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502 HANDBOOK OF PROJECTION FOR
GENERAL INSTRUCTION NO. 7— CARE OF THE COMMUTATOR.— The commutator of a D. C. motor or generator should require very little attention, but sometimes it does require a great deal.
The best evidence that the commutator is in first-class condition is a sort of glazed appearance, smooth as glass, a rather dark brownish shade in color, and a slight squeak from the carbon brushes when the armature is revolved slowly. To obtain and maintain this condition the following care is essential :
(a) Brushes, set as nearly as possible at the sparkless point, which point may, with the old style generator lacking the inter or "commutator" pole, vary with the load. On the newer type generator the inter or commutating pole is used, and the manufacturer marks the point at which the brush yoke should be set by making either a chisel or a centerpunch mark on the yoke and on the frame. Some manufacturers fill these marks with white paint so that they are very easily seen; some do not. If these marks are present the brush yoke should always be set so that the marks on the frame casting and on the yoke coincide or, in other words, are opposite each other.
(b) The brushes must have sufficient tension to make good electrical contact with the commutator, remembering that every particle of unnecessary pressure will tend to unduly wear both commutator and brushes.
(c) The commutator should be kept clean and free from dust. This may best be accomplished by cleaning the whole machine every day, blowing the dust out from around the field poles, etc., with a bellows, and last of all, wiping off the commutator with a canvas pad made as follows :
Cut a piece of ordinary canvas 6 inches square. Fold same so it is 2 inches wide by 6 inches long, which will form a pad with a face of one thickness, backed by two thicknesses. Next open up the pad and smear a little vaseline on the center section, which is the back side of the face of the pad, after which refold and let lie a few hours in a warm place, whereupon it is ready for use.
Sufficient vaseline will gradually soak through the canvas to give the commutator all the lubrication it needs, which is very little. The foregoing holds good in summer, and in winter, too, if the generator is located in a warm room. If, however, the machine is cold, then it will be well to moisten the face of the pad by using a few drops of a very thin oil on a piece of glass, spreading it around evenly and then wiping