View Full Version : Motor vibration

03-06-2011, 04:24 PM
I've mounted a DC motor (http://www.electricmotorwholesale.com/index.cfm?fuseaction=catalog.prodInfo&productID=3267&categoryID=249) on my lathe and have had great success with it up until about a week ago.
(I didn't pay anywhere near that price either!)

Felt a vibration in the lathe and traced it back to about .001' run out of the motor shaft but which can't be felt by hand with the motor off trying to move the shaft back/forth/sideways, etc.

Could that still be a bad bearing without any noticeable feel of it in the shaft or what might it be?

The motor has not suffered physical damage.

J. R. Williams
03-06-2011, 04:35 PM
Run the motor without the pulley installed and check the vibration level then install the pulley and run the motor. I would expect you have more run-out than what you stated with the pulley installed.

03-06-2011, 04:49 PM
As far as the motor itself, I can't imagine that it would suddenly go from no runout to some runout, unless the bearing is loose on the shaft and has shifted to one side. Chances are the runout was there from the start, and the pulley has shifted somewhat. Maybe you'll find that you have enough room between the pulley and the shaft to shim it for truer running.

I had a 'funny' a few months ago. My table saw suddenly started having a bit of vibration, then after a short time it got worse. I couldn't see any reason for it, but then I took the belt off and pulled the motor pulley. It was cracked on one side. That pulley had been on there for 20 plus years, so it was probably tired. I replaced it with a cast iron pulley- not only was that a better fit to the shaft, the belt runs truer as well.

There is the possibility inside your motor that some windings have come loose and stretched a bit to one side. That would throw the balance off. But as JR said, run the motor with no pulley on it and see how it behaves. If the motor itself has developed this vibration, it's going to be more difficult to deal with.

03-06-2011, 05:41 PM
That IS with no pulley.

DTI right on the shaft next to the front bearing.