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
If the armature and field pass the eyeball test (i.e. no broken wires or
obvious burnt spots) then there are a coupla other things you can try.
1. have the commutator (the part of the armature that the brushes contact)
trued up on a lathe. They sometimes get a little egg shaped after much use
and will cause arcing. A full service tool repair shop will be able to do
this for much less than a new armature, but call around cause they will most
likely want to just sell you a new one. I can't recommend rewinding because
it causes over-amping.
2. apply some spray on insulating varnish to the field and armature. apply
only to the coils/ windings, mask everything else.
You could just take them to your friendly neighborhood tool mechanic. let
him test your armatures and fields... bring beer : )
and I wouldn't trust anybody that had "sales" as part of their e-mail
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