Abstract: Grooves in an article such as a commutator are filled with a soft brittle material before a grooved surface of the article is cut. With the grooves thus filled, the cutting is performed continuously and smoothly without involving formation of burrs projecting into the groove. The soft brittle material includes a water soluble material which can easily be removed from the grooves by merely immersing the article in water. Preferably, the soft brittle material comprises a sublimable material which is self-vanishing or disappearing as it undergoes sublimation to the vapor state when it is left to stand in the atmosphere.

Abstract: An improved commutator for an electric motor and a method of making the same wherein the outer surface of a commutator sleeve molded of a synthetic resin is coated with an insulating coating layer of an electrically insulating coating material. The molded commutator sleeve thus coated is protected from oxidative degradation and cracking which would otherwise result in removal of a commutator bar and insulation failure.

Abstract: A rotor for printed-wiring motors includes a flat disk-like non-iron armature mounted on a hub secured to a rotating shaft, the armature being composed of at least two sheet coil assemblies bonded together under heat and pressure with a first thin insulating disc disposed therebetween. Each of the sheet coil assemblies is composed of a pair of sheet coils bonded together under heat and pressure with a second thin insulating disc disposed therebetween. Both the first and second insulating disc are formed of a web of aramid fiber coated with an insulating bonded adhesive.

Abstract: Grooves in an article such as a commutator are filled with a soft brittle material before a grooved surface of the article is cut. With the grooves thus filled, the cutting is performed continuously and smoothly without involving formation of burrs projecting into the groove. The soft brittle material includes a water soluble material which can easily be removed from the grooves by merely immersing the article in water. Preferably, the soft brittle material comprises a sublimable material which is self-vanishing or disappearing as it undergoes sublimation to the vapor state when it is left to stand in the atmosphere.