Now have a blacksmith make two [U] pieces of soft iron for the field and armature cores, as shown in Fig. 41. These are of quarter-inch iron one inch and a half in width. They are one inch and three-quarters across and the same in length. One of them should have a half-inch hole bored in the end (at the middle), and above and below it smaller holes for round-headed screws to pass through. By means of these screws the [U] is held to the wooden back. The other [U] is to have a three-eighth-inch hole bored in it so that it will fit on the armature shaft. Wind the [U] irons with six layers of No. 20 cotton-insulated wire, having first covered the bare iron with several wraps of paper. Use thick shellac freely after each layer is on, so that the turns of wire will be well insulated and bound to each other. Follow the wiring diagram shown in Fig. 40 when winding these cores, and when the field is ready, make it fast to the back with three-quarter-inch round-headed brass screws.
Directly in the middle of the hole through the field iron bore a quarter-inch hole for the armature shaft to pass through; then make an [L] piece, of brass, two inches high, three-quarters of an inch wide, and with the foot an inch long, as shown at Fig. 42. Two holes are made in the foot through which screws will pass into the base, and near the top a quarter-inch hole is to be bored, the centre of which is to line with that through the back, at the middle of the field core. The shaft is made from steel three-eighths of an inch in diameter and six inches and a half long. One inch from one end the shaft should be turned down to a quarter of an inch in diameter, and one inch and a quarter from the other end it must be reduced to a similar size. The short end mounts in the back and the long one receives the pulley, after the latter passes through the [L] bearing. A piece of three-eighth-inch brass tubing an inch long is slipped over the shaft two inches from the pulley end and secured with a flush set-screw. This tubing is then threaded and provided with two nuts, one at either end, so that when the armature [U] is slipped on the collar the nuts can be tightened and made to hold the magnet securely on the shaft. This shaft is clearly shown in the sectional drawings Fig. 43.