will answer very well, and save drilling holes in the iron. If it is wood it had better be larger, say ¾ inch by ¾ inch by 1¼ inch.
PART IV.
We can now proceed to fasten all the parts together. We must have a piece of hard wood for the base, about 3½ inches by 3 inches and ⅜ inch thick. On this the magnet has to be fastened by its support being screwed firmly down. In front of it the armature has to be fastened at such a height as to be exactly in front of the poles of the magnet. The relative positions of the parts are shown in Fig. 5, so I do not think a detailed account of their exact positions on the base is at all necessary.
There is, however, one piece of the mechanism in the figure to which I have introduced you, this is the contact-screw shown at C. To make this we take a piece of brass about 1½ inch long, ½ inch broad, and rather less than ⅛ inch thick, and bend it at right angles, so that one leg is one inch long and the other ½ inch. Now in the part that is ½ inch have to be drilled three holes to fasten it with nails or screws to the base. The other part, one inch long, will then stand erect, but before fastening it in its place we put it to stand in front of the magnet and mark a point which is exactly on a level with the piece of platinum foil on the spring, when the spring and magnet are fixed in position. A hole has now to be drilled through that point and tapped to admit a brass screw with a milled head, and fix the piece in which the screw works to the front hole, so that the screw will work through it.
Fig. 5.—Interior Mechanism of Drum Complete.
M, Magnet. Y, Yoke of magnet. B, Brass support of magnet. A, Armature of soft iron attached to S, spring fastened to armature by screws at P, and to support by screws at H H. T, Support of spring. D, Head of drumstick. W, Wire supporting head of drumstick. C, Contact screw and support. The wire from one coil is joined to brass spring at H H. The wire X, coming from the other coil, and K, the wire from the contact-breaker, are joined to battery. Positions of screws joining parts together are shown by dotted lines. The side marked Z is placed at the bottom when fixing into the drum.
The point of the screw has now to be cut off and a very small piece of platinum wire fixed at the end. This wire will now come in contact with the platinum foil on the spring, when the brass support is fixed in a certain position on the base, and it is now to be fixed in that position with screws or nails. It should be so fixed that when the screw is turned till it is nearly out of its hole the wire is just out of contact with the platinum foil on the spring. It is now evident that by turning the screw one way you make the spring vibrate more rapidly, and by turning it the other way its efforts are relaxed.
The contact-breaker screw having been fixed in its place, and the support of the spring also fixed as at T in the diagram (Fig. 5)—by screws through the base into the iron, if it is made of iron, or by nails or screws through it into the base if of wood—all the parts are now together, and all that remains to be done is to make the necessary connections. One wire that comes from the magnet is to be joined (soldered, if possible,) to the spring at H in the picture; the other wire is left loose. To the brass support of the contact screw we solder another piece of wire. Now this piece of wire is connected with the zinc of the battery and the other (coming from the coil of the magnet) with the carbon of the battery. What happens?