I came by a beautiful DC motor, 10 HP and 1750 RPM, a nice collector’s item if you like. It weighs maybe about 300 lbs and has a heavy cast iron frame and a 1 5/8 inch shaft. It probably has about 5 or 10 years service on it and is greasy and dusty but otherwise in nice shape.
The problem is that the commutator is damaged. Under the brushes, it is depressed perhaps as much as 1/16", and visibly a little rough. The brushes are at four positions around the circumference at 90 degree angles (there are four poles in the stator). At each position there are two brushes in parallel. It looks like one of the brushes somewhere might have worn down through the carbon and brought some metal into contact with the commutator. There’s also a fine sparkly coating of copper dust in the region.
Can I repair this? Can I smooth it with successively finer sandpaper? Should I pull the rotor out and turn the commutator on a lathe? How deep can I go? Can I tell how deep I can go by looking at the end face of the commutator to see how thick the little copper segments are?
What I would like to do with the motor is clean it up and maybe play with it a little, do some experiments, that sort of thing. I don’t need to recondition it for heavy service and sell it with a guarantee.