Concentric Running
Commutator and Slip Rings must have perfect concentric running. If this is not the case the brushes will lift off from the contact surface area with the result of excessive sparking. This leads to pitting and consequent damage to slip ring or commutator surface. Smaller distortions can be rectified by hand with the help of commutator grindstones. However, if the distortion is excessive the Commutator or Slip Ring has to be machined or ground off in its own bearings, if possible at full speed.
