How To Repair Armature Commutator

Jones Mrse1992 · Friday, December 24, 2021

Commutator bars broken, how to repair?

Commutator bars broken, how to repair?

Hello mates,
I�ve got the following issue, you can see on the follwing pictures how destroyed are the commutator bars on this motor armature.

The segments were inside plus a lot of brushes dust

So I was wondering if you guys know if people repair or if I could do it myself somehow-

Thanks a lot in advance
What you call destruction is called wear. Have you checked the spring tension on the brushes? Back it off.
Somebody else recently had the same issue. Search around on the forum for it. Only been a day or so since it was posted.
When you find that post the pictures show that the wear is twice as deep as in your pictures.
On light wear like yours I just turned the high parts down to level again.
The working life of the armature is near its end. Based on the photographs posted,
it was an economically produced item with no longevity built into it when it was manufactured.
Note the lack of slot wedges and slot insulation. The commutator shows signs of "brush hop"
indicating the surface is out of round in addition to having the deep groove formed by brush wear.
Most everything is repairable, but this item would require a brand new commutator,
and likely have to be re-wound because of the nature of what's involved in replacing the comm.

For what it's worth, one could attempt to chuck the device in a lathe and turn the commutator.
What you'll likely discover however is the integrity of the comm will be so compromised
after having removed the groove that it will not hold "roundness" and a failure will cascade
again in short time.

Replace the entire armature if one is available.

Or, replace the machine the armature came from.

John
Originally Posted by McDowell

Hello mates,

I�ve got the following issue, you can see on the follwing pictures how destroyed are the commutator bars on this motor armature.

The segments were inside plus a lot of brushes dust

So I was wondering if you guys know if people repair or if I could do it myself somehow-

Thanks a lot in advance

Day Job made new Copper armature bars over in the "Motor Shop" section. My side we made new armature shafts and repaired end-bells.
However.. the least-cost motor they DID that for was 600 VDC, 100 HP off a quatah-million-dollah continuous coal mining machine.

Even then? It was only done at all because with the mining machine down, coal AKA "money", was not being mined whilst a NEW motor - which would have been CHEAPER - had to wait a delivery lead time of several months.

You one is a consumable/disposable motor. It did its job. It has become "consumed".

No surpprise it is now time to dispose of it.

Just replace the fool thing and go do something more useful or important.
I'm not seeing a destroyed bar. From your pix, it looks like a bad case of wear that you might be able to clean up in the lathe and undercut the mica.
BTW that armature looks like something bog standard like for a blender, can opener, or hoover.
Originally Posted by digger doug

I'm not seeing a destroyed bar. From your pix, it looks like a bad case of wear that you might be able to clean up in the lathe and undercut the mica.

BTW that armature looks like something bog standard like for a blender, can opener, or hoover.

Velly intelesting obselevation, Doug.
Before all that went to China, "Lamb" usta dominate that field. And Grainger stocked their whole dam' range.

I did say "consumable?"
My dad used to spin and file the high down and when just at the wear but no filing on it would crocus cloth to just clean bright..then lower the mica to about .020 with a shaped hack saw blade (if the Mica was high)..I helped him do a few..likely get another 20 years out of a lightly used motor.
That high areas can even be made a tad lower but best to be just even, flat across.
Brushes rubbing on the higher un wore shoulder would make them bounce..when running smooth with no bouncing brushes last a long time.

likely take about 15 or 20 minuets..and another 10 to scrape the mice if it needed that.
good to put two drops of oil in the bearings.

Last edited by michiganbuck; 04-08-2020 at 02:49 PM.
In my opinion all that's needed is new brushes. The comm segments are still intact. Unless it's a high RPM motor where an out of round comm will cause the brushes to float, there's really nothing to be gained by turning the comm. No reason why it shouldn't run fine with new brushes until the comm gives outs.
New buushes trimmed more narrow would work ,,but not good idea
Originally Posted by ptsmith

In my opinion all that's needed is new brushes. The comm segments are still intact. Unless it's a high RPM motor where an out of round comm will cause the brushes to float, there's really nothing to be gained by turning the comm. No reason why it shouldn't run fine with new brushes until the comm gives outs.

It appears to be out of round hence the some of the segments are blackened.
Image three shows a completely missing segment of copper with only the underlying insulation showing . . . No amount of turning, lightening brush pressure, bla bla bla is going to replace a missing commutator bar.
Unless you know of a small motor repair shop that can do this economically, you will be hard pressed to repair for as cheap as replacing it with a comparable motor.

Buy new, adapt as needed, and go back to using your machine.
Set up up between centers and true the commutator. Undercut a bit. Either it will fall apart
because the copper is too thin, or it won't and you can run the motor a bit more.
This is a half hour job, you will learn by doing - one way or the other.
WHHJR liked this post
Originally Posted by motion guru

Image three shows a completely missing segment of copper with only the underlying insulation showing . . .

I looked at the pics and assumed that was carbon buildup/burn discoloration. But think you're right. If you look at the thickness of the tabs the wire connects to, it's not very thick, and that should be the thickness of the comm segments. You look at the depth of the groove and it appears deep enough to have worn completely through.
Motion says he see a missing bar.
I don't see that but see one that is black. I have seen black bars before..
Jim rozen is spot on but I would not take any off the brush area just clean it up and to a high surface finish. That is my dad and I would do that part with fine crocus cloth.
Dad was journeyman elevator mechanic/ repairman and worked with DC motors that were bigger than a car. He knew his stuff about DC, 3 phase and singe phase.
Rust me on just clean up the com ..I have done this and made motors run like new

QT PT:[ it appears deep enough to have worn completely through.]]
If so that would be bad but I think it is just black ..you can give it a little rub with sand paper to it cone back to the right color..if it doesn't then agree a motor shot.

In a pinch(Not the best way)you can bump the brushes on a bench grinder to narrow the width about 1/6 high so the brush width touching the com is missing about .030 on two (the width way)sides,
this with also a hand polishing with sand paper.
Again the motor should run like new but the brush life would be shortened a little.
Originally Posted by McDowell

McDowell, rub some fine steel wool over the copper segments (especially the carbon fouled one) and attach a new picture.
Anyone care to get fitted with glasses...
Just for evaluation: micrometer check the high place and the low (center area), it looks like about .025 a side or so from hear so about .050 total ..I have repaired a number of brush motors that bad.
Some worse than yours with the mica high and so making the brush skip right over a pad.The mica should be .005 to about .030 below the major surface diameter. It is not uncommon to turn black with skipping..the bumping at width can also make them skip.

*The bush motor from day one is wearing away there....when it gets like yours and the brushes start bouncing for bumping the sides the com and the brushes wear faster.
Originally Posted by McDowell

Interesting that the grooves cut for balancing do not show any corrosion like what's accumulated on the outside of the laminations.
Originally Posted by jim rozen

This is a half hour job, you will learn by doing - one way or the other.

Twenty nine minutes for set up. One minute for machining.
Assuming the comm isn't worn out, I think you guys are way over thinking this. Guys put new brushes in, for example, Dewalt miter boxes, *all* the time, without doing anymore than unscrewing the brush caps, taking the old brushes out and installing new ones. I've done myself a time or two and they run like new.