I've seen other images of Ametek motors that have them.  What purpose do they serve? It's hard to tell how deep they are. I have to think they would make the brushes wear unevenly.

Clearly they're there for a reason, but I have no idea why. We have so much combined knowledge here that someone must know. Thanks.

Joel

I'm adding this to the thread because both questions have to do with motor design and construction.

I know there are exceptions, but it seems like most vacuum motors today have double ball bearings. Is that because they run at such high speeds compared to yesterday's motors, and a sleeve bearing wouldn't last?

Joel

It makes sense though. Under high magnification it appears the brushes indeed are grooved. I appreciate your reply.

Joel