Set the armature up in the lathe and run it at a relatively high speed. Don't run it fast enough to throw the windings out of the slots in the armature- - - -300 RPM or so should be good. Take shallow cuts with a sharp tool bit, and don't crowd the cut. Copper will machine pretty well, but it's prone to hang up and gouge if you take too deep a cut. In 50+ years of being around starter and generator rebuilding, I don't think I've ever seen a professional rebuilder undercut mica on a starter armature. It's done all the time on generators, and yes, it is necessary when soft carbon brushes are involved. (generators) As a final operation, polish the surface of the machined commutator with 100 grit sandpaper (never emery cloth- - -it's got metallic abrasives that will contaminate the surface.)
Jerry
Last edited by Hotrod Lincoln; 03/16/2010 3:25 PM.
