Angle grinder - brush is sparking badly

I purchased a 9" angle grinder (Wolf) on eBay. After using it for about 30 minutes, one of the brushes started sparking badly. I could hear the arcimh amd and see the flashes right through the yellow casing! I removed the inspection cover and ran the grinder, I could see bright blue sparking travelling right around the commutator ()if that's the segmented copper drum that the brushes rub against) and flying out from where the nearest brush contacts the commutator. Is this something I should worry about, or is it normal? Is there any maintenance operation I can do to cure it?
Thank you.
Al
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PS.. I should have mentioned that the grinder is brand new - never used prior to purchase.
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AL_n wrote:

let brushes bed in, if it persists, take it back. Could be shorted turn.
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wrote:

An open coil is more likely than a shorted one. On an armature this small, single coils don't short, they go several at a time and so the fault for a short would be much more obvious than merely increased sparking.
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On Friday, 15 July 2011 14:40:30 UTC+1, AL_n wrote:

I was going to say that your machine is either a 110v fitted with a 240v plug or a 240V fitted with a 110v plug.
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Maybe we need to set up a home for old Angle grinders. Is there no Angle grinder museum yet? The number of queries, old and new we seem to see on this list does make one wonder if, in the future archaeologists will find these devices and wonder what early humans did with them, they will probably assume they were used in some ritualistic worship tradition or something.
Brian
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wrote:

Yes, I could send it back, but I was hoping I wouldnlt have to. But I guess I'll have to. It arcs really violently when actually cutting, i.e., when the motor is under load.
Thanks also to N.P.
Al
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AL_n wrote:

That is pretty consistent with a brush not being bedded in.
with electric RC/aircraft and brushed motors, its enough to make em unflyable - or was till the advent of 2.4Ghz sets.
The technique is generally to run for 10 minutes or more on no load. For the greatest mechanical wear and least arcing.
Once the brushes 'fit' the commutator it should stop. Apart from a sort of twinkling in the gap.

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Thanks. I tried that, but it was arcing as violently as it did under load, now. It sounds almost as bad a s Frankinstein's lab! I took the brush out to have a look, and it had worn down about 4mm-5mm! And there were bits chipped off from one edge. Is it worth trying to clean up the brass commutator a bit with a toothbrush or something? I guess it is abrading the brush for some reason. Perhaps some stone chippings got in there or something.. I was cutting concrete.
One thing surprised me: the wire that goes to the graphite brush is not fixed in! It goes into a hole in the graphite but there is nothing holding it in place other than good luck! Is that normal?
Al
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AL_n wrote:

No. It's a defective unit, take it back, and insist on a replacement or refund.
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Tciao for Now!

John.

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John Williamson wrote:

I am coming to the same conclusion.
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I have got the seller to agree to a large discount if I keep it, so I'd like to at least have a crack at repairing it.
I can see now that one of the copper contact bars on the commutator is standing slightly proud of the rest. I could have a go at flettening it down with some 1000 grade wet&dry.
I'm not sure why it would have become proud of the rest. Anyone seen that before?
Al
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Usual practice is to turn them in a lathe. You'll want more than 1000 grit if you try and sand it, and sanding is also bad as there's a risk of grit embedding in the copper, then turning into a brush-chewing device in the future. Mind you, modern brushes are a bit tougher than old.
I'd set up some sort of lathe centres to support the ends of the armature, then file it rather than sanding. An accurately circular commutator is important, else you get sparking across the dips.

Usually by a commutator segment becoming loose, which is a bitch of a problem to fix. Epoxy might do it, but it helps if you can get the segment out first - or else clean it and trust to thin cyano. On big commutators, they're sometimes drilled and screwed through the face (with a well-countersunk screw).
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wrote:

Thanks for the info.
I bought this Wolf gringer to replace my old CE one whose switch stopped working. The armature and brushes look almost identical, as if they may have been made by the same company. The new one is Wolf and the old one os CE. I'm just wondering if I can take the armature out of the old grinder and put it in the new one. Probably too much to hope for!
If I keep this faulty Wolf one, I get it for almost nothing. So I'd rather buy a new armature for it (or even get the old commutator professionally repaired, rather than pay out for a whole new grinder. I read somewhere that Wolf tools recently went bust so I don't know how feasable it is to buy components for them.
Al
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Hope the discount is large enough to cover the cost of a new armature etc - and that's assuming one is available as a spare. Isn't Wolf one of those once pround names now just made in China etc like everything else?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Friday, 15 July 2011 16:34:16 UTC+3, AL_n wrote:

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snipped-for-privacy@gmail.com wrote:

If it really is only one brush sparking it might be either sticking in the holder, worn too short or the spring is weak usually due to over heating. If they are both sparking then all probability is that the armature is knackered and usually new ones are more than the tool is worth.
At one time Wolf was a very good brand (1950s and 60s) but the name has been sold and appears on all sorts of Chinese low quality tools these days.
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On 10/16/2016 3:24 PM, Bob Minchin wrote:

2011 post so no point replying to that.
However *my* experience with various drills, vacuum cleaners, angle grinders, etc is that it is very often worth replacing worn out brushes. First symptom is sometimes device stopping without much preliminary sparking.
I agree that armature failure gives dramatic sparks.
If the manufacturer's brush prices are too silly, I've not had problems with eBay clones. Also, I've cut down or abraded larger brushes to fit motors on a number of occasions.
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On 16/10/2016 15:24, Bob Minchin wrote:

My Father has a Wolf muti set up ... Drill stand,wood working lathe, circular saw, jigsaw ... all powered by wolf 2/8" single speed hand drill. All in cast aluminium not a piece of plastic in sight. The set is now more than 60 years old.
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