Bench Testing: Commutator

Inspect commutator for roughness, grooves, burns or pitting. If necessary, sand lightly with 500-600 grit sandpaper. Check commutator for out-of-round. Check mica insulators undercut. Ensure depth of undercut is .020-.031" (.50-.80 mm). Commutator may be turned a maximum of .04" (1.0 mm) from original size and mica undercut. Replace if excessively worn.