Test Prods

illus. 90

testing armature for "ground"

illus. 92 testing armature for "open"

illus. 90

testing armature for "ground"

illus. 92 testing armature for "open"

Turning Down Commutator

If commutator is found worn and irregular, it should be turned down in a lathe and smoothed with No. 00 sandpaper. When turning, mount armature shaft on its bearing seats; do not mdunt on shaft centers.

Undercutting Commutator

After commutator has been turned down, the mica insulation between segments must be undercut to a depth of approximately .025". Unless mica is properly undercut, brushes will not seat firmly against commutator segments and generator output will not be normal. Also, there will be excessive arcing at brushes.

Undercutting is usually done with a special undercutting machine. However, if such a machine is not available, it can be done as shown in Illus. 93.

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