Core.—The dimensions and method of assembling the core laminations are indicated by Fig. 44. Long strips are cut from soft Russian or Swedish stovepipe iron. The strips, which are 1 3/4 inches wide are then cut up into short lengths, one half of which are 7 3/4 inches long and the other half 4 3/4 inches. Enough are cut to form two piles of each size 1 3/4 inches high when compressed. The completed core will then form a hollow rectangle 9 1/2 x 6 1/2 x 1 3/4 inches.
Fig. 44. Assembly and Dimensions of Core.
The strips must be dipped in some good insulating varnish such as P. & B. compound and thoroughly dried before they are assembled. Both "legs" (the longest sides) are laid on a table with the alternate ends overlapping as shown by A and B in Fig. 44. After the short pieces C and D have been slipped between the overlapping ends the whole core is squared up. The strips D are then carefully removed and one end of the core thus left open until all the windings are in place. Three or four layers of well varnished linen cloth are wound tightly over the "legs" preparatory to winding on the primary.
Primary.—Four fiber heads, H, 4 3/4 inches square, 1/2 inch thick and having a square hole 1 7/8 x 1 7/8 inches cut in the center are required. One of the fiber heads is placed on each end of the assembled "leg" as shown in Fig. 48.
Fig. 45. Fiber Head and Separator.
The primary winding is wound in six layers, 4 1/2 inches long, three layers on each "leg." About three pounds of No. 16 B. S. gauge double cotton covered magnet wire are required for the winding. The terminals of the two halves of the primary are led through the fiber heads at the same end of the transformer. The windings are not to be carried close up to the fiber heads but begin and end about 1/4 inch from them, so that the remaining space may be filled by winding in a strip of micanite cloth 1/4 inch wide. The primary and secondary windings are separated by a strip of micanite cloth 5 inches wide, wound over both of the primary windings close up to the heads until a layer 1/2 inch thick is formed.
Secondary.—The form on which the secondary sections are wound is illustrated in Fig. 46. All the parts are cut out of wood except the shaft and are made of the dimensions indicated. If the center of the form is slightly tapered it will greatly facilitate the removal of the completed sections. Sixteen sections are required. When removed from the winder they will be in the form of hollow squares 4 1/2 x 4 1/2 x 7/16 inches.
