Page:Popular Science Monthly Volume 91.djvu/629

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Popular Science Monthly


��while the laminae are being turned. The armature is now ready to receive its wind- ing. Referring to Fig. 6, the method of wiring can be easily understood. There are two coils per slot, each having a span of six slots. The winding consists of twenty-two coils, each of which is composed of 20 ft. of No. 29-gage enameled wire. Now measure eleven 40-ft. lengths of wire and in the middle of each twist a loop about 1 in. long. Before beginning to wind the armature the slots must be lined with empire cloth. Cut from the cloth eleven strips 1% in. long and 1 in. wide and line each slot, using a little glue to hold them in place.

Beginning with slot No. 1, skip to slot No. 6 and wind until you come to the loop, which should be brought out on the side of the commutator. The next coil is wound in the same manner in slots No. 2 and No. 7, etc. Now to the end of the first coil (not the loop) twist the beginning of the second coil. It is well to tie a knot in the end of each coil for identification when the commutator connections are made. When the winding is complete it should be tested for grounds and breaks, etc. This may be easily accomplished by means of an incandescent lamp in series and the lighting circuit. If the coils pass the test, strips of fiber 1/16 in. thick, 5/32 in. wide, and 1^2 m - l° n g should be inserted in the slots above the wire to prevent the wire from being thrown out by centrifugal force. Now give the armature two coats of insulating varnish and set aside to dry.

We will now need a commutator. The writer has found by experience that this had best be purchased. It may be ob- tained from an electrical repair or supply shop for a small sum. It should have 22 segments and be of the dimensions given in Fig. 5 and fit snugly on the shaft. To connect the armature coils with the com- mutator proceed as follows: With a fine- toothed hack saw cut a nick about 1/16 in. deep in the end of each commutator bar on the side nearest the coils. Now solder the loops to alternate bars, keeping them in their proper order. Be sure to use a non-corrosive soldering flux. One element of the winding is in heavy lines, Fig. 6, clearly showing the proper connection of the loop to the commutator segment be- tween the bars connected with the begin- ning and end of the coil. When the connections are complete, center the arma- ture in a lathe and take a very light cut

��off the commutator, removing the super- fluous solder. On the opposite end of the shaft is a brass thrust sleeve, which should be a snug fit and be pressed on the shaft.

The top bearing and brush holder are shown in Fig. 7. The bearings are turned from a piece of brass or phosphor bronze rod. Both bearings are of the same dimen- sions. The brushes are of J^-in. square carbon, held in two pieces of square brass tubing. The tubing is sweated to an 8-32 brass screw 1 in. long and set at such an angle that the brush is at right angles to the commutator. Each brush holder is insulated from the bearing bracket by two fiber washers, one on each side of the bracket as shown in Fig. 7. Now clamp the bearing bracket, field laminae, and hard wood ring, Fig. 8, rigidly together by means of the two }i-in. bolts, which should be cut off to 2% in.

The lower bearing is to be set in the center of the top of the fan case and secured by means of two small brass screws. A small brass oil tube about 1 3^ in. long is soldered to the oil hole in the bearing and brought out through a hole in the hardwood ring. On the underside of the bearing is a dust cap, which consists of a felt washer 1 in. in diameter covered by a cap about 1% in. in diameter. The top of a small paper fastener will, serve the purpose well. The dust cap is on the underside of the top of the fan case. The connections are shown in Fig. 9.

The motor is now complete and should be tested out. If it runs in an anti-clock- wise direction the field leads must be re- versed so that the armature will rotate in a clockwise direction.

( To be continued)

��Connecting a Spotlight in an Automobile Dynamo Circuit

A SPOTLIGHT was wanted on an auto- mobile in which the lights were on a series circuit. As the spotlight was only to be used occasionally the method of wiring was as follows: A single switch was mounted on the dash and a wire connected with it from the left hand termi- nal on the back of the ammeter. Another wire from the switch was connected with the spot lamp and grounded to the other terminal of the spot lamp. If a spot lamp is procured with a switch on it, it is only necessary to connect a wire from the am- meter to the lamp and ground the lamp.

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