Before assembling the frame finally, it is well to put the wood into a moderately hot oven for half an hour and thoroughly bake it. After doing so, while the wood is still hot, coat it all over with white shellac. Let this coat dry thoroughly, and then give it another. This portion of the frame may now be laid aside for the present, and the mounting of the glass plates considered. Procure two large spools, such as patent thread is sold upon, and some cigar-box wood, which should be a little thicker than the glass of the plates. Also get a piece of thin sheet brass, about No. 26 stubbs gauge, 10" x 4", a piece of 1/4" steel rod, smooth and round, 9" long, and 10' of No. 10 brass wire. At a store where they sell iron bedsteads get 9 of the 1/2" and one of 3/4" round brass balls such as are used to ornament the bedsteads. From an electric supply house get two pieces of hard rubber tubing 3/4" outside diameter and 91/2" long.
We will now proceed to mount the glass plates. Take your \" round steel rod, K (Fig. 3), and having clamped it firmly in a vise, cut from your sheet brass two pieces 21/2" long and 7/8" wide, and bend them around the rod K, into two tubes, L, 21/2" long and 1/4" inside diameter. Now seam out the holes in the two spools, M, very slightly until the two tubes can be pushed into them without being squeezed together. From your cigar-box wood cut out with a sharp knife two circular pieces of 3" diameter and two of 3/4". Mark the centers, and bore a 1/4" round hole in the exact center of each. Take one of the spools and nail one of the 3// pieces, N, on one end, so that the hole in N corresponds exactly to that in M. The 3/4" piece, O, is then fastened to the face of N, observing the same precautions to get the hole in O opposite that in N. This is very important, as any eccentricity in O will make the plate turn unevenly. Glue a ring of paper, P, on the face of N, and slipping the glass plate into place so that it rests against N with the circle O projecting through the hole in the glass, take two very small screws, R, and screw them into N through the notches in the plate mentioned earlier. These will prevent the plate from turning.
To test the mounting for accuracy, slip the spool and plate over the rod K, for an axis, and spin the former gently round. It should turn easily, but not be loose enough to rattle, and the glass must revolve smoothly and evenly without wobble or eccentricity. If any such defects appear, the plate should be loosened from the spool and adjusted by shifting until it runs truly. When this position is found and marked, remove the plate, and coat both paper ring and plate with Van Stan's cement, and replace the glass, pressing the cemented surfaces together and putting in the screws again to hold all firm. The use of the paper is to allow the thorough adherence of the glass to the wood, the paper acting as a connecting link between the two. The other plate having been mounted in a similar manner, both should be laid away until the cement sets, which will take a couple of days.
We will now take up the making of the collecting combs and dischargers, shown in Fig. 4, in perspective. Take the hard rubber tubes, S, and fit to them two round plugs, T, 3/4" long and thick enough to fit tightly into the tubes. Through the center of these plugs bore 3/16" holes and drive a 1/4" machine screw 11/4|" long through the holes, so that 1/2" of thread projects from the end of the plugs. Cut from the No. 10 brass wire two pieces of 91/2" long and bend them as shown in U, with a partly closed ring at the center, 1/4" inside diameter, and then out in opposite directions at an angle of 45 degrees for 1", then straight again for 31/4"/. The bends should be made symmetrically, so that the 31/4" arms are parallel and 2" apart. The four ends of these arms are scraped bright with a file, and wet with soldering fluid, and four of the 1/2" brass balls are soldered on the ends by the following method : Heat the ball for a few moments, place in a vise and pour melted solder in the hole until the ball is full. While the solder is liquid, insert the end of one of the arms for \" and hold until the solder sets. Smooth all roughness from the joint with a fine file and emery paper. The combs, V, are made from strips of brass 3 long, 1" wide, with saw teeth 1/4" deep cut in the edges, as shown. The strips are folded lengthwise over the 3/4" arms, so that the teeth of the two sets face each other, and are soldered to the arms.
For the arms, W, two pieces 6" long are cut from the No. 10 wire. One end is bent in a ring 1/4" inside diameter, and the joint of the ring is closed with solder and smoothed. In constructing the machine throughout, care must be taken to avoid sharp edges and corners, to prevent the escape of electricity, excepting of course the teeth of the combs. The other end of the arm, W, is turned up for 1/4" and holds a 1/2" ball, X, soldered to it, as before described. In the top of the ball X a 1/8" hole is drilled, which acts as a socket, in which the rod Y, 9" long, can swing loosely to and fro. One of the rods marked Y is tipped with a 1/2" ball, the other with the 3/4".
We will now make what are called the neutralizing bars. Cut two pieces 24" long from your brass wire, A' (Fig. 5), and bend them into half-circles 10" in diameter. Solder strips of brass, B', 1" long x 1/2" wide across each wire at its center, and drill a small hole at each end of the strips. From your broomstick cut two sections 1/2" long, C, and bore a 3/16" hole through the center of each. The wires A' are now fastened by the strips B' to the end of the wooden blocks C, as shown in Fig. 5.
Our next job is to make 64 sectors of tin foil to be placed on the glass plates. Fig. 6 gives the size and shape sector required. The best way to cut these sectors is to make a die stamp of sheet tin 1" wide nailed to a piece of wood corresponding to the outline of Fig. 6. The ends of the tin should be soldered and the cutting edge filed away until fairly sharp. A block of wood 3" x 4", sawed square across the grain, is used for a cutting board. Buy seven or eight sheets of heavy tin foil (it comes about 6" x 8") and fold it into a package 31/2" long x 11/4" wide, having ten layers of foil in it. Lay this package on top of the cutting block and place the die stamp, sharp edge down, on it, leaving a margin all around. If a flat piece of wood is now laid on top of the stamp and struck gently with a hammer, the stamp will drive through the layers of foil, cutting the ten sectors out neatly. This operation must be repeated seven times, which will give us several extra sectors in case we spoil any. We will now take one of the 15" circular cardboard patterns and, from the original center, draw two circles, one 14" and one 11" in diameter. Divide the outer circle into 32 equal parts, and draw lines from the center of the circle, cutting these divisions. The glass plates should now be laid on the cardboard discs, spool side up, so that the edge of plate and edge of card coincide. The lines on the card will show plainly through the glass and are used as guides for attaching the tin-foil sectors. These are wet on one side with shellac, and attached to the upper side of the glass, upon the space between the 14" and 11" circles, with the center of each sector over one of the 32 radial lines.