Popular Science Monthly 



637 



four small holes should be drilled with a 

 No. 21 drill and threaded 10/32 and the 

 center hole should be the size of the 

 motor shaft. The insulating bushing 

 between the hub and the rotor casting is 



II 



U 



The cover for the casing is of black sheet 

 fiber and is screwed on like a cylinder head 



made of black fiber 5^ in. in diameter 

 and turned as shown. It will be found 

 worth while to corrugate the sides with 

 a round nose tool as shown at D, as 

 this reduces surface leakage and im- 

 proves the appearance of the rotor. 

 The fiber piece should have No. 18 drill 

 holes in it to correspond with those on 

 the 4% in. circle of the casting C. 

 There should also be No. 10 drill holes 

 at the center corresponding to those in 

 the hub. The rotor may then be as- 

 sembled with round head screws and 

 balanced. This may be done by putting 

 a small piece of rod the size of the shaft 

 in the hub and fastening it securely with 

 the set screw. It should then be rested 

 on parallel knife edges and drilled out at 

 various points on the back toward the 

 inner edge of the casting until it will rest 

 at any position. The knife edges must 

 be set absolutely level. 



The wooden block shown in Fig. 4 is 

 of quartered oak or maple and is 23^ by 

 8 by 8 in. This block should be planed 

 absolutely square. If it is turned off 

 center as shown, the casing will be more 

 accurate than if the block were turned 

 and then the three sides cut off. The 

 block should be hollowed out 63^ in. in 

 diameter and i^ in. deep and drilled as 

 shown in the illustrations. 



The holes in the bottom of the block 

 are for mounting it on the base, Fig. 5. 

 C, and a center hole about 3/16 in. in 

 diameter should be drilled for a 3/'i6-in. 

 flat head bolt, and 1/ 16 in. on each side of 

 it to receive a wood screw from the base. 

 The three holes in each side should 

 correspond to those in electrode plates. 

 (Fig. 2, D. E.) 



The fiber cover for the casing is 

 shown at A-B, Fig. 5 and is made from 

 5/16-in. black fiber sheet. The small hole 

 around the periphery should be 5/16 in. 

 in from the edge and drilled with a No. 18 

 drill to allow the use of about ^^-in. 

 round head brass wood screws to fasten 

 cover to wooden casing. The large 

 holes shown are for small circular 

 windows to observe the spark and for 

 adjustments. 



For glasses, the lenses of the cheap 

 grade of automobile goggles ma\- be 

 used by cutting all the metal away 

 except a small rim around the glass. If 

 you have not a drill of the proper size 

 one can be improvised, as shown at Z>, by 

 taking a piece of ^^-in. machine steel 

 with a rectangular hole cut through it 

 and a piece of hardened tool steel about 

 /€ by /^ in. driven in and ground to a 

 cutting edge. When using a drill of 

 this sort, a hole the size of the machine 

 steel — ;^ in. — will have to be drilled 

 through the cover. Drill about 1/16 in. 



fiG.C> 



Three views of the gap, as it is attached 

 to the motor and the front and back sides 



deep on each side of each hole the exact 

 size of the glasses and then grind off the 

 drill about i/i6in. on the radius and con- 

 tinue the hole through. The glasses 



