640. What should be included in performing proper maintenance of a D.C. motor's commutator?

Proper D.C. motor commutator maintenance includes side-cutting the copper segments and undercutting the mica to ensure good brush contact and prevent shorting. These procedures maintain a clean, dry copper surface and prevent the brushes from contacting the mica insulation. Other actions, such as applying oil, varnish, or removing the natural brown film, are detrimental to commutator function.