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why did my angle grinder stop working


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I was cutting some steel and stopped for a second to adjust the extension cord, then when I tried to start again, the grinder had stopped working. I tried other things on that extension cord, and it worked fine. I checked some wires in the grinder, and nothing seemed out of place. please help

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It over heated. Cut off disks require a LOT more power than grinding or sanding so unless you have a light touch the motor gets hot. When an electric motor reaches a set temperature it shuts off until it's cooled below the limit.

Frosty The Lucky.

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I would tend to think bad connection in the cord, switch, or less likely, the brushes getting a crap connection. Frosty may well be right, but I don't think any of mine have a cutoff for overheating, so I'm not experienced with it. The cord you can jiggle (carefully) to see if it cuts out, or test for resistance. Switch you pull out and test for resistance. Brushes you take out and look at them and while you're at it, make sure the commutator is clean and not scored. And if you've got them out, why not replace them. You can clean a commutator by sanding with a VERY fine grade of sandpaper, lightly, then cleaning out the grooves with a probe or thin screwdriver.

I just had an old favorite, a Bostitch start making popping noises once in awhile, acting weak, and getting hot while using the cutting disc, so I'm guessing I've fried the brushes and it's arcing to the commutator (the bit of the armature that the brushes touch). Or maybe some of the carbon has got down in there and is arcing. I'd fix it, even if it costs more than new. I've had that thing for around a decade and love it.

You kinda get attached to them. I've got three, one Bostitch, one Dewalt, and an $11 HF Chicago Elecric special that just will not die no matter what I throw at it. I've bought three of the latter over the years, almost more out of morbid curiosity than anything. One lasted about 30 minutes before the windings started smoking, one lasted maybe six months before the brushes went and I gave it away, and the other has been going for maybe eight years now, zero maintenance. It's the Nash Rambler of angle grinders, clunky, awkward, and people look at you funny when you use it, but it just will not die.

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I've had a couple of the cheaper angle grinders start cutting out at the switch. There the type that have a plastic switch that slide to a locking position. Sometimes on sale at Harbor Freight for $9.95. I've had the best experience with the 15 amp paddle switch 4 1/2 inch grinders from Dewalt.

I'm not talking about the name brand angle grinders when it comes to the slide type switch. 

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Took mine apart enough to pull the brushes this morning. No bueno. One was reasonably okay, maybe worn down between a third and a half. The other was around a quarter inch shorter, the wear was slanted, and there was a chip missing out of the shorter side. Gotta take it apart some more to get a look at the commutator. That thing is buried in there more than I thought. Turns out nobody local carries bloody carbon brushes either, so I'm ordering a variety pack and making Jeff Bezos a little richer.

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Took the rest apart, worse than I thought. The windings are burned on the armature, just below the commutator. I'm not good enough to rewind one, and I've been losing my mind for two hours trying to hunt down a replacement. Seems like they sell one for every brand but the Bostitch BTE820. Anyone know if they call it something weird, or just don't carry them anymore? Well used or not, I don't want to throw out a $100 grinder over a $30 part.

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The ones I found for Dewalt grinders look a bit fatter and shorter. The ones for Makita actually look pretty close, but I'm hesitant to mix and match. Called the service center, and got a wonderfully helpful foreign national, Alejandro, who tried very hard, but didn't have much more to go on that what was on their website and I'm not sure knew an armature from a backhoe.

Is there nothing Gingery didn't do at some point? Yeesh. I'm surprised he hasn't wrote a book on do-it-at-home gene splicing.

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Well, found a close match...in a Makita 9556. All the dimensions work except the screw end going to the gear box, which is 6mm to the Bostitch's 8. But the 9556 is designed for 220V, so if I recall correctly, that would draw a bunch of extra current and burn up the windings. No bueno.

And while I'm at it, picked up a caliper to measure all this mess, and it was reading exactly half what it should. Ended up having to pull the batteries and short the terminals to reset it before it worked right. Maybe rewinding is the way to go. It looks simple enough, but knowing how a motor works in theory and rebuilding it are two very different things. Screw up an intake gasket on a 318 and make a hidden vacuum leak say, and your Carter carburetor will never forgive you. I can't imagine it's better with electric motor.

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It seems like running the armature of a universal motor below rated voltage should have the same effect as running a permanent magnet motor at reduced voltage—the motor happily runs at reduced speed. But even if I’m right, that’s probably not what you want. 

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9 hours ago, Nobody Special said:

Well, found a close match...in a Makita 9556. All the dimensions work except the screw end going to the gear box, which is 6mm to the Bostitch's 8. But the 9556 is designed for 220V, so if I recall correctly, that would draw a bunch of extra current and burn up the windings. No bueno.

And while I'm at it, picked up a caliper to measure all this mess, and it was reading exactly half what it should. Ended up having to pull the batteries and short the terminals to reset it before it worked right. Maybe rewinding is the way to go. It looks simple enough, but knowing how a motor works in theory and rebuilding it are two very different things. Screw up an intake gasket on a 318 and make a hidden vacuum leak say, and your Carter carburetor will never forgive you. I can't imagine it's better with electric motor.

Install it and upgrade the shop to 220V.

 

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About now I'd be looking at new angle grinders. You've spent an awful lot of time on this, I could spend a lot less mowing lawns, picking up dog poop, etc. and earn enough to buy new. There's a point where things are just not worth the effort and expense.

Frosty The Lucky.

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