Cutting comms?

[old phart]

I just got a Cobra comm lathe. It says that .275" is the minimum for a comm. What happens if you cut one to say, .270"? Or even .260"?

Or, if you clean up a comm and it mic's out at .275" is it still usable? Just can't cut it again after the next set of brushes?

Thank you! :D

[tc3guy]

You shouldnt cut your comm past .275 becuase it will be to thin and fly apart and will be a big mess. You'll also get hurt in the process. I have never done this but I read on this board along time ago about some on who did. They got there eyes scraped up real bad.

[racerman333]

well i just keep cutting it until it really looks like i should stop using it, i dont have a caliper so its almost impossible to tell when to toss it out.

[Grizzbob]

Actually, I have cut some of my comms down just under .270", but it's not a good idea to go that far. When you get it down in that range, your motor is already getting to a point where it won't perform as well anymore(due to there not being enough copper left on the comm to conduct electricity as well), & if you continue to cut it you'll eventually completely run out of copper there, which could end up damaging your lathe bit(as well as yourself, possibly). So, if you're really getting close, then now would be a good time to order a replacement armature for that motor.... :)

[Car_Head12]

***? i think my brother wrote that, no idea. sry about that. hew being a real sh|t head tonight

[ 08-17-2001: Message edited by: Car_Head12 ]

[old phart]

Thanks for the info Grizz! FYI, I just cut a buddies comm. It mic'd out at .280" It was a Retro series motor. He put it back together, and installed it in his Rustler. Half throttle he said the tires got skinny. He rapped it to full throttle, and the windings exploded, came off the armature and jammed up inside the magnets. That was not from cutting too thin was it? I think it was because he had such a good comm for a change :D

[Grizzbob]

No, I doubt the comm cut had anything to do with it. That is one drawback to buying machine wound motors(like the Retro series), they can be subject to little flaws in the windings, which can make them blow at any given time(I believe that also has something to do with all the stock motors that've been blowing up lately). With machine-wounds, you have a chance of getting a real sweetie, or getting a timebomb, & it's hard to tell them apart. That's one big reason why I stick to hand wound motors myself, you almost never hear of them blowng a wind, because the guys who wound it did it very meticulously(if they did it right) & made sure it would hold up well, as well as perfom strong. I'm a firm believer in doing things by hand(whenever possible), I do it a lot at work, & the workmanship really shows........ :)

[Railman]

I have found that at least with stockers you can USUALLY go to .270 without any problem. We however use carbide tooling & don't have to worry about the com flakeing & destroying the diamond tip. On some small ones we've had them cut cleanly only to have them flake off in a race. Like Grizz said sometimes they will go below .270 but it's pretty risky to run those. Just my $.02 ;)