Cleaning a Horn Commutator question

[Visiblepump]

Most threads mention cleaning the space between copper contact bars with a toothpick. Seems simple enough, however when I tried it, there is not a depressed groove between the copper contact bars. The phenolic resin comes up even to the top of the bars leaving no room for anything to accumulate. Is this normal or is that an indication that the commutator is overly worn? Thanks.

[JayJay]

Originally Posted by Visiblepump

Most threads mention cleaning the space between copper contact bars with a toothpick. Seems simple enough, however when I tried it, there is not a depressed groove between the copper contact bars. The phenolic resin comes up even to the top of the bars leaving no room for anything to accumulate. Is this normal or is that an indication that the commutator is overly worn? Thanks.

Back in the day I was taught to slightly undercut the resin between the commutator poles with a broken-off hacksaw blade. Having said that, if it works then it likely doesn't need attention.

JayJay

[Herb Concord Ca]

Try using a metal dental pick or something similar. Smooth the commutator edges if needed.

[Visiblepump]

I did reluctantly try a dental pick. It barely made a scratch. That is when I decided it wasn't dirt, grime or whatever, it was the phenolic resin. I'm beginning to think that if there is a depression between the copper contact bars, clean it out. If the phenolic resin height is equal to the copper contact bars maybe nothing needs to be done other than a very light sanding of the whole commutator.

Am I wrong? When there is no longer a gap between the a commutator copper contact bars does the phenolic resin need to be filed/cut down? The commutator is so small, I would be afraid to try it and I don't want to do it, if it isn't necessary.

[rotorwrench]

On some of these old series wound motor, a person has to be careful performing an undercut between commutator segments. I've seen segments delaminate from that resin which could ruin the armature. As long as the resin wears at the same rate as the commutator segments then I'd leave it alone. The armatures with mica between the segments are a different story. That stuff doesn't wear like a person might think. It would need to be undercut. If they do need cut down a bit then I would use a jewelers file and just barely groove it.

[Pilotdave]

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This is slightly off topic of the OP, but a Dremel spinning a small wire brush worked well to clean/polish my horn commutator. Done in just a few seconds.

[Visiblepump]

Thanks for all the responses.