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screw head the surplus ends should be cut off close to the

screw.

These wires which run from the slots to the segments should be thoroughly shellacked, after being connected, to prevent the insulation from loosening and fraying out when the armature is in use.

When this shellac is dry the armature is ready to assemble in the machine.

Do not attempt to run the machine until the shellac is entirely dry, or the centrifugal force, when the armature is revolving at high speed, will cause the wet shellac to fly off and the outside wires of the coil may lift from the slots and be damaged or broken by coming in contact with the field pieces.

FIELD WINDING

When this operation is reached the advantage of the alternate long and short pole pieces will be apparent.

The assembled field can be separated and each of the halves alternately mounted in the lathe for winding.

When held in this manner the wire can be very readily spooled on.

Before winding the coils the sharp corners of the field should be very slightly rounded to guard against the cutting of the insulation on the wire, after which the iron should be covered with one or two thicknesses of stiff paper secured with shellac.

Paper should also be attached to the inside surfaces of the field washers.

In order to make a neat appearance in the winding of the coils it is necessary to keep an even tension on the wire while it is being wound.

An easily constructed apparatus for this purpose is shown in Fig. 59. This consists of a piece of board about 18 inches in length, near one end of which is bored three -inch holes, I inch from center to center, and into these are set three-inch wood pins. At the opposite end of the board is set a pin to hold the spool of wire.

The wire passes around the pins as shown in the drawing. This will be found to give sufficient tension and leaves the hand free to guide the wire.

When in use this board should be located some distance away from the lathe, say three feet or more. In this case the wire will need very little manipulation to keep it winding evenly.

The wire as usually furnished with these dynamo parts is in coils, but it should be wound onto a spool before attempting to wind the field coils.

An excellent way to mount the field parts for winding is shown in Fig. 60.

An angle plate is attached to the face plate of the

WIRE

FIG. 59.-Tension for Field Wire.

lathe and on the shelf of this the half of the field is secured by means of the side-bearing rod.

The short end of this passes down through a hole in the angle plate shelf, and a nut and washer are attached to the side-bearing rod below.

The slots in the back of the angle plate allow it to be adjusted so that the field piece will swing evenly.

The back center of the lathe may be brought up against the field piece to help in steadying it, but this will not be absolutely necessary if the nut on the side-bearing rod is screwed up securely.

The winding on each of the halves of the field should be begun so that the inside ends of the wire will come

out on the upper end of the coil at the pulley side. The pulley side of the field is resting on the angle plate shelf in Fig. 60.

In winding, rotate the lathe backward, that is, so that the top of the face plate is turning away from the operator.

[graphic][merged small]

Twelve layers of No. 22 single cotton-covered wire should be wound on each coil.

Should the winding become uneven after two or three layers have been wound on, cut some strips of stiff paper just wide enough to fit between the field coil washers, and after shellacking one side wind one on over the top layer of wire to form a nice even surface on which to wind

the next layer of wire. One of these strips should be used whenever the wire becomes uneven.

The twelfth layer will bring the outer end of the wire at the top of the coil, and this should come out on the commutator side of the machine, as it is to be attached to one of the binding posts on the connection board.

Be sure to leave sufficiently long connections at both the outer and inner ends of the coils.

After completing the twelfth layer of the wire, wind on another strip of shellacked paper and over this wind a layer of hard twisted cord or fish line, which should be afterwards given a coat of shellac.

The outer layer of cord is for the protection of the wire. Both coils should be wound in the same direction, and after assembling the two parts of the field the two inner ends of the coils should be twisted together, and then touched with the soldering iron to make a good connection.

The outside ends of the coils are carried to the binding posts of the connection board and attached as shown in the diagram in the chapter on Connecting and Starting.

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