ZOsdUTATION-SLIP RING AACEINES ONLY Satisfactory commutation can be maintained by periodic examination of the slip rings and brush rigging. aults detected in the early stages of formation can ususlly be corrected at Little loss of time or expense. The machine has been properly adjusted at the factory for successful operation. The brushholders have been properly aligned and the correct brush spacing established on the slip rings. If during the course of service or repairs, the commutation appears unsatisfactory and warrants immediate attention, the source of poor operation may be attributed to several causes. The connections should be ehecked to insure good electrical contact and the brushes replaced if they are worn dangerously short. Care should be exercised to use the came grade and size of carbon brush, as these characteristics were determined when the machine was designed and are important contributing factors for satisfactory operation. Rough or dirty slip rings represent the chief causes producing chattering and noise. It may be necessary to clean the rings with fine grain sandpaper applied to the surface with moderate pressure. The brushes must first be lifted from the ring surface, and if possible, the machine srould be driven without load to provide a constant rotation of the motor at normal speed. imery paper and emery cloth should never be used on a slip ring because emery is an electrical conductor and particles are likely to become imbedded in the mica insulation and cause short circuits. “hile sandpapering offers the most satisfactory method for removing dirt and small surface irregularities, it may become necessary to resurface slip rings which are badly out of true by grinding or turning with 3-39