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GENERATORS AND MOTORS 153
medium-weight canvas cut a piece about six inches square and fold it so that it forms a pad 6 inches long by two inches wide. Dampen and press down, so it will stay folded.
Open the pad and along the center section of the inside of the pad, apply a light coat of ordinary vaseline. Refold the pad and lay it aside for a day in a warm place, to give the vaseline time to soak through the fabric. After this the pad should be kept in a closed box where it will be free from dust and dirt. The pad may be recoated with vaseline from time to time whenever it requires it.
By holding it against the commutator for a few onds the commutator will receive all the lubrication it requires. If soft brushes are used apply no lubrication. as they contain sufficient paraffin for the purpose.
Commutator Conditions
Reduce sparking to an absolute minimum. I There should be little or none unless the machine is overloaded. If there is sparking and the machine is not overloaded, proceed at once to ascertain its cause.
(82) The easily discoverable causes are as follows: brushes improperly set; wrong brush pressure; poor brush contact; high commutator bar; improper brushes purchased for replacement; commutator out of round: commutator dirty ; high mica.
Make sure that combined oil and carbon dust has not formed a short between the bars or formed a spot of semi-insulation on the commutator face. Be sure th< commutator has no high bars and that it is perfectlyround— either of these faults can be tested for easily.
(83) High bars may be detected ordinarily by a slight clicking sound when the machine is run at moderate speed, which can be accomplished without load by manipulation of the switch. There can be also a low bar or bars, in which case the brush would ride inward slightly as the armature is rotated slowly by hand. If the commutator is out of round, that fact may be made evident by rotating the armature slowly by hand.