C Axis vibrating on lathe

I recently looked at a used lathe that I'm considering purchasing. It's a Mori DL with opposed spindles. The C axis for the right spindle has a weird vibration to it. The left side spindle is fine. It's most noticeable when jogging the axis at a low rpm. It feels jerky, but at a high frequency that has me sure that the problem is electronic. As I jog it, the vibration varies in intensity. Once I stop jogging, the vibration usually diminishes for a few seconds until it goes away. Once I was able to stop at a position where it didn't go away. It just sat there humming away. In spindle turning mode, it is quiet and feels smooth.

I'm looking for any ideas on what this could be. Bad drive? Motor issues? Parameters need changing? Could it be just that the gain needs to be adjusted? I believe the motor is integral to the spindle and that there is no separate C axis drive motor that engages when going into milling mode.

Thanks in advance for your responses.

The C-axis feels "jerky"? That's not good, it'll make it very difficult to Mill parts.

It vibrates when you jog it too? Does it vibrate when you give it a programmed feedrate?

I've seen this before under different circumstances. IE, when C is engaged without the brake. Mori made it tricky on few of the Machines. A sequence of events needed to occur, especially when using a Sub. Engage C, engage B, sync A and B, disengage B, engage C brake, disengage C, engage B brake, etc, etc.

R

I find out if it's belted or not, but I had an issue with a lathe that milling in transmit mode live tools on the sub, it jerked around and turned out to be a loose belt.

Yes, the C-axis feels jerky. I would guess that the vibration would show up on the part when interpolating.

I didn't program a feed rate. I just used the jog (not rapid) button and played with the override to get different feed rates. I think that would be the same as having a programmed feed rate.

I'm 95% sure there is no belt. I looked under the cover when I was there and only saw the spindle. I have an older version of this machine, and it also has a direct drive, integral spindle motor.

On my older machine, there is a disc brake that clamps with very light pressure when the C-axis is engaged. If that isn't coming on, I wonder if the axis would vibrate like this? I kind of doubt it, as the vibration seemed quite abnormal.

Does any body else have any ideas on this vibrating C axis issue? My boss wants to move on this machine, but I'm worried that it could be a can of worms. I'm assuming the drive needs work, but if that's not it, then I'm at a loss for what to do.

Call a professional...

You're literally asking us to guess. Then you might move forward on one of our guesses, that will piss the boss off, if it doesn't fix it.

R