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?
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
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.
This newsgroup posting comes to you directly from...
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.
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?
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
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
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).
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.
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?
*Save a tree, eat a beaver*
Dave Plowman email@example.com London SW
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
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.
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
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.
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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