Noisy Axis problem.

[xray_man]

Hi guys,
A few years ago I converted a New Hermes engraver to CNC using Xylotex drives and Mach-3 controller (my post describing details is on this forum).  Well, I recently noticed a "growling" vibration coming from the X/Y table when I move it in the +Y direction at high speed. All other axes and directions are smooth and quiet. My Y axis carries the X axis motor and lead screw, therefore it carries the biggest load (if that makes any difference). When I jog the Y in the positive direction, the table starts out smooth and quiet but then starts to growl and vibrate after a second or two of movement, becoming louder and stronger over a short distance. It seems to me like something is mechanically resonating, but I'm not certain. I tried retuning the Y axis using different velocity and acceleration numbers, but that did not help unless the table moves very slowly (which is unacceptable).  So, my questions is, Is there some way to filter the resonance/vibration in the Mach-3 software? All axes use standard stepper motors.

Thanks!

[Tweakie.CNC]

Just from memory because it is a long while since I looked at the Xylotex instructions but if it has a PFD (percent fast decay) pot (adjacent to the current adjust pot) associated with each axis you could try a slight adjustment of this on the axis that is causing trouble.

Tweakie.

[Hood]

Have you checked the mechanical side of things? Loose bearings, tight ballscrew, loose mounts etc could allow for things to start to vibrate.
Hood

[xray_man]

Just from memory because it is a long while since I looked at the Xylotex instructions but if it has a PFD (percent fast decay) pot (adjacent to the current adjust pot) associated with each axis you could try a slight adjustment of this on the axis that is causing trouble.

Tweakie.

Hi Tweakie,
There is only one pot adjustment for each axis on the Xylotex board that I have, and this adjustment is called "Vref" which affects the maximum current that the drive will supply to the motors. Those pots should have no effect on the vibration that's occuring.

Thanks.

[xray_man]

Have you checked the mechanical side of things? Loose bearings, tight ballscrew, loose mounts etc could allow for things to start to vibrate.
Hood

Hi Hood,
Yes, that was the first thing that I looked into. I made sure that there wasn't any backlash in the lead screw, and that it was properly lubricated, etc.  The -Y axis movement is smooth as silk! It's only in the +Y direction that the noise occurs.

Thanks.

[Hood]

Have you tried the motor disconnected from the axis? Also might be worth a try swapping motors.
Hood

[xray_man]

Have you tried the motor disconnected from the axis? Also might be worth a try swapping motors.
Hood

I don't understand how disconnecting the motor can prove anything because the vibration doesn't occur unless the axis is moving fast enough. I certainly can't spin the ball screw fast enough with my fingers!  As far as swapping motors, I'll only do that after trying every other possibility because that would be a major job.

[Hood]

I was wondering if the vibration is in the motor or the way its being driven rather than in the axis.
Hood

[xray_man]

I was wondering if the vibration is in the motor or the way its being driven rather than in the axis.
Hood

Good point!  I'll play with that and see what I can come up with.  I was hoping that Mach-3 had some sort of filter parameter that I can adjust (like some industrial CNC controllers have).

[xray_man]

UPDATE:  I was wrong.  I didn't think that the drive current would make a difference, but when I adjusted the Vref pot for the Y axis, which now provides a little more drive current to the motor, it cleared up the noise!  Apparently, my Y axis was struggling to move the table at high speed, and so the drive became unstable. Now I can jog the Y axis in either direction and it moves without growling at me! 

YIPPIE!