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Little OT- Angle Grinder question

Hi there... I am a pipeline welder of 25 years and I had a "stack" of non working Makita angle grinders (mod 9005b) under a bench in my shop, that had let me down over the years. Last night I decided to take these things apart (with a bottle of J&B) and try and salvage a few of them by swapping parts etc. I managed to make three good ones by swaping parts. I have three other grinders that would be good ones if the brushes would quit arcing against the armature. When I took the brushes out, they were burnt on one side so I went into the city and bought new brushes. I installed them and get the same result. I took the armature out and put some emery cloth on the bearing surfaces where the armature meets the brushes, but get the same blue sparks comming out of the grinders. Is it the windings that are shot? Am I beat here? is there anything I can do? or are they off to "Grinder heaven"? Thanks for any words of wisdom on this subject....Regards...Jim

Reply to
Jim & Lil
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You have to get the armature commutator smooth and true. If you use the wrong abrasive it will leave conductive bits in the copper. I set the armature up in a old bearing in a flange. I then drive it with an electric drill chucked to the free end of the shaft. My helper would spin the armature while I dressed the commutator with a lathe file which is single cut with a steep angle. Technically you are supposed to undercut the mica strips between the copper bars. I didn't bother. You might have a bad armature. You can dress the commutator as I describe or if you have access to a lathe even better. In a small motor you cannot take much off. I would try a proper dressing of the armature and then if no success it is time to discard for parts. Randy

"Jim & Lil" wrote in message news: snipped-for-privacy@corp.supernews.com...

Reply to
Randy Zimmerman

Reply to
Roy J

Thanks all for the replies...I am off to the shop to try a few of your ideas...warmest regards...Jim

Reply to
Jim & Lil

If you can't find a rebuilder of small AC motors, then try a _car_electrician, one that has a machine shop and rebuilds alternators and starters. There's not that much difference between a brushed motor in an angle grinder or in a starter motor.

You true a communtator on a lathe, and you may use abrasives to clean or polish it. Don't use emery - it can embed in the soft copper.

Undercutting the commutator insulation isn't usually needed, as these are moulded in a resin rather than assembled from paxolin or mica.

If you do have a shorted winding, then a machine called a "growler" will detect this.

All of these skills are rare in this disposable age, but they're all well-established car mechanic skills. If you find a 1950's textbook on such, it'll describe how to do them

-- Socialism: Eric, not Tony

Reply to
Andy Dingley

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