Growling noise on spindle decel?

I'm looking for some guidance on a new-to-me machine. It is a vertical machining center, Milltronics Partner 7 with 12.5hp CSM spindle motor and MPA-50 drive. The spindle needs bearings which is no problem, I'll be sending that out shortly for rebuild. The issue I'm wondering about is a growling noise when the spindle decelerates, for example from 2000 to 500 RPM.

The best way I can describe the noise is what you hear with a cheap bench grinder when it hits its resonance during spin-up or spin-down, not a nice sound. While the noise itself isn't an issue I am worried that the noise is indicative of a problem that needs to be addressed.

I disconnected the spindle belt and the noise remains, so it's an issue with the drive or spindle motor. If it makes any difference I am running the machine on single phase, 232v after the buck converter that I wired up.

Any ideas?

Frank.H said:

..........I disconnected the spindle belt and the noise remains, so it's an issue with the drive or spindle motor.....Any ideas?

Click to expand...

sure easy way to see if it is the drive or the motor: COAST DOWN TEST!

Just run spindle up to max speed, then disconnect power to the drive - SO THE MOTOR IS SIMPLY COASTING DOWN WITH NO DRIVE ACTION. If the noise remains, it is in the motor: if the noise is gone, it was in the drive.

EASY HUH