A New Rotary Variable Condenser 



A simplified method of construction 

 within the scope of the amateur 



By R. U. Clark, 3d 



THE innovation which the author has 

 worked out for building rotary con-' 

 densers, consists in separating the 

 fixed and movable plates the correct dis- 

 tance from each other by means of a simple 

 lead casting for each set. 



The instructions outlined herewith make 

 it a simple matter to construct two excellent 

 rotary condensers, at a small cost and with 

 little labor. The tools and materials 

 required are readily obtainable. 



The dimensions specified are those em- 



MARE 12 CF NO 22 

 ALUMINUM 



MAKE 11 Of tO.26 

 ALUMINUM 



MAKE £4 Of NO +0 

 CARDBOARD 



Dimensions of aluminum, brass and card- 

 board plates for making a rotary condenser 



ployed in making the complete condenser 

 illustrated. Although the fixed plates in 

 this view may appear rather far apart, as a 

 matter of fact they are separated by only 

 5/64 in., and nearly half of the space 

 between them is taken up by the rotary 

 plates; also it should be noted that the 

 greatest diameter of the condenser casting 

 is but 3J<^ in. 



In the completed condenser, the fixed and 

 movable plates are separated only 1/40 in. 

 which makes the instrument very compact. 

 The fixed plates are 3 in. in diameter and 

 1/64 in. thick. The rotary plates are also 

 relatively larger, in prop)ortion to the size of 

 the fixed plates, than is the rule in con- 



densers. The rotary plates are made of 

 thicker material than the stationary ones in 

 order that they may have maximum flat- 

 ness of surface, and also that they may hold 

 their trueness better. This makes it pos- 

 sible to separate the fixed plates a greater 

 distance, which is desirable for many 

 reasons. In case the experimenter should 

 desire to make the clearance of the plates 

 less than specified, thicker rotar>' plates 

 should be used. The space betv\een the 

 fixed ones, however, should not be di- 

 minished. 



The tools required in making the con- 

 densers are as follows: one coping or jig- 

 saw, and one hack-saw; one 17/64-in., one 

 3^-in. and one 3^in drill; a small vise, 2 

 small clamps, a drill stock, and a flat file. 

 These are practically the only tools abso- 

 lutely necessary^; however, certain con- 

 venient accessories will be mentioned from 

 time to time in the course of this article. 



The materials required are as follows: 



Two 3-in. round brass disks, 1/16 in. thick. 



One aluminum sheet about No. 22 gage, 12 by 9 in. 



One aluminum sheet about No. 26 to 28 gage, 

 12 by 9 in. 



Smooth cardboard or bristol board, 1/40 in. 

 thick, and of sufficient area to make thirty 3-in. 

 disks. 



Two pounds of lead. 



Two brass machine screws, round or fillister head, 

 about 2 in. long by J^ in. in diameter, with nuts. 



One piece of fiber 2 by i in., and 3/16 to }4 in- 

 thick. 



Eight flat head brass machine screws about ^i by 

 5<t in. with 16 nuts to fit. 



Two hard rubber or composition typewriter roller 

 knobs with long metal bushings. 



Four small binding posts fitted with flat headed 

 brass bolts. 



Two old disk records, or ten-cent phonograph 

 records. 



One round pasteboard box about 3H >"• in 

 diameter by about i H »n. deep. 



The first step is to cut the sheet alumi- 

 num into 3-in. squares. This can best be 

 done on a tinsmith's cutting machine, or 

 with bench shears, as when cut in this 

 manner the thin metal will not be bent, and 

 none will be wasted in clippings. When 

 this has been done the thin sheets should be 

 cut into 3 in. circles, and the thicker pieces 



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