done by using a round file which will almost fill the slots. The slots should be filed until all the projections are smoothed down even.

The portions of the shaft which are to be overlaid with the wire coils should be covered with either adhesive tape or paper shellacked and wound on.

In no instance should the wire be allowed to come in contact with the metal.

Fig. 44 shows the armature completely assembled and ready for winding.

CHAPTER XI

ARMATURE WINDING

The winding of the armature is an operation requiring some care in order to get the required number of turns of wire in each slot.

There are eight circular slots to be filled and eight coils of wire, each coil consisting of sixteen turns of No. 20 double cotton-covered wire. As the wire has to pass through one slot and return through the slot diametrically opposite it is at once apparent that when the coils are all complete there will be thirty-two wires lying in each slot.

Before the winding is started it will be necessary to clean out carefully all burrs or projections from the slots either with a reamer or a round file.

A piece of hard wood or fiber should be prepared as shown in Fig. 45.

This is to be used to straighten and press down each wire into its respective place as it is laid into the slot.

At the ends of the slot the wire will pull down tight of itself, but along the center of the slot there is a tendency to build up in such a way that the slot would be completely filled at that point before the required number of turns were in place, if each wire were not carefully placed and pressed down into position as it is wound into the slot.

There should also be prepared some small half-round wooden wedges. These are to insert in the slots of each

of the coils as they are wound in order to keep the outside end of the wire from getting loose and coming out of the slot.

Four are all that are required as there can never be a greater number of loose ends, as the operator will readily see.

The best means of holding the armature for winding is in the lathe, as shown in Fig. 46. The commutator end of the shaft is gripped in the jaws of the chuck, and

FIG. 45.—Tool for Placing Armature Wires.

the other end of the shaft is supported by the back center of the lathe.

The operator is standing in front of the lathe and the picture is made from behind the machine.

The belt should be removed from the lathe and the left hand used to rotate the lathe spindle and armature forward and back a half revolution at the same time that the wire is passed across the end of the armature from one slot to another.

The right hand is used to manipulate the wire and keep it taut.

As the wire is laid into the slots the hardwood piece, Fig. 45, is to be used with the left hand to straighten and press the wire into position while it is held firmly with the right hand.

Because of its small size it is possible, of course, to

hold this armature in the hands while being wound, but it cannot be as readily done, nor with as good results, as when mounted in the lathe.

The wire to be used is the coil labeled "Armature." This should be wound onto a spool before the armature

winding is begun. No special apparatus for tension is required in this operation, this being applied with the hand as the wire is laid in place.

To begin a coil wrap the end of the wire around the shaft at the shoulder on the commutator end. This is to anchor the end and keep it in place while the coil is being wound.

Let us now suppose that Fig. 47 represents the armature and slots as we would see them if we look from the end of the shaft on which the commutator is to be placed. The slots are numbered from I to 8.

It will be found advisable to mark the armature in like manner before winding. This can readily be done on the fiber end punching, either with a pen or pencil.

8

о

3

5

FIG. 47.-Armature Slots Numbered.

There are to be sixteen

The first coil of wire wound on will pass through slot I and return through slot 5. turns of wire in the coil, and if these are carefully laid in place these two slots will be half filled when the coil is completed.

In crossing over the end of the armature from one slot to the opposite one, eight of the wires should cross on

one side of the shaft and an equal number on the other side. Be careful to do this with each coil, else the winding will be one-sided when finished and the armature will be out of balance in consequence.