[rabishop]

We have a Haas VF6 that drops .025" in the Z axis during cutting without a change in the Z position shown on the control. Once the Z axis drops that
.025" it doesn't change any more.

[ToyMaker94566]

If you're certain you're not sucking a cutter, it sounds like your Z axis motor is failing. I had a similar problem a few years ago with my VF3. The service tech put a new motor in and that was that.

Oh and a $1200 bill later...

[cncserveng]

Check the belt if it has one, for tension and condition. Check there is any wear in the pulley or coupling.

Is the axis brake sticking on ? it could be holding the axis until it releases (check the brake relay is good).

Check the feedback unit (encoder) on the motor or end of ballscrew connections are tight. Make sure the motor and the ballscrew nut screws are tight. Check the counterbalance weight (or Cylinder) system is ok (free and working).

Finally, measure the axis for backlash. In handwheel, in 0.001" pulses, how many clicks do you need in either direction till it moves ?.

If the mechanical checks are all ok, the problem then has to be electronic, possible fault with axis encoder or axis board.