Page:Popular Science Monthly Volume 89.djvu/157

 Popular Science Monihli/

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��How to Make an Electric Shaving-Mug

THE general use of electricity in the home has opened up a new fiolcl in the way of cooking and heating utensils. Such appliances are usually sui)i)]ic(i by electrical houses, but many of the uten- sils may be easily and neatly constructed at home. One of these is the electric shaving-mug. A mug or cup, capable of standing heat, is the first thing required. An aluminum cup of standard shape and design, which may be pur- chased in any town, will do perfectly well.

These cups are spun from a flat sheet, and ha\e no seams to open or leak. It is also necessary that no holes be drilled in the mug, since it will be utterly impossible to make such holes watertight again. The heating element must be fastened to the mug with a clamp. This clamp will also allow the heating-coil to be removed for repairs, and makes it easily accessible at all times. The bottom of such a mug commonly has a flange, which makes a recessed part, and in this the heating- element is placed. The legs of the mug are to be made of sheet brass, as shown in Fig. I, one of the three having a hole near the center for an insulating button (Fig. 2), of "transite" or some other material to hold the supply cord in place. The clamp, for holding the heating-coil, is shown in Fig. 3. This clamp has a screw in the center to tighten it in place.

The heating-coil or element is depicted in Fig. 4, which is a coil of flat "ni- chrome" wire, or ribbon, as it is called, 12 ft. long, 1/16 in. wide, and 3 1 000 in. thick. This is equal, in cross-section, to a No. 26 gage wire. To wind this coil, procure a block of wood, Jg-'i. thick, about 4 ins. sq., with a J j-in. hole in the center for an axis or pivot. Clamp a 3^-in. rod in a vise so that the block can be rotated around it. Begin- ning at the center, fasten one end of the nichrome ribbon to the block, lea\'ing about 2 ins. surplus to make a connection. Then proceed to wind the ribbon in a spiral coil, .separating each turn from the preceding one by a strand of asbestos cord.

A small section of this coil, as it would appear higiily magnified, is depicted in

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�� ���Details of the shaving-cup and construction of the heating-coil

Fig. 5, where /I, or the lightly shaded part, represents the asbestos insulation, and B, or the black lines, the ribbon. This asbestos insulates each turn of the coil from the next nearest, and the electrical current must travel entirely through the resistant element, instead of jumping from one turn directly to another, which would be the case, if insulation were not used. The coil must be very closely wound, in order to get it into the very limited space in the bottom of the mug.

Before taking the coil from the block, rub into its surface a little asbestos retort cement, or a cement composed of a mixture of silicate of soda and silica, or glass sand. This mixture, when dry, will tend to hold the coil together, and the current may be passed through the coil, to test it, as well as to bake it in its coiled shape. The support for the coil is a disk made from a piece of 5/'i6-in. asbestos, wood or transite. Cut it to fit into the recessed part in the bottom of the mug. Then with a chisel, remove enough material from the top of this disk to form a depression, 1/16

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