Page:Popular Science Monthly Volume 90.djvu/652

 636

��Popular Science Monthly

��power or more. The pattern for the cast- ing should be about 7)^ in. in diameter by ]/s ^^' thick and have an inside diam- eter of 4 in.

The casting should be faced off in a large chuck as shown at A, B and C, Fig. I, and have two circles marked on it of 4% in. and 6-in. diameter. If the constructor has not a large chuck the

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Dimensions of the hub for the rotor which may be made of brass or machine steel

casting may be turned up by screwing it to a flat piece of wood. To do this one must drill about four holes in the casting, countersinking them 1/16 in. below the surface near the outer edges, and fastening to the wooden plate with wood screws.

After the casting has been turned to size it should be removed from the lathe and distances stepped off around the 6 in. circle according to the number of lugs desired. The plate or casting should then be drilled so that lugs }4 in. wide in circumference are formed as shown at D. When only a few lugs are required for the gap, as when used on a high speed motor, it may be necessary to drill several holes together as at E. There should also be six holes drilled with a No. 28-in. drill at points equi- distant on the 4^-in. circle. These are to be tapped out for an 8-32 thread. When this is done the casting should be cut with a hacksaw through the re- mainder of the 6-in. circle, thus giving the rotor shape roughly. It will be found that if before drilling with the i-in. drill a small drill about 1/16 in. in diameter is run through, the i-in. drill will not slip out of place.

For highest radiation it will be found that some frequency between 300 and 800 works best, although the higher

��notes are more easily read through static.

There should be two pieces made of each part shown in Fig. 2 and (except for the handles C) they should be made of copper. Brass will do, however, except for the sparking surface B. The part A is made of }4-in. round rod about 2^ in. long threaded on one end for about ^ in. with a 14-20 die and having a shoulder about 3/16 in. in diameter and }4: in. long on the other end. The parts shown at B are the electrode tips which are made of copper 3>^ by ^ by ^ in. drilled 9/32 in. deep on the side with a 3/16-in. drill. These last pieces may be soldered on the pieces A or may be driven on and secured with a small brass pin. The handles shown at C are about 2 in. long and may be made of black fiber, or wood painted black. Small switch handles, such as are used on 30 amp. iio-volt switches, may be used. The handles should have a 7 732 -in. hole drilled in them i in. deep.

The parts shown at D are made from }4 by i3^-in. copper, 2}^ in. long drilled as shown, two holes with a No. 10 drill about ^ in. from the edges and a ^-in. hole in the center to fit parts shown at G. These pieces are made of ^-in. round rod and are drilled through with a /^-in. drill. There is a No. 21 drill hole for a 10-32 set screw at the larger end. These pieces should be

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��A hardwood block of oak or maple is turned to the dimensions for the frame

soldered into the center of the parts D. Instead of the pieces shown at K, 10-24 hex nuts may be used of a large size so as to look well with the thumb nuts shown at L.

In Fig. 3, A-B IS the hub for the rotor, which may be made of brass or machine steel, i^ in. in diameter. The

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