electric motor noise

I bought a Miller Dialarc new back in 1980. The machine had about 1/2 hour running time on the machine when the cooling fan motor started to make a noise. I took the sheet metal off the welder and wanted no part of fixing the motor. Now 35 years later it was not a bad job. I took the motor out and apart and went to a bearing house and asked for bearings for the motor and the guy there told me that the original bearings were good and did not need replacing. So I put the motor back together and into the welder. I noticed taking it apart that the hub the fan blades are on, on the armature had the Allen screws finger tight. Putting it back together I tighten them good and thought that was the noise problem.

There is still a noise, anyone have any ideas.
When that machine was first turned on that fan was as quiet as a small man fan.

Is the fan blade out of balance? dirt on it or maybe lost a spring clip weight from the blade.

JOB,
Were there scratches on the rotating part of the motor, rotor? A bad bushing or bearing will allow the rotor to rub the stator and leave scratches, usually on one end.

Does the rotor spin freely? Is the rotor centered properly in the fields windings?

Is the amp draw is normal, is motor over heating, Fan blade is good? If everything checks out good, I would ignore the sound, turn up the shop radio. geo

Are the bearings sealed? If not can you get lube on them? Ron Mn

bearings are sealed, they felt good, turned nicely. Even the guy at the bearing house said there is nothing wrong with the bearings.

When I had the motor apart I did not notice any scratches on the rotor. The motor turns over real smooth. Having the motor apart I don't see how the armature could have moved out of center with the fields.
Not sure on the amp draw. When the motor started to make noise I stopped using it and it had sat on the shipping skids ever since. I now have it on a stand and just wired it up yesterday. The fan blade should be good, it has only spun for about 1/2 hour since new.

I will take the sheet metal back off the welder and maybe feel the motor when running, if I can get my hand in there without touching anything else.
I don't like the sound so I might ignore it for awhile. I would like to fix it though.

The rotor should be close to magnetically center. How big of motor are you talking about? Can you post a pic?

The welder has not ran long enough to get dirt on the fan blades so that should not be the problem. When I first took the sheet metal off the welder I did not think about any spring clip balancing weight. I did not notice any marks on any blade where one could have fell off. I will look today. When the welder was running it ran quiet. then all of a sudden it started to make this noise. It did not gradually get up to this noise level.

This welder has sat on a wheel under it's cardboard shipping carton for most of it's 36 years. I have a little Tig job for it now or it might still be on that wheel.
Here is what the welder looks like today.

I will take the sheet metal off the welder today and post a picture of the motor, it,s not real big, maybe 6 inches in diameter.

Nice hearing from you Ron, should stop in and see you. Wife has got worse now and I can't leave the house without taking her with.

Check where the fan blade and the hub are crimped together. I have seen the aluminum blade slip inside the steel hub that mounts to the motor shaft. Usually this only happens on start up but its worth checking. What I have done is take a chisel and cut a slight dent in the curled crimp. The resulting dimple locks the hub to the blade.

I guess I would just replace those bearings or pop off the seal and oil them. Ron Mn

try it without the fan on it, a fan can be balanced using a lawn mower blade balance (sometimes)

If the fan is crimped into the fan hub, and the crimp is not tight enough, they will make noise.

After all you guys suggestions I figured I better take another and better look at that motor. As you can see in the picture the motor is not real accessible. All the sheet metal comes off except the front panel. It took me about 45 minutes to get the motor out. Before taking the motor out I discovered there was some vertical play in the armature shaft. The fan blade had to come off before the motor could be disconnected and removed. The motor plugged in on the bench ran sort of quiet with a little noise. Blade on in the welder there is too much noise.

Taking the motor apart and miking the outside diameter of the bearing and using a telescoping gauge and mike on the front bearing motor hub I found there was .006 difference. So when that motor casting was machined someone somehow took out too much metal.

I feel when that motor was assembled something was put between the bearing and hub to take up the difference. And that fell out after a little bit of run time and the noise started.

I doubt I can buy that motor part. Shimming was suggested by a friend. So not sure what I am going to do now. I expected better quality from Miller.
When I bought the welder I did not have the means to lift the welder except with a chain hoist. And the one year warranty expired when the welder sat on the pallet. At that time Miller said I was out of luck when the noise started.

Thanks for you guys suggestions.

Turned out not to be the fan.

That fan is a little out of balance, there was a little bit of a heavy spot. A little bit off over machining was the problem.

A replacement motor from Miller is $170.00. It is not the same one that was in it originally. I decided to try the shim around the bearing.
We cut a piece of .003 brass shim stock and put it in the motor casting and lubed the shim stock a little and taped the bearing into the hole, all except maybe 1/16 of an inch. Then put the rest of the motor together and used the four bolts to pull the motor together tight.

The motor is back in the welder now and sounds real good. No more noise except air movement.

Harmonics and electrical noise will make some motors rumble. Could "uneven" power be causing the noise ?

So far so good looks like the shim stock fixed the problem.