142 



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 tlie 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 disconnected as the fool is withdrawn.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 



