Page:Popular Science Monthly Volume 89.djvu/961

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�Q Amateur ■ Electrician

��-ksA Wii-eless Operator

��Making an Electrically Heated

Soldering Iron

AN electric soldering iron is not a

x\. tool for the inexperienced person

to build; however, with extreme care and

the proper materials, a very good tool can

���The necessary parts for the construction of an electrically heated soldering iron

be made. An improperly designed and constructed electric soldering iron may often result in fireworks of a dangerous variety. The home-made kind will be somewhat cheaper than one of a similar size and like heating element and just as good results can be had from its use.

The handle is turned in a lathe from maple stock to the dimensions given in the diagram. A hole is bored axially through the handle and a 6-in. length of ^-in. gas-pipe forced into it. Two feet of asbestos-covered copper wire should be led through the pipe and han- dle and to an attachment plug. The other terminals of the wire are attached to the resistance winding. The winding, whose resistance causes the copper head to be heated, consists of i8 ft. of No. 30 nichrome wire, which is wound in six layers on the copper spool. Each layer should be well insulated with leaf mica, and the outer la\er well covered. A protective copper tube is pressed over

��the winding, covering it completely. The dimensions of this tube and of the copper are given in the drawing. Care should be taken that the wire does not come in contact at any place with the metal parts. Without a rheostat the iron will consume about 100 watts.

��An Electric Burglar Alarm Attached to a Door-Lock

A BURGLAR alarm which is oper- ated when a door is opened can be constructed by screwing a spring A in the back wall of the mortise of the door jamb, bending it so that it makes a contact with the lock-bolt, as indicated in the sketch. The spring forms one contact and the iron covering the door, the other. The two contacts thus formed are connected to bell magnets B through a closed circuit battery. The other connections are shown in the diagram.

When the door is locked the bell C will not ring; but when the bolt is

���DOOR CLOSED CIRCUIT B4TTERV

��B/^TTERY

��Spring contact in a door-lock for sounding a burglar alarm when the door is opened

disengaged from the spring the circuit is broken, allowing the armature of the bell magnets to spring back, closing the circuit. — Charles W. Christman.

��947

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