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Frictional Plate Electric Machine

By Hans Konwiczka

What parts enter into the construction of the machine and how shall we procure them? The single parts are very few and can be made at home, with the exception of the glass plate.

1. Glass plate with shaft and bearings.
2. Baseboard.
3. Friction cushion.
4. Conductor with the collector.

As regards the procuring of these parts, usually the raw material will be right at hand. The glass plate must be completely free from bubbles and cut to a true circle. The wooden parts are made of dry hard-wood, and to make the amalgam for the cushion some mercury from a broken barometer may be available. A few screws are required, and also a brass wire a foot long, and about one-quarter inch thick, a piece of a clock spring, a large spool, and a glass rod about ten inches long and one-half inch thick. A ball from a child's ten-pin set, from 2 1/2 to 4 inches diameter, may be found among some old discarded toys. If not, one can be purchased and work can be begun.

1. Glass Disc with Shaft and Supports
We must get a plate-glass disc about .2 inch thick of 8 inches in diameter; this must be free of bubbles and its edges must be smoothly rounded. A hole about one-quarter inch in diameter must be drilled through the middle for the shaft. To prepare the shaft for the glass disc, bend the three thirty-second inch brass wire as shown in Fig. 1. This provides the straight shaft part about seven inches long, and the crank or handle. Six inches from the end of the straight part a groove, one twenty-fifth inch deep, is filed, whose object will be seen later. To fasten the glass disc to the shaft cut the spool into two parts (W W), Fig. 2; these turned around end to end are stuck upon the shaft (X), and fit it very tightly.

If the glass disc is clamped between the two parts of the spool (WW) and cemented by means of a solution of shellac in alcohol, it will hold its position very well. The shaft is cemented to the halves of the spool (WW) by the same shellac. Before applying the shellac, these parts are to be warmed, the glass plate with greatest care, so as not to break it.

The shaft rests during its revolutions in the two bearings in Figs. 3 and 4, at the top of the standards (AA); these standards are made of hardwood about three-quarter inch thick. They are 9 inches high and 1 1/2 inch wide. The dovetails (N) are for morticing into the baseboard. The mortices must be notched out to fit the dovetails. The standards are eventually glued to the baseboard, and are also secured by a couple of screws. The shaft can be thrust through the one bearing and is dropped into the other one. Fig. 4 shows how one of the bearings is a notch. The bottom of the open bearing is cut to form a wedge, Fig. 4a, which enters into the groove, made around the shaft, so that the shaft can shift neither to right nor to left.

2. The Baseboard
We now have to make a strong base- board. Like all the other woodwork, this must be made of extremely dry wood, and for it we use a solid board about 16 inches long, 8 inches wide, and 7/8-inch thick, Fig. 5. About 3 1/2 inches from one end we make tile two notches (N, N) for receiving the dovetails of the two standards. These must fit the notches perfectly. The standards are at once to be glued fast and secured with screws.

3. The Cushion
Cut four boards (L) of the form shown in Fig. 6 out of cigar box wood. They are about 3 inches long, 1 7/8 inches wide at the bottom and 1 3/8 inches wide at the top. Two of them are provided with very thin cloth which must project a little on one side. These two boards are fastened to a fork made of highly elastic brass strips or out of a piece of our clock spring (F), Figs. 7 and 8. A piece of the spring about 51/2 inches long is perforated in the middle and at both ends with four holes, Fig. 7. It is bent into a U-shape, Fig. 8, which leaves each prong about 2 1/2 inches long. The boards (L) and (L) are screwed tight to these prongs; two pins are driven through each of these boards so that they project about .1 inch from the same and are used for securing the other equally solid boards, so that these last may be real cushions. They are covered on the inner side with thin, soft felt. This spring is attached to a block of wood (B). Figs. 10 and 11, with screws; this block is one inch high. three- quarters inch wide and thick. It has on the side opposite to tile spring a hole three-quarters inch deep (B) for receiving the glass rod (J), Figs. 10 and 11.

From a glass rod one-half inch thick we cut off a piece 2 1/2 inches long and cement it with one end in the block (B), Figs. 10 and 11 of the rubbers. The other end is cemented in a hole directly under the shaft of the glass plate which lies In the center between tile two uprights; the hole is three-quarters inch deep. A short pin, Fig. 9, which has a head at one end of it, is first driven into the block. This pin and the friction cushion to be amalgamated presently must be connected electrically one to the other by a strip of tin-foil. The frictional cushion is to be spread over with the so-called Kienmayer's amalgam. It consists of two parts of mercury, one part of zinc and one part of tin. Tile amalgam is rubbed on with the finger-tips until a thick gray coating is produced. If the amalgam does not stick well a little lard is added to it. The friction cushions are now so strongly pressed against tile corresponding boards which are attached to the spring, that the pins are forced into the un-coated side of the cushion boards. The cushions by the action of the springs and the outer boards are so firmly pressed against the glass plate that tile amalgamated side rubs strongly against its surface.

4. The Prime Conductor
Consists of a hollow brass ball, 3 to 4 inches in diameter. As we could not easily spin up such a ball, we will make our prime conductor of wood and cover it with tinfoil, as shown in (C), Figs. 10 and 11. The ball is bored completely through, exactly following its diameter in any desired direction. Through this hole we thrust a brass wire (V), Fig. 11, about one-eighth inch thick to which a fork (B) is soldered at one end. The wire is six inches long and the folk made out of the same wire as (V), is three inches long. The space between the prongs of the fork is nearly one half inch. It is provided with teeth as shown in Figs. 12 and 13, made out of thin brass pins and soldered so as to be exactly opposite each other on the two sides. These teeth or points are so long that they do not touch the glass plate which turns between them, Fig. 13 (Z), yet they must be as near as possible thereto. The other end of the straight wire projecting from the prime conductor has a small brass ball (D), Figs. 11, 12 and 13 upon it.

We now have to drill a hole in the prime conductor at right angles to the original one, to receive the glass rod which has to carry the whole affair. The glass rod must be so long that the fork will be supported at the level of the shaft of the disc, Fig. 11. It follows that if we insert it five-eighths of an inch in the prime conductor and the same depth in the baseboard it would have to be seven inches long. We now cement around the wooden balls crosswise two strips of tinfoil a little over one-half inch wide, Fig. 14, and cover the whole surface with aluminum bronze. It will be better to cover the whole surface with tinfoil, but as this is quite difficult the simpler method will generally be pursued. The surface of the ball must be perfectly smooth. Finally, we glue to both the outside boards of the cushion two wings of stiff silk of the form shown in Fig. 11. They are stitched together along the edge; i. e., the glass disc, Fig. 11, turns between these two pieces; these wings must reach from the friction-cushion almost all the way to the points of the conductor. The machine must always be turned in the direction from rubbing friction cushion to the points of the conductor in the direction of the arrow, Fig. 11.

Cracked phonograph plates made of vulcanized rubber or ebonite can be used in- stead of the glass plate. Such plates can sometimes be procured for little or nothing. In this case, instead of the amalgamated felt cushions, cat skin with the hair on must be used.

And finally time baseboard must not stand flat upon the table hut must be provided with four short feet glued to it. All the wood parts are gone over with a good varnish. For exciting the machine there is hung to the ball (C) or (D), Fig. 11, a brass chain such as we find in Swiss clocks, which is connected to a gas or water pipe.

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