It's been an interesting week. The computer I was using to run Mach3 and my
HobbyCNC driver board had a motherboard and power supply failure. Was able to
get a used HP COMPAQ DC7 in its place... Everything computer-wise seems to be
back in order.
HOWEVER I am running into Z-axis slippage(?) that I can't seem to troubleshoot:
My foam patterns take roughly 5-1/2 hours with both primary rough and secondary
finish cuts.
The primary always seems to run fine, but at variable places along the secondary
finish cut, the Z-axis looses its place and plunges the cutter twice as deep
into the pattern.
I did notice a 'stall' on the Z-axis when I did a fast move with Page UP and
Shift keys just now...
This may be indicating an intermittent problem with the motor itself?
I've already lowered my motor tuning lower than earlier working speeds.
In fact I recently had to replace my X-axis motor (425oz bipolar) for slippage
problems...
But I thought these motors were supposed to be pretty hardy...
More info...
I did a REF HOME for machine coordinates before starting the pattern.
I found my start point on the pattern and zero'd the X, Y, & Z coordinates, but
then went to the Machine Coord to see what that reading was: X .4133, Y .3504
and Z -0.6799
After the rough cut, the machine was supposed to relocate to the original X 0, Y
0 start point with the Z being at 1.5 for the tool change...
But when I brought the Z axis down to 0 to check the Machine Coord now read
-2.0334, instead of -0.6799
So is it motor slippage, or something else going on?

Not sure how to proceed...
So I decided to try just the finish cuts and eliminate the tool change.
But even that failed... each X-axis pass had the Z-axis plunging deeper...
(Yes, the Z-axis is rigid to the motor and table...)
Thanks for any insights...