Cause for Angle Grinder Burn Out

MFan

Member
I had a 4-1/2 inch Milwaukee angle grinder that had the motor start growling and smoking when I was using it. I had been using it for a while and the motor case was warm, but I made the mistake of thinking a Milwaukee would hold up in some extended grinding.

I"ve replaced the grinder with something that has a better replacement warranty, but I"m wondering what went wrong in the motor?
 
One of the problem with any grinder or chop saw etc that is used to work with metal is the small metal pieces that you grind off often times gets in and around the brushes and bearings and bushings which in turn cause them to burn them self's out. I pull the brushes out of many of those things from time to time and blow them out so as to get longer life form them
 
ONE thing that helps keep temps down is to use as short of an extension cord as possible and a good-sized one.
 
Usually when they growl it's from losing a section of winding or the commutator. Often seems to happen more random than necessarily overheating but hard to say. I have seen many damaged from small bits of slag running thru them. It happens
 
An issue I've seen is people holding them in both hands, and putting one over the gearbox. In many cases, this blocks the air flow through the motor, causing it to overheat.

The reason I know this is I had it happen to one quite a few years ago. I didn't even realize what I was doing as the gloves I usually wore kept me from feeling the heat I was blocking in.
 
When the guys at the mine used them they would work the snot out of them, push them to hard, never lasted all that long!
 
The quality of Milwaukee grinders ain't what it used to be. Now made in China.

Last one, THE last one... Gave it up in record time, never sounded right from new. Replaced it with a Makita, so far so good!
 
Hello MFan,

Sounds like brushes to me. Poor contact to the commutator will make the motor growl, hot, throw sparks and run hot. That's my guess

Guido.
 
I agree with Bob. Use a heavy cord and try to avoid short runs and stops. I have seen some people press the switch several times like a gas powered weed eater or chainsaw. This can damage the motor or switch
 
Also, at least once a year, repack the gear-head with fresh Grease. When those grinders come from the factory, they have barely enough grease in them to provide minimal lubrication; and the whirling gears sling that grease everywhere except where it's needed ... on the gears.
 
I think there are several different levels of Milwaukee 4 1/2" grinders, graded by amp draw. I have seen amp listings from maybe around 8 to 12 or 13. The higher amp ones cost more, but with a heavy cord should be heavier duty than the lower amp ones.
 
Mfan,
When the rotor rubs the stator, it will cause growling and go up in smoke. Take it apart, the end that rubbed the stator will have scratches on it. That's the end that has a bad bearing or bushing.

Sometimes, there are carbon deposits between the commutator segments that will cause flash over and smoke the rotor. Look for burnt insulation, it will be black. But that usually doesn't cause it to growl.

Look to see if the brushes were too short or it chipped a segment on commutator.

Almost all tool sold have different grades of quality. My rule of thumb when buying a right angle grinder is look for one that uses the most amps. More amps means more hp.

I never push my tools when grinding or cutting. Let them make sparks and take my time. I have two grades of right angles. An old B&D, it uses 6 amps and is down on power compared to a dewalt that uses 10 amps. I don't use mine steady and get them hot, I give them a rest.
 
Several years ago there was a LARGE discussion on 4-1/2" grinders here. It should be in the archives if you have time to hunt it. Seems like Bosch and Makita were the overall favorites.
 
Go to harbor freight and get a couple of theirs. Keep one on the shelf and when you burn it up toss it in the trash and get the spare. Two HF grinders will be less than half the price of a Milwaukee and probably last just as long. I've been using them for years and have only burnt one.
 

I buy Chinese (Harbor) Freight Chicago Electric angle grinders 4 at a time because I abuse them by using cut off wheels on steel all the time. Do not get the cheaper Drillmaster ones - they are truly junk. You want the Chicago Electric ones. They will last as long as a Milwaukee but don't cost much of anything.
 
What NC WAyne said about blocking the air flow with your hand is very true and you have to watch for that. Also the byproduct of the grinding , grinding dust is killing the motor and worse in a Corvette or fiberglass shop the glass dust.
 
Just to add, make sure to match your grinder to your work. 4" and 4 1/2" grinders are great for light grinding but for more cutting and pressure they wont hold up. A 7" or 9" would be better to use. My dad had a Makita 4" and a Skil 4 1/2". The Skil had a lot more power.
 
I like most of the Milwaukee tools I have. The last light duty 1/2 inch hammer drill I bought is a POS. I think it's the way of the market today build cheaper and keep prices down. There are not enough people that will buy true professional grade tools.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top