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 



l-iCi.3 



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 



FI6.4 



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 



