Armature Inspection & Test

Inspect armature for wear or damage due to contact with field coil magnets. See Fig 1 .
A dirty or burnt commutator surface may be resurfaced with emery cloth or a lathe within the following specifications. See Fig 2 and Fig 3 .
If commutator runout and diameter are within limits, check commutator for damage or for carbon dust or brass chips between segments.
If surface is dirty, recondition it with a #500 or #600 sandpaper. Then, check mica depth. If necessary, undercut mica with a hacksaw blade to achieve proper depth. See Fig 4 .

Fig 1: Identifying Armature
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Fig 2: Measuring Commutator Diameter
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Fig 3: Measuring Commutator Runout
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Fig 4: Measuring Commutator Mica Depth
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Check for continuity between each segment of commutator. If an open circuit exists between any segment, replace armature. See Fig 5 .
Place armature on an armature tester. Hold a hacksaw blade on armature core. See Fig 6 . If blade is attracted to core or vibrates while core is turned, armature is shorted. replace armature.
With ohmmeter, check that no continuity exists between commutator and armature coil core, and between commutator and armature shaft. If continuity exists, replace armature. See Fig 7 .

Fig 5: Identifying Commutator Segment

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Fig 6: Testing Armature

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Fig 7: Identifying Armature Components

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