Page:Popular Science Monthly Volume 89.djvu/156

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��Popular Science Monthly

��'Solenoid

���A treadle is used for operating the rheostat of this electrical hammer

A Model Electrical Hammer

AN electrical hammer is simple and practical in construction and, if built to a fair size, may be utilized in doing small and light riveting work, such as jewelers and model makers encounter. A solenoid or suction-type electromagnet forms the basis of the apparatus. The magnet may be about 3 ins. in length, with end disks about 1 3^ ins. in diameter, and a brass or fiber tube of yi-in. inside diameter running through its center.

If a metal tube is used, it should lie properly insulated by several layers of paper. The coil is formed of No. i6 enameled or cotton-covered wire, wound in even layers and filling the bobbin. The two leads are put into the circuit as shown, with the foot-operated controller or rheostat.

A rheostat is fastened at a convenient level; and a string is attached to a small hook on the end of the rheostat handle and connected with a hinged pedal. A stiff brass spring is stretclied between the handle and a point on the rheostat board so that the current is immediately disconnected as the fool is withdrawn.

��A small anvil-iron is attached at the bottom of the point where the iron hammer or plunger drops down. On the lower point, the switch or rheostat breaks the solenoid circuit, allowing the hammer to drop heavily on the anvil or object to be riveted. On the top point the coil receives its greatest power from a battery of from 4 to 6 dry cells, which eventually sucks back or withdraws the plunger into the hollow tube in the solenoid magnet. If the foot is lifted up and down, or the handle of the rheostat operated by hand, the hammer will move up and down forcefully.

Compact Condensers

WHEN mica is used to separate the plates of condensers, the capacity is nearly seven times as great as though the dielectric were simply air. For a given thickness, the voltage may be made about three times that which glass will withstand. Mica is light in weight also, and because of these three features it is being used more and more in radio transmitters.

How to Make an Attachment-Plug

TO make an attachment-plug of an old fuse-plug, first make a hole in the center of the mica cover, so that a socket- bushing will screw in tightly. Take the cover ofT by prying around the edge of the brass ring. Seal the socket- bushing on the inside by heating and shaping it like the outside, then bring the lamp end through the bushing, solder the wires to the cap and screw- contacts, put the cover on, press back the rim in place, and you have an attach- ment plug. — H. L. Baer.

���Insert a socket-bushing in a fuse-plug to form an attachment-plug

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