Tell me about Commutator Stones

[Randybee1]

Hey guys,  I have a Onan Generator head that has some pretty ugly looking slip rings. I want to buy a comm stone to clean them but know nothing about them. Other than coming in course, medium and fine are all stones the same? Is there a difference in quality in the cheap ones as opposed to the expensive ones?

Thanks, Randy B

[DanG]

Clear photos of the condition of the rings would be most helpful.

Usually commutators and slip rings are best left alone - use an electrical high-dielectric solvent to chase grease and oil off, blot the last puddling of solvent off the bottom edges and solvent wipe that then dry and then leave it alone unless you are seeing way mutant brush wear or the edges getting chipped.

Brushes ride on a layer of ionized gas made up of brush material and commutator metal that gets redeposited back to the metal surface repeatedly. You can chew through a lot of a brush set(s) trying to get that film back, back to the point there is nearly zero friction and brush wear.

If you decide to use a stone it's not a thing to be done by hand alone - have a tool rest similar to a lathe and sweep it laterally with featherweight pressure, let the RPM's do the work. Also its not a good idea to do this on an energized circuit, the wind-down RPM's on a balanced motor often are enough.

[WStayton]

Hi Guys!

DanG:

  That's one of the things that I love about this forum - there just is NO substitute for getting the information from somebody who has been-there-and-done-that!

  Reading about it in a book is nice, but the book doesn't necessarily put the emphasis on what is MOST important like somebody who has done it, and, just maybe, s#$%^&d it up the first time!  <grin> (Raises hand, sheepishly!)

  I have never done the brushes on a big gnerator, but the brushes on an old style, before-alternators, automotive generator are essentialy the same thing, though they run on the commutator not on slip rings.  I carefully (well, carefully for ME) cleaned up the brush area for the generator for my 1952 Brockway school bus and I made such a mess out of it that I needed a new set of brushes about once a week for six months before things wore smoth and got cleaned up!  Lesson learned:  Don't fix it unless it is absolutley broken!

  My two cents which aren't even worth two cents!  <grin>

Regardz,

Wayne Stayton

[Tom Reed]

I just can't resist. If you get good at this process, does that make you a stoner???

[vdubnut62]

I just can't resist. If you get good at this process, does that make you a stoner???

Oh pu-lease!
Ron

[rcavictim]

I just can't resist. If you get good at this process, does that make you a stoner???

Finely honing your humor I see! 

[DanG]

Whetstoners you all are.

I forgot to mention *if* you have to use a commutator stone the finish step...

If you can't get fabric backed sandpaper in pre-cut 3/4" etc. thick rolls then any canvas, leather or nylon webbing with a matching strip of wet-dry paper to loop around the commutator and then  polish with push-pull 'belt' saw motion. Dry dress it with strips of 220 or 320 and polish with 400-800 and solvent clean afterward.

Some say emery cloth may cause shorting as the corundum (aluminium oxide) can be mixed with iron-bearing stone like magnetite so its fabric-backed anything else...

[Randybee1]

Well, I bought some stones. I have no idea as to the quality, but I "stoned" my rings and they look great. Next problem for me is to figure out why one leg gives me 120 V and the other 62V.. more diagnostics!

Randy B