[Illustration: FIG. 135.—The Assembled Field ready for Winding.]
The armature is one and three-sixteenths inches in diameter. The hole in the field frame which accommodates the armature is one inch and one-quarter in diameter so that there is a space in between for the armature to revolve in.
The hole through the center for the shaft should be of such diameter that the laminations will force very tightly on a shaft one-eighth of an inch in diameter. The laminations should be very carefully flattened and then forced over the steel shaft which is two and one-eighth inches long. Clean up all the rough edges with a file and smooth the outside so that it will revolve properly in the field without scraping.
[Illustration: FIG. 136.—Details of the Armature Lamination.]
[Illustration: FIG. 137.—The Armature assembled on the Shaft ready to
Wind.]
Figure 137 illustrates the armature assembled on the shaft and ready to be wound.
*The Armature Windings* consist of four layers of No. 22 B. & S. Gauge double cotton covered magnet wire wound around each leg. The iron should be very carefully insulated with shellaced paper before the wire is put in position so that there will not be any danger of short circuit due to the sharp edges of the metal cutting through the insulation. Each leg should contain the same number of turns of wire and all should be wound in the same direction.
The Commutator is illustrated in Figure 138. It consists of a piece of brass tubing seven-sixteenths of an inch long, five-sixteenths inside and three-eighths of an inch outside. It should be forced onto a piece of fibre five-sixteenths of an inch in diameter and seven-sixteenths of an inch long. Split the tube into three equal parts by dividing it longitudinally with a hack-saw. Make a fibre ring which will force onto the tube very tightly when it is in position on the fibre core and so hold the three commutator sections firmly in position. The sections should be so arranged that there is a small space between each two and they are perfectly insulated from each other. The fibre core should have a one-eighth inch hole through the centre so that it may be forced tightly onto the shaft and up against the armature after the windings are in position. The commutator should be in such a position that the split between each two sections come directly opposite the centre of each winding. Suppose that the windings are lettered A, B, and C, the commutator section between A and B is numbered 1, that between A and C is No. 2, and the one between C and B is No. 3. Then the inside terminal of B is connected to the outside terminal of A and soldered to the end of commutator section No. 1 close to the winding. The inside end of B is connected to the outside terminal of C and to commutator section No. 2. The inside end of winding C is connected to the outside of B and to commutator section No. 3. The connection of the armature windings to the commutator are represented by the diagram in Figure 139.
[Illustration: FIG. 138.—The Commutator.]
[Illustration: FIG. 139.—Diagram showing how the Armature Coils are connected to the Commutator Sections.]