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View Full Version : Die Grinder - motor question, service?



Arthur.Marks
08-05-2011, 03:29 PM
This is a speculative question. I've learned a lot about electricity, wiring, etc in the last few years, but I am still a beginner regarding motor construction. I have a Milwaukee brand electric die grinder I bought 'refurbished' from CPO years back. Last year I was pushing it really hard on a job, and it started smoking. I left it alone for a day, and it runs. It has felt "gritty" and sounds different ever since. So do you think...

I partially burnt some windings?
The bearings just need replacing?
Is it still safe to use?
I have a multimeter, what could it tell me?

I've been meaning to take it to a service center, but the closest is a good hour's drive. I would be worried of just mailing it; I would like to talk with the tech first to see if I am just worrying too much, or it isn't worth fixing. I know it is more of an idealogical hang-up, but a direct replacement isn't very appealing. Mine is one of those made in the US before Milwaukee moved the production of this model to China.

millwrong
08-05-2011, 05:28 PM
Seems to me my Makita is a brushed universal motor. You sure you don't have the same/similar? Usually the "gritty" feel is brush related. As to the windings, you definitely cooked the varnish,however it still runs, so unless time and jobs demand it, run it!

Rustybolt
08-05-2011, 05:56 PM
The brushes ride in little plastic pockets molded into the housing. Once these are melted the tool is trash.
So far, at work, the hands have managed to melt, a Milwaukee circular saw, a 41/2 inch angle grinder,Milwaukee and a 1/2 inch Milwaukee Hole shooter.

Arthur.Marks
08-05-2011, 06:48 PM
The brushes ride in little plastic pockets molded into the housing. Once these are melted the tool is trash.
Once I read that, I decided to do some exploratory surgery since there is no warranty left anyway...
http://s771.photobucket.com/albums/xx357/Arrak_Thumrs/Widgets/Milwaukee%20Grinder/
I am very surprised. Given how different it feels, there is no obvious damage at all. Maybe I just unbalanced it with whatever magic smoke came out? It does run at 21,000rpm after all. It wouldn't take much of an imbalance to feel really off. Following on this line of reasoning, maybe the noise is from the gear mesh being affected...

I don't know.

Arthur.Marks
08-05-2011, 06:49 PM
BTW, I'm assuming this is a "brush"?
http://s771.photobucket.com/albums/xx357/Arrak_Thumrs/Widgets/Milwaukee%20Grinder/?action=view&current=DSCN4978.jpg

[EDIT] That's weird. It feels like it did before "the accident" after reassembly. Maybe those brushes had shifted? Still "I don't know", but better than the last time I wrote that!! :)

topct
08-05-2011, 07:05 PM
I would check "all" of the bearings. Then I would have to check the armature. One bad segment will let the thing run but......

Brush looks good. Bad bearing or armature.

Arthur.Marks
08-05-2011, 07:07 PM
Brush looks good. Bad bearing or armature.
Bearings felt good. Is this an armature?
http://s771.photobucket.com/albums/xx357/Arrak_Thumrs/Widgets/Milwaukee%20Grinder/?action=view&current=DSCN4973.jpg

topct
08-05-2011, 07:23 PM
Bearings felt good. Is this an armature?
http://s771.photobucket.com/albums/xx357/Arrak_Thumrs/Widgets/Milwaukee%20Grinder/?action=view&current=DSCN4973.jpg

Yes. Doesn't look to have gotten hot. Are all of the segments, the part of the armature that makes contact with brushes the same color? When you look at those segments is there a clear space between them? They are not smeared and possibly making contact with an adjacent segment?

Without the armature in place are the brushes free to move in their holders. They are not hanging up?

Milwaukee makes quality tools. They are worth exploring$ their fixing.

Arthur.Marks
08-05-2011, 07:49 PM
Without the armature in place are the brushes free to move in their holders. They are not hanging up?
You likely missed my update above, but after I put it back together from taking the pictures it feels normal again. I'm beginning to believe it had something to do with the brushes. Specifically, this one:
http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/Widgets/Milwaukee%20Grinder/DSCN4977.jpg
The whole connector with the brush seats less securely than the other one. This is the other one:
http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/Widgets/Milwaukee%20Grinder/DSCN4978.jpg
I'm thinking it was somehow knocked out of position. Without the armature in place or the top, it very much wants to skew to a sharp angle due to the wire running behind it. Maybe it lost contact or something. So far this has been the easiest fix ever :p Take it apart. Put it back together. That's almost equivalent to "just hit it, why don't you!" :D

topct
08-05-2011, 08:10 PM
The devils in the details ain't it. Such a little thing.

Good job.

Dr Stan
08-05-2011, 08:12 PM
So far, at work, the hands have managed to melt, a Milwaukee circular saw, a 41/2 inch angle grinder,Milwaukee and a 1/2 inch Milwaukee Hole shooter.

Wow! Guess you need to buy stock in Milwaukee. :D

Arthur, glad to hear you had such a simple repair. As has been said, Milwaukee (at least they did) makes good tools. I too have several US made versions of their power tools and am quite happy with them.

For me its either Milwaukee or Bosch.