cutting the comm

[trw]

i dont have a machine to cut a comm because i cant afford and i wont be able to afford for a looong time. is there any other way to cut a comm like using sand paper or something? i know using a brush with metal bristles will leave it to rough and and just tear my brushes up. Will fine sand paper work? If not what else can i do?

[Grizzbob]

To make the comm perfectly round again(which is the point of using a lathe), no, there really isn't any other good way. You can make a comm look nice & shiny with sandpaper, but that doesn't make it true again, so the brushes will still bounce on it when you run it(which is what accelerates wear on both brushes & the comm).....:cool:

[MachWon]

It's got to help a bit doesn't it? Say, placing the armature in a Dremel, or small drill, and then saddling it in very, very fine grade sandpaper for a moment or two. Then doing due diligence and clean out the spaces etc.

Theoretically it should come out more round and certainly smoother. My guess is better than not doing anything at all.

I'd love to hear of someone that has a good dyno try this as an experiment sometime.. Test the motor with a rough com, then test it sanded, then test it after a cut.

Has to make some sort of difference :)

I imagine the biggest problem would be sanding it right.. too much pressure on one side of the sandpaper could make a cone of it.

[filipinoguy]

Check to see If your LHS cuts comms. My hobby shop charges 5 bucks for it.

[trw]

well i tried the sand paper theory. i lightly sanded the comm until it was shiny. I also sanded the brushes since i figured if i did that by runing the motor at full throttle would smoothen out both surfaces and well it wored. i sand both brushes and comm put the motor back together and turned the car on. i ran the motor half throttle forward and half throttle backwards for like 8 seconds each direction and that like 1 mississippi 2 mississippi etc... took it back apart and the comm and the brushes were smooth agian. But the comm wasnt as smooth as it was..dont get me wrong its pretty smooth but not as smooth as it was...i dunno the outcome of this expirement yet cause i cant drive my car until my adjustable tunrbuckles come which should bethis late afternoon. I'll run my car i will charge my battery up to the voltage i normally charge it up to for a normal drive, i will time the battery, i will watch its accelertion basicly ill keep a close eye on it and ill post results.

[highroller]

Using sandpaper whether done in the motor or taken (leaves more room for and uneven surface). You are bound to end up with uneven areas, and with high reving motors just a thousandths can cause big problems. What looks good to the eye may not be. I tried it many, many years ago before lathes were introduced and motor never ran as good (cutting a strip the size of hood and feeding it thru - turn shaft 5-10 times evenly, thinking/assuming the surface would be even). The motor was put away and never used (Reedy Pink Dot). Trued it when I got my lathe and tested on dyno (LaVco) re run test showed unsteady power - meaning brush not broken in, poor conductivity RPM down compared to the other 4 Pink Dots. After working on motor (truing, breakin) the numbers were as close to the others.

[TEM]

High performance = high maintanence! If you want the performance, you will HAVE to do the work. To keep it up; cutting on a lathe is mandatory. Sand paper might make the comm shiny but you are only kidding yourself. A com stick is for removing crud only.

If not, get a higher turn motor(ie stock or spec) and run low silver content brushes! That way your motor will take a beating and keep on ticking!

You got no choice but to comply. Otherwise; a motor that came fast will go slow quickly, and or may even die.

[trw]

the sand paper was only an expirement. I can always go lathe it or w/e if it doesnt work out.