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
Reply to
Jim & Lil
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Look at the area that the brushes contact. If there are one or two contacts that appear to be eroded or burnt, while the rest are not, the winding is probably shot. The motor usually will still turn, but the brushes will spark something fierce when it runs. Toast!
Cheers Trevor Jones
Reply to
Trevor Jones
The symptoms you describe tend to indicitive of a shorted armature (rotor) winding.
Reply to
MP Toolman
Open armature windings will cause heavy sparking and can sometimes be resoldered where they connect to the commutator bars.
Don Young
Reply to
Don Young
First of all, you'll never get rid of ALL the arcing. If you've got big flames shooting out, that's a problem. If there's only a little arcing, put 'em back together and put them to use.
Arcing can be caused by many reasons, the first that I would expect is low spring tension. You put new brushes in, so that shouldn't be the problem.
You used emery cloth on the commutator, which isn't cool. The sticky junk on the emery cloth will hold the abrasive on the com or brushes, and cause excessive wear. Regular garnet sandpaper would be a better, readily available choice. It's of no matter now, just make sure you clean everything off well before putting back in service.
Do whatever you can to make the commutator nice and shiny smooth. A fine file might be of use. Improvise if you have to.
IMPORTANT: Check the insulation between the commutator bars. It should be LOWER than the bars themselves. It's possible that the insulation is as high as or higher than the bars, which will definitely cause arcing. Make a scraper tool to hog out the insulation a little lower.
As others have suggested, you might have bad windings. Take your ohm meter and measure from one commutator bar to the one directly opposite. Do this on every pair of bars and you'll want to see readings that are close. Do the same for bars that are NOT opposite one another. You'll want to see resistance in the megohm range. Try measuring each bar to ground (armature shaft), again looking for high resistance or open.
=-=-=-=-=-=-=-=-= Rob Skinner La Habra, California
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Reply to
Rob Skinner
The 9005B had a problem with commutator segments lifting out of the insulation. If you have some that have lifted just a bit, they're hard to see and may be making the brushes jump around and arc. Turning them in a lathe is the only way to true them up, but the fact that they've already started coming out makes it almost pointless. If they're OK, it's bad armature windings. That little grinder works hard and it's a wonder it lasts as long as it does. I have one here that needs a field winding assembly; I have a brand-new armature for it.
Reply to
Dan Thomas
Thank you all to replied...have just turned the heat back on in the shop to try a few ideas you all have told me. i printed out your suggestions Rob Skinner. I think if I get good steady readings with my ohm meter, I am going to put the armature on the steel lathe and lay some sand paper to the commutator to make it nice and smooth ....
Reply to
Jim & Lil
Don't use paper to skim the commutator.. Most people i know use a proper tool and skim the segments. paper will simply conform to the differing heights of the segments and knock the corners off instead of returning the commutator to a true cylinder.
If this observation is incorrect I'm sure someone will speak up.
Reply to
Des Bromilow
Grinder Armature. The correct method to check the armature is to use a tool for checking the armature for shorts - a Growler. The resistance between bars in the armature is very low.
J.R. W
Reply to
J.R. Williams
Nope, you're quite correct. Had a VW generator once that sparked like hell, did the recommended bit with the abrasives, had a nice shiny commutator afterwards. Still sparked badly, so bit the bullet, hauled it off the car and took the armature down to the lathe. In the armature chucks, that commutator was .030" out of round. A couple quick passes with a polished commutator tool and it was concentric once again. Did the undercutting with a ground hacksaw blade and it was good for another 100K miles. Changed out the brushes, too, as long as I had it down that far. So just polishing things up doesn't always do it by itself. My dad got a set of armature chucks in with some mixed tooling a long time back, they've paid for themselves over the years with small motor and generator repairs like that one.
Reply to
Stan Schaefer
When I bought my used Atlas 10" lathe it came with a set of armature chucks from Jacobs. Can anybody show me what the armature tool for doing the turning looks like? Just in case I need to use the chucks on day.
Reply to
Doug Arthurs
check out:
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Doug Arthurs wrote:
Reply to
Rex the Wrench

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