Abstract: Removing some of the insulating material between commutator bars of flat or cylindrical commutators, hereinafter referred to as "undercutting, " by exposing the commutator surface to one or more energy beams of a frequency and an energy level and for a time which are sufficient for removing the dielectric material to the desired degree without or substantially without removal of commutator bar material. The energy beam or beams may be arranged under an angle with respect to the perpendicular direction so that a certain amount of dielectric material is also removed from a zone underneath the edges of the commutator bars. A preferred high energy source is the CO.sub.2 laser. Preferably, the high energy beam is guided over the commutator surface to sequentially illuminate, e.g., by a scanning motion, at least all exposed dielectric surfaces.