Reconditioning commutator issues in constant duty motor 1

[fastline12]

I will have to first admit that we did not turn the commutator in the lathe due to complications with fixturing. We elected to use a careful hand file followed by sanding and scotchbrite. The brushes are under a lot of pressure by the springs. It was pretty evident turning the motor by hand that it was a bit noisy. We decided to fire the motor at half voltage to test. It ran for a total of maybe 20sec. There is already evidence of chipped brushes.


Obviously we need to refine this process and redo our work. I noticed the air gaps between bars are not filled with mica and the question was raised if we shold try to fill with an epoxy to improve brush life?

Also, regarding reconditioning the commutator, I assume turning is really the only way to do this right? if that is the case, should the bars receive a .001-.005" chamfer on the corners? Or should we consider a fill to smooth things out?

 

[Skogsgurra]

This learning experience may turn out costly. Leave the machine to a winder shop. They know how to do it.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[electricpete]

I agree with Gunnar, there no substitute for experience. Commutators and brushes are special beasts that require TLC.

Still, I'll give you my take on your questions with the caveat that I have not done the work myself but read about it. Maybe others will chime in with other comments or references.

Obviously we need to refine this process and redo our work. I noticed the air gaps between bars are not filled with mica and the question was raised if we shold try to fill with an epoxy to improve brush life?

My understanding: No, do not fill in the gap. Providing a smooth surface with no gap would encourage tracking. The mica between segments should be undercut to a depth approximately equal to the distance between segments.

Also, I believe it is good practice to do a manual run-in to seat the brushes as follows: put emery cloth on the commutator and manually rotate the brushes over that sandpaper.


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(2B)+(2B)' ?

 

[fastline12]

I guess the guys did not apply any chamfer to the bars so I went ahead and did that. She is 100% better now. The sound is normal and turning by hand, it does not catch or feel abnormal. I am hoping the bedding process will get it the rest of the way.

 

[dArsonval]

Normally a commutator is turned while the machine is dismantled.
Larger equipment presents a different set of circumstances.

The URL below may help give you a better "visual" as to the process
or sequence-of-repair relating to a D.C. Electric Motor Armature.
The photos do not show the polishing sequence or the chamfering of the bars
after the commutator is turned. Nor is there a photo of the required bar-to-bar testing
of the item after turning, to ensure no small pieces of copper have shorted any bars together.

http://www.pbase.com/visual_first/turning_armature_commutator

The armature shown in the group of photos did not require "undercutting" so that sequence
of the repair in this case, is also omitted.

A note related to the use of emery cloth. An abrasive paper referred to as "Garnet Paper"
is used to sand the commutator after turning. In a pinch, emery cloth could be used but is
frowned upon within the repairing of commutators because it has metal particles in it.

Always enjoying the forum,
John

 

[electricpete]

Good info John. Thanks for pointing out the Garnet paper.

=====================================
(2B)+(2B)' ?

 

[fastline12]

Thanks for the replies. I am also a machinist so the turning of the commutator did not really throw concern but there was issue in getting all the PTO side gear off the motor without replacements available.

The commutator was sanded but not with brush pressure because the brushes push with such force that you could not get paper under them without damage. Actually I have never loaded brushes that were such a PITA!! Things are tight in there and those brushes gots some tension.