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Page:Popular Science Monthly Volume 90.djvu/971

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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-




��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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