# how do I turn the Comm?



## bipole (Sep 8, 2009)

I just picked up a GE 11" series forklift motor at my local forklift salvage/repair yard (no, he doesn't have any more, I've been bugging him for over 6 months). The commutator definitely needs turned and I have access to a lathe and a mill. The lathe has a 14" swing with a 4-jaw chuck and a live center and i have a basic competency of it's operation. The rotor shaft has pilots holes on both ends.

I'd like to turn the comm myself but havn't found a whole lot of info on the web specific to the cutting portion of the process, though I have found a bit on dealing with the mica slots after turning. One source (IH farm equipment forum) stated to take no more than .005" per cut but didn't state if that was off the radius or diameter.

Any help is greatly appreciated.


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## major (Apr 4, 2008)

bipole said:


> I just picked up a GE 11" series forklift motor at my local forklift salvage/repair yard (no, he doesn't have any more, I've been bugging him for over 6 months). The commutator definitely needs turned and I have access to a lathe and a mill. The lathe has a 14" swing with a 4-jaw chuck and a live center and i have a basic competency of it's operation. The rotor shaft has pilots holes on both ends.
> 
> I'd like to turn the comm myself but havn't found a whole lot of info on the web specific to the cutting portion of the process, though I have found a bit on dealing with the mica slots after turning. One source (IH farm equipment forum) stated to take no more than .005" per cut but didn't state if that was off the radius or diameter.
> 
> Any help is greatly appreciated.


Hi bip,

And why does the comm need turned? TIR? Raised bar? Grooved? Pitted?

But if you're turning it, error on the safe side. Take as little as you can off each pass. Afterall, a few extra passes don't take that much time. And you want to get a good finish on your final pass. I don't recall the spec. There should be such info out on the web. Tonight I'll see if I can spot something in one of my commutator or brush books.

major


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## few2many (Jun 23, 2009)

How about if you just spun it by hand and held some emory cloth or a light file against it? This would remove scratches and clean up the suface contact area without removing hardly any metal.
Hopefully, if I'm wrong with this logic, someone will chime in before either of us ever do it!


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## TheSGC (Nov 15, 2007)

That comm looks fine to me, it just needs the motor to be spun on 12 volts for an hour or two. The brushes should clean up the comm with some rotating, at least it did for the past two ADC motors I have used.


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## bipole (Sep 8, 2009)

The comm has some moderate pitting. In the lower left of the pic on the comm there is two dark spots that are deposits of copper above the surface next to a pit of about the same volume. Don't know how it got displaced but it looks like the whole comm had some arcs and sparks going on for a while.

The whole motor looks very crusty right now but she'll be a real gem when I get through with her. She's out of an Allis Chalmers E50.

Here's a pic of the carcass and the crustiness.


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## major (Apr 4, 2008)

bipole said:


> The comm has some moderate pitting.


O.K. bip,

Nice to have motor talk here and not crap about air or batteries.

From my old Morganite Electrical Carbon Limited book, 1978. No modern library # I can see.:

Rough Turning:

Tungsten Carbide. 100 to 750 ft/min cutting spd, 0.002 to 0.005 in/rev rate of feed, 0.0025 to 0.020 inch depth of cut.

Finish Turning:

Tungsten Carbide or Diamond. 100 to 1200 ft/min cutting spd, 0.002 to 0.005 in/rev rate of feed, 0.0005 to 0.005 inch depth of cut.

Also it says quote:

The highly polished - almost burnished - finish that diamond turning can produce is not an ideal surface for brush operation. If such mirror finish is obtained it should be broken with 100 grit silicon carbide abrasive cloth or similar abrading medium:* but do not use emery cloth*.

Hope that helps,

major


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## bipole (Sep 8, 2009)

Major, that's exactly what i needed. Wow, thanks!

I just checked McMaster-Carr for tungsten carbide- no joy. The diamond bits are pricey. I've got their C-2 carbide tipped cutting tool for cast iron and non-ferrous metals, I'll give that a try on a light cut and see if it does the trick.

It'll be another week untill I've got some machine shop time. I will be able to disassemble and bead blast the hard parts in the next day or two. I'll get some progress pics along the way.




major said:


> O.K. bip,
> 
> Nice to have motor talk here and not crap about air or batteries.
> 
> ...


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## Guest (Apr 15, 2010)

Turning should be the last resort. If you do turn the com take very very little off at a time. This is copper which is fairly soft. If you cut to deep on a pass there is a good chance of digging in and making a gouge or bending the bars. If the brushes do not move up and down when you spin the motor Then chances are the com is OK. Put your fingers on the brushes while spinning the shaft by hand. If there are any bumps or out of round you will feel it. A dial indicator would also be helpful. If everything checks out then give it a light polishing with a good grade fine emery paper. Make sure the dust and dirt is cleaned out of the spaces between the bars. If insolation is missing replace it with the proper material. Take no short cuts. For example. Years ago when I was first building my EV and messing with old motors trying to save some money someone told me J B weld was a quick and easy way to fill in between the com bars. J B weld is not a good insolator. Needless to say that was a real mess to fix. What I am trying to get across is take your time and don't be afraid to spend a couple extra bucks to do it right the first time. I have found it usualy saves money in the long run.


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## Guest (Apr 15, 2010)

I said to use emery clothe but that was wrong. Emery looses grit that can cause more problems. Silicone carbid is better.


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## bipole (Sep 8, 2009)

Thanks Wizard, all good stuff.

Here's a few pics of the 9" GE I'm just finishing up. Its from a Hyster p/n 339128.

I managed to turn off the big flange on the DE and get a standard 9" adc/warp front on her (4" pilot, 8.4" bolt circle). I put a standard 8" pattern on the rear just because it would fit.

I may sell this one if the 11" works out good.


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## DIGGER11 (Mar 16, 2010)

major said:


> O.K. bip,
> stuff deleted.....
> 
> The highly polished - almost burnished - finish that diamond turning can produce is not an ideal surface for brush operation. If such mirror finish is obtained it should be broken with 100 grit silicon carbide abrasive cloth or similar abrading medium:* but do not use emery cloth*.
> ...


I did a course on rebuilding Electric Motors back in 1980 and we were taught to polish up the armature with Emery Cloth. This was after undercutting the armature with a broken off hacksaw blade.
I was working for the Federal Government at the time and the Soldering course we did was called "High Reliability Hand Soldering" and it was designed for the Apollo missions - so I am surprised that their course on Electric Motors was wrong.


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## major (Apr 4, 2008)

DIGGER11 said:


> I did a course on rebuilding Electric Motors back in 1980 and we were taught to polish up the armature with Emery Cloth.


Hi DIG,

I was quoting the book. A 1978 edition. Original compiled in 1923. 

Morgan cut its first electrical brush from graphite early in 1903. Because carbon gives a long life and will not weld, carbon brushes quickly replaced their copper predecessors and a new technology was born. 

From http://www.morganite.com/ 

So they've been in the motor brush business for 107 years. What do they know 

When you're working for the government (or anybody), you do what you're told.

Cheers,

major


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