Z axis waviness artifact in contour milling

Anyone doing fine contour milling with their Haas? We have a 2008 OM-2A that consistently produces a wavy surface where it should be flat or smoothly undulating. It appears that every ~0.85mm of Z travel, the Z axis is low by a few micron, so that no matter how we mill a part, we see horizontal stripes in the play of light on the surface. I put a micron gauge in the machine and found that the Z axis can take a while (seconds) to settle at certain heights -- again, roughly 0.85mm apart. I suspect this is a control issue and not a mechanical one, because there's no simple relationship to the Z screw pitch. I wonder if the problem is unique to our machine, or if others have seen the same motion/positioning artifact and found a workaround.

I know the "settling" you mentioned. You can often hear it on the larger machines, and you can watch the position correction move around when in diagnostic mode.
But I can't say I've had much issue with it when actually engaged in a cut. I have more trouble trying to get rid of the polygonal smoothing leftover by the CAM software's filter.

I should mention that I've never used an office mill, though...

Microns,

What are your Z backlash (parameter 41) and Z friction comp (parameter 140) parameters set to? I would run a ballbar test, make sure if you do that the tech runs the Z axis! Most take the easy route and just run an XY test.

Thank you,

Phil

As PMT mentioned, you should check for backlash in your Z axis ballscrew. Also check for tool deflection. What spindle RPM are you running?