This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The electric heater described in this article is very simple to construct, its operation exceedingly satisfactory, and the necessary material easily procured at a small cost at most electrical-supply stores. The few tools needed are usually found about every home, and the heater may be constructed by any ingenious person.
Procure 6 porcelain tubes, 20 in. long and approximately 13/16 in. in diameter. On each of these tubes wind 25 ft. of bare No. 26 gauge "Climax" resistance wire. The various turns should be uniformly distributed along the tubes and not allowed to come into contact with each other, which can be prevented by placing a thin, narrow coat of plaster of Paris along the side of each of the tubes immediately after the winding has been put on. Several inches of free wire should be allowed at each end, for making connections, and the first and last turns on each tube should be securely fastened to the tube by several turns of binding wire. It would be best not to extend the winding nearer the ends of the tubes than 3/4 in. Cut from some heavy tin, or other thin sheet metal, two disks, 6 in. in diameter, and punch six 5/16-in. holes in each of the disks at equal distances and within 3/4 in. of the outer edge. Punch two 1/8-in. holes in one of these disks, to be used in mounting a porcelain socket, and also one 1/2-in. hole through which the wires may be led to the socket, as shown in Fig. 1. In the other disk punch four 1/8-in. holes, for mounting two porcelain single-pole snap switches, and two 1/2-in. holes, for leading the wires through to the switches, as shown in Fig. 2.
Cut off six lengths of 5/16-in. iron rod, 22 in. long, and thread both ends of each piece for a length of 1 1/4 in. Fasten the porcelain tubes between the metal disks, by placing one of the rods through each of the tubes and allowing the ends to extend through the 5/16-in. holes in the outer edge of the disks. A nut should be placed on each end of all the rods and drawn up so that the length of rod protruding at each end is the same. Obtain two single-pole snap switches and a porcelain socket, and mount them on the ends by means of some small stove bolts.
The windings on the porcelain tubes should be connected as follows: Let the windings be designated by the letters A, B, C, D, E,and F, and their position be that indicated in Figs. 1 and 2. The primes indicate the ends of the windings at the socket end, and the letters without the primes indicate the ends of the windings at the switch end of the heater. The ends A and D should be connected directly together. The ends B and C to the clips of the right-band snap switch, and E and F, to the clips of the left-hand snap switch. The ends F', A', and B' should be connected to one terminal of the socket, and C, D', and E' to the other terminal of the socket. Electrical connection is made to the winding by means of a plug and piece of lamp cord. It is obvious that the windings A and D will be connected as soon as the plug is screwed into the socket, if the circuit is closed at all other points, and the windings B and C, and E and F are controlled by the right and left-hand snap switches, respectively. Make sure all the connections are properly insulated, and that there is little chance of a short circuit occurring.
Ill: Fig. 1 Fig. 2 Detail of the Two Ends on the Heater Giving Dimensions and the Location of Parts
After the socket and snap switches have been connected to the windings, two more thin disks, the same diameter as the first, may be fitted over the ends and held in place by two units on the end of each rod, a nut being placed on each side of the disks. A better way of mounting these disks would be by small machine screws that enter threaded holes in the ends of the rods. These last disks are not absolutely necessary, but they will add some to the appearance o f the completed heater. Four small ears, about % in. square, should be cut on the outer edge of the outside or inside disks and bent over at right angles to the main portion, to be used in mounting the outside case of the heater.
Cut from a sheet of 1/8-in. asbestos a piece just long enough to fit between the inside disks and wide enough to cover the three lower windings C, D, and E. The object of this piece of asbestos is to protect the surface upon which the heater will stand from excessive heat, since it is to rest in a horizontal position.
Obtain a piece of perforated, thin sheet metal, 191/2 in. wide and long enough to reach from one outside disk to the other. Bend this into a cylinder and fasten it to the lugs on the disks by means of small screws or bolts.
The legs may be made of %-in. strap iron, % in. wide, bent into the form shown in Fig. 3. These pieces may be attached to the perforated cylinder, before it is mounted on the heater proper, by means of several small bolts. The piece of asbestos should be wired to the cylinder after the heater is all assembled, so that it will always remain in the lower part of the cylinder and serve the purpose for which it is intended.
The heater, as described above, is constructed for a 110-volt circuit, which is the voltage commonly used in electric lighting. The total consumption of the heater will be approximately 600 watts, each part consuming about 1/3 of the total, or 200 watts. If it is desired to wind the heater for a 220-volt circuit, 25 ft. of No. 29 gauge "Climax" resistance wire should be used on each tube.