A VERTICAL POWER MOTOR
The Field Frame is shown in detail in Figure 60. The exact shape and dimensions are best understood by a careful examination of the drawing.
The pattern for the field may be made of the same shape and practically the same size as indicated for the finished casting because the "rapping" or jarring which the pattern will receive in the foundry in order to free it from the sand mould will enlarge the mould sufficiently in a casting of small size to make up for any shrinkage which takes place upon the cooling of the iron.
The only exception to this is in the tunnel where the armature rotates. This should measure one and three-quarter inches in diameter when finished and should be slightly smaller in the rough casting so that there is enough material to allow for truing and bringing to equal size.
The Armature may be of two types, three pole or six pole. The three-pole armature is the simpler, but the six-pole type is the smoother running and gives the steadier power. The details and dimensions are shown in Figures 61 and 62. One of the armatures should be selected and a pattern built.
FIG. 61.—Three-pole Armature.
After the patterns are finished they should be given a coat of shellac and carefully rubbed with fine sandpaper so that they are perfectly smooth. Otherwise the sand is liable to stick in moulding and produce an imperfect casting.
Castings may be obtained from any foundry which is equipped to make grey iron castings. They should be as soft as possible. The cost will depend upon the quantity which are ordered. If only one set is required, the charge will probably be based upon the time required for making the moulds but if several sets are ordered the price may be based upon the weight.
After the castings have been received from the foundry, the first operation is to carefully remove all rough spots and burrs with a file.
Those who have a lathe or large drill press can easily finish the tunnel by turning or reaming. In the absence of these facilities, hand filing can be made to suffice, if carefully done.
The holes marked "BBBB" should be drilled with a No. 29 drill and tapped 8-32. These holes must be very carefully located because they serve to fasten the bearings. Each hole should be exactly opposite the other, two and five-sixteenth inches apart and on a line passing exactly through the centre of the tunnel.
The holes, "PP" and "SS", are three-sixteenths of an inch in diameter. The former support the Binding Posts and the latter pass the screws which fasten the motor to the wooden base.
FIG. 62.—Six-pole Armature.
The armature, in the case of either the six or three pole type, has a three-sixteenth inch hole drilled along the axis to accommodate a steel shaft of the same diameter.
The armature casting should be accurately turned to a diameter of one and twenty-three thirty-seconds of an inch so that it will revolve in the tunnel without touching the field but still be very close to it.
Two holes bored through one of the pole pieces at right angles to the shaft with a No. 37 drill and threaded with a 6-32 tap will allow the armature to be clamped tightly to the shaft with two headless set screws.
The Field Winding consists of No. 16 double cotton insulated wire. Before the winding is put on, the core should be insulated with one or two layers of shellaced paper. Two circular pieces of shellaced paper should be placed against the flanges at the end of the core, so that the winding space is thoroughly insulated and there is no liability of the wire touching the iron at any point. The wire should be wound in smooth even layers. The winding space is completely filled. The outside layer may be finished by a coat of shellac.
The three-pole armature is much easier to wind than the six pole type. The wire used should be No. 24 B. & S. Gauge, double cotton covered. Before the wire is wound on, cover the winding space with shellaced paper so that the wire will not touch the iron at any point. Each coil should be wound in the same direction as the others starting at the same end and as close as possible to the inside.
FIG. 63.—Showing how the Coils on a Three-pole Armature are connected to the Commutator.
The outside end of each coil should be connected to the inside of the next coil as shown in Figure 63. The diagram indicates only one layer of wire in each coil for the sake of clearness.
The winding upon the armature shown in Figure 64 is divided into six coils. Each coil consists of as many turns as possible of No. 24 B. & S. Gauge, cotton covered wire to fill the space completely and all coils are wound in the same direction. The illustrations show the various stages of the bindings with the two, four and six coils in place. The winding spaces on the armature should be carefully insulated with shellaced paper before the coils are placed in position.
After the winding has been finished the next step is to make the shaft and commutator. The shaft is a piece of three-sixteenths steel, three and one-quarter inches long. The shaft passes through the centre of the armature and is locked-in position by the two set screws.
The Commutator is probably one of the most difficult parts of the motor to make. It consists of three circular brass sections insulated from one another on a fibre bushing.
The fibre bushing is a hollow cylinder, five-sixteenths of an inch in diameter and seventeen thirty-seconds of an inch long. The bushing should force tightly on the shaft. The segments are make by turning a piece of three-quarter inch brass rod in a lathe until it is one-half an inch in diameter for a distance of about seven-sixteenths of an inch. A five-sixteenths inch hole should be bored through the center so that it will fit tightly upon the fibre bushing.
FIG. 64.—Showing how the Coils on a Six-pole Armature are arranged and connected.
Then cut the brass off one-half inch from the end so that it leaves a flange at one end, three-quarters of an inch in diameter. Saw it lengthwise into three equal parts and mount it upon the fibre bushing with a small strip of mica between each two sections to fill in the space made by the saw cuts. The sections are held together by a fibre ring, three quarters of an inch in diameter outside and one-half an inch in diameter inside. The ring should fit very tightly over the commutator and be forced down flush against the shoulder. After the ring is in position, file any mica which may project out of the slots down even with the surface of the segments and force the commutator onto the shaft with the shoulder against the armature. The commutator must fit very tightly so that there is not any possibility of moving it after it is in position.
FIG. 65.—Details of the Commutator.
The sections should bear a certain relative position to the armature windings. The diagrams in Figures 63 and 64 show the proper position for the three and six pole armature respectively.
The coils are connected to the commutator by soldering the terminals to the shoulder on each segment. This work should be very carefully done so as to insure a neat job and connection of the proper terminal to the proper section.
FIG. 66.—Details of the Bearings, Shaft, and Pulley.