From hard-wood half an inch thick cut a base-piece six inches and a half long by three inches and a half wide. Arrange this base on cross-strips three-quarters of an inch wide and half an inch thick, making the union with glue and screws driven up from the underside. To one end of this base attach an upright or back two inches and three-quarters high, and allow the lower edge to extend down to the bottom of the cross-strip, as shown at the left of [Fig. 39]. Make this fast to the end of the base and side of the cross-strip with glue and screws; then give the wood a coat of stain and shellac to properly finish it.
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].
At the left side the shaft (S) passes into the wood back through the quarter-inch hole. At the outside a brass plate with a quarter-inch hole is screwed fast and acts as a bearing. The shaft does not touch the field-magnet (F M), because the hole is large enough for the quarter-inch shaft to clear it. A fibre washer (F W) is placed on the shaft before it is slipped through the back. This prevents the shaft from playing too much, and deadens any sound of “jumping” while rotating.
At the middle the shaft (S) passes through the brass collar on which the threads are cut. A M represents the armature magnet, and W W the washers and nuts employed to bind it in place. At the right, S again represents the shaft, B the bearing, C the commutator hub, and P the pulley, while R is the small block under the hub to which the brushes and binding-posts are attached.
From the descriptions already given of dynamos, and with these figure drawings as a guide, it should be an easy matter to assemble this motor.
The ends of the field and armature magnets should be separated an eighth of an inch. The hub for the commutators is three-quarters of an inch long and three-quarters of an inch in diameter. The commutators are made as described for the uni-direction current machine, care being taken to keep the holding screws from touching the shaft. A three-quarter-inch cube of wood is mounted on the base, under the commutator hub, and to this the brushes and binding-posts are made fast, as shown in [Fig. 39]. Unless the armature happens to be in a certain position this motor is not self-starting, but a twist on the pulley, as the current is turned on, will give it the necessary start. Its speed will then depend on the amount of current forced through the coils.
Another Simple Motor
Another type of motor is shown in [Fig. 44], where one field-winding magnetizes both the core and the lugs. The frame of this motor is made up of two plates of soft iron a quarter of an inch thick, six inches long, and two inches and a half wide. Each plate is bent at one end so as to form a foot three-quarters of an inch long, and a half-inch hole is drilled one inch and a quarter up from the bottom, at the middle of each plate. Through this hole pass the machine-screws which hold the iron core in place between the side-plates. The core is made of three-quarter-inch round iron two inches and three-quarters long, and drilled and threaded at each end to receive the binding machine-screws.
Two lugs are cut from iron, and hollowed at one side so that an armature two inches in diameter will rotate within them when made fast to the side-plates. The lugs are two inches and a half long, an inch wide, and two inches and a half high.