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If one have a small milling device adapted to be held in the slide rest, this operation of cutting the segments apart can be very readily and correctly done. If no special appliance is available the segments must be sawed apart with a hack saw, holding the commutator firmly in the vise while so doing. In this operation there is great danger of the saw running to one side and indenting the face of the commutator unless the saw is carefully started.

In starting the cut hold the handle of the hack saw high, so that the first cut will be made on the edge of the commutator farthest from the operator, and gradually lower the hand to make the saw cut entirely across the commutator. Be sure that all the metal between each of the adjoining segments is entirely cut away. It is even advisable to cut a little into the fiber to make this point sure.

The next operation is to insert the mica. This is supplied in strips a little wider than the spaces to be filled.

Suppose we were to number the segments, 1, 2, 3, 4, etc. Remove segment No. 1 by taking out the screws, and take enough mica to fill one of the spaces full. Coat it with shellac on the outside and also between the sheets, if more than one thickness is required, after which it is stood on edge against the side of segment No. 8. Prepare a second filling of mica and place against segment No. 2. These fillings should be of sufficient thickness that when segment No. 1 is replaced it will require considerable effort to force it down into place. Replace the screws and while so doing hold down on the segment with a piece of hard wood to help force it into place and

relieve the screws, else the screw threads in the fiber core are liable to be stripped.

Remove segment No. 3 and repeat the above operation after which Nos. 5 and 7 are removed and duly replaced. This will have filled all the spaces between the eight segments with mica. The commutator should be allowed

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to dry thoroughly. If it can be left for several days the result will be very gratifying. If, however, the commutator is wanted at once it will have to be "baked." This does not necessarily mean that it should be subjected to a very high temperature, but something like 150 to 200 degrees. This is less than the heat of boiling water.

If the commutator is placed on the front of the shelf of the kitchen oven with the door partially open, a moderate fire will give all the heat required.

Several hours of this treatment will amply repay the constructor. After the process of baking the commutator should be allowed to cool that the shellac may be entirely hardened before the final operations are attempted. These consist of facing off the commutator and truing up the ends. The operation is shown in Fig. 24.

Place the commutator on the 1-inch arbor with the round-head screws toward the lathe head. With a sharp tool take a cut across the commutator face, cutting down the heads of the flat-head screws to form part of the commutator face. Continue the cut until the tool just grazes the edge of the round screw heads. This cut should be made with a very sharp tool and should be of only sufficient depth to true up the commutator face.

Face up both ends of the commutator and it is ready for use.

Between the round-head screws the mica will stand above the segments, as it cannot be turned down. This can be cut away with a knife, if desired, which will add to the finished appearance of the commutator.

CHAPTER VI

PULLEY

This casting is of brass and is turned in such a shape that it is applicable for use with either a flat or round belt.

The first operation is to chuck the casting in order to drill the hole for the shaft. The best manner of doing this is to chuck the casting by the rim as, while held in this position, it is possible to drill, bore, and ream the hole for the shaft; turn and finish the face of the pulley, and true up one end.

Fig. 25 shows the shape of the pulley.

Because of the small size of the hole for the shaft the drill must necessarily be started very carefully, else it may "run out" to such an extent that the small boring tool will not be able to finish it up true.

The drill should be the same as used for drilling the bearing, a No. 20 twist drill. As in drilling the bearing the drill must be very carefully started after the work has been accurately centered. The drill is placed against the back center. With the lathe in motion bring the drill forward very carefully.

Fig. 26 shows this operation.

After the hole for the shaft has been drilled use the small boring tool to true up the hole after which the 3/16-inch reamer is put through to make it the proper size.

When the hole for the shaft is finished a 3/16-inch arbor should be placed therein and the back center of the lathe brought up to support it. This will steady the pulley casting while it is being turned and finished. The use of the arbor is shown in Fig. 27. In this illustration. the turning and facing of the pulley has been completed

TAP & COUNTERSINK

FOR 4-4-36 FIL. HD. SCR.

FIG. 25.-Detail Drawings of Pulley.

and the lathe tool is set to turn the groove for the round belt.

To finish the turning of the pulley it can remain on the arbor, but this must be mounted between the lathe centers. The edge of the flange which was held in the chuck and the end of the pulley can then be finished.

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