Universal M-18 - Checking Commutator Wear

Staining or Burning of Commutator
1. Check to see if the commutator surface is stained or burnt.
2. If it is locally burnt, correct with fine sandpaper.
Checking Mica (Undercut)
1. Check to see if the mica has sunk below the allowable limit.
2. If it is below the allowable limit, correct with a saw blade. Since the correction produces burrs
on the corner of the segment, chamfering should be executed.
Reference value
Allowable limit
0.50
to 0.80 mm
0.0197 to 0.0315 in.
Less than 0.20 mm (0.0079 mm in.)
1. Bad
2. Good
3. Mica
4. Segment
5. Depth of Mica
162