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FOR MANAGERS AND OPERATORS 377
of the surface of the commutator; (5) brush holder set at the wrong angle; (6) high bar or insulation. The remedies are: (1) Stretch the spring, if it is a spiral spring, or if it is not a spiral spring, do whatever is needful to make the spring stronger, installing a new one, if necessary; (2) put in a new spring, and, since the fact that the old spring has lost its temper is evidence that the spring itself is carrying too much current, reinforce it with a current-carrying jumper; (3) the remedy is obvious: do whatever is needed to loosen .the brush; (4) use sand paper, as before described, until the brush fits the commutator surface; (5) straighten the holder; (6) see section f, further on.
There should, however, be only sufficient tension on the brush to insure its making good contact with the commutator. Be careful, therefore, and don't get your springs too strong. If you do there will be unnecessary wear both on the brush and the commutator, and this will to some extent add the element of mechanical heat generated by undue friction.
The reasons for the brush sticking in the holder are: (1) Dirt in the holder or on the brush; (2) brush not true; (3) hammer that rests on the brush (where this type of tension is used) not working true on the slot-end of the brush. The brush should slip freely in its holder, though not freely enough to allow of any considerable amount of play, and the hammer should be so adjusted that it lies true in the slot at the end of the brush. A brush which is not true may be evened up by tacking No. 1 sand paper on a perfectly flat surface and rubbing tihe brush thereon.
(e) Commutator worn too thin. If the commutator wears down too much, although it may wear evenly and appear to be in good condition, the brushes will spark in spite of everthing you may do, particularly when the machine is working at capacity. The reason might lie in the fact that since the segments are wedge shape, as they wear down they become narrower, thus allowing the brush to span more of the circumference of the commutator than was intended, or there might be a slight error in the setting of the brush holder, and this error becomes greater as the distance between the brush holder and the commutator increases. The only remedy is a new commutator, but the sparking may possibly be lessened somewhat by moving the brush holder closer to the commutator. This trouble appears at its worst in a series type machine.
(f) A high or low commutator segment. This fault may