Popular Science Monthly 



^11 



brass rod with 6 hexagon brass nuts to fit, 

 a number of perfectly flat brass or copper 

 washers of about ^ in. outside diameter, 

 which will slip over the 5/32-in. bolt, a 

 little soft brass strip, two small screws and 

 a hand wheel. In Fig. 6 is shown how one 

 of the 8-32 bolts is used to support the top 

 of each corner of the group of fixed plates 

 in proper relation to the top of the con- 

 denser itself. As indicated, the completed 

 assembly begins at the top with a hexagon 

 nut and washer, after which comes the 

 5-in. square top plate. This is clamped in 

 place by means of a second washer and nut, 

 after which come separating washers to 

 space the uppermost fixed plate the proper 

 distance from the lower side of the insulat- 

 ing top, and then that plate itself. After 

 the first plate, enough washers to make a 

 space of 3-^ in. are put on the threaded rod, 

 and then the next plate. Thus the thirteen 

 fixed plates are placed on and clamped by 

 the nuts of four of the threaded rods. At 

 the bottom, as shown in Fig. 7, the third 

 nut is screwed upward to hold the plates 

 firmly, and a fourth nut turned on to the 

 point which will hold the lowest fixed plate 

 the correct distance from the upper side 

 of the insulating base. After adding a 

 washer, the base itself is placed on, and 

 then a threaded rubber, wood or fiber foot 

 is screwed on to clamp it all in place. Of 

 course, only the corner posts of the base 

 itself take these feet; the two rods at the 

 inner edges of the fixed plates are fastened 

 by screws and washers on the lower side 

 of the base. 



The two corners of the base, shown at 

 the lower part of Fig. 5, where no fixed 

 plates reach, are supported by the fifth and 

 sixth threaded 8-32-rods in the manner 

 shown in Fig. 6 and 7, with the obvious 

 exception that the plates themselves and 

 their separating washers are omitted. 



The Rotary Part 



The moving plates are assembled upon 

 the 5/32-in. threaded rod, clamped by the 

 hexagon nuts and separated by the larger 

 washers, as shown in Fig. 8 and 9. Begin- 

 ning at the top of Fig. 8, it is seen that the 

 hand-wheel, which may be a knurled disk 

 of J<^-in. hard rubber 2 in. in diameter, is 

 clamped at the top of the 5/32-in. rod or 

 shaft between two washers and nuts. Be- 

 tween the lower nut and washer there is 

 gripped the end of a bent metal indicator- 

 hand which points to a degree scale (a 

 cheap protractor makes a good one) 



mounted on the upper side of the insulating 

 top. Just below this lower nut is a little 

 brass bushing or tube, forced into the in- 

 sulating top and having the right inside 

 diameter to act as a bearing for the shaft. 

 Below this come separating washers— one 

 or more — and then two nuts which lock each 

 other and hold the moving plates in place. 

 The uppermost moving or semi-circular 

 plate comes next; immediately below it, 

 and separating it from the next plate, are 

 enough of the larger washers to space the 

 plates just 14: i"- apart. 



As shown in Fig. 9, the moving section is 

 built downward, and the lowest plate is 

 clamped in place by two more nuts. The 

 shaft itself continues for about yi in. farther, 

 and is tapered off to a blunt point so as tc 

 reduce friction. 



The Lower Bearing 



In Pig. 9 is also shown how two pieces 

 of I 'i6-in. soft brass strip are bent and 



The machine screw fastening at the upper 

 and lower corners and the main shaft bearings 



drilled to form a thrust bearing for the 

 lower end of the shaft. They are secured 

 to the base or lower 5-in. square insulating 

 plate by the two machine screws. Elec- 

 trical connection is made to the moving 

 plates by soldering a wire to one of these 

 screws, running it out to one of the corner 

 screws which is not associated with the 

 fixed plates, and once more soldering it 

 there. A binding post takes the place of 

 the top nut of Fig. 6 on this outside screw. 

 Similarly, a second binding post substi- 

 tuted for the uppermost nut on one of the 

 screws supporting the fixed plates provides 

 a convenient means of connection with the 

 fixed plates. 



For continued service it will not do to 



