No, no error messages.
But I did make another observation... The Z-axis is stable during the duration of a cut, it only drifts when it is on it's way to the next cut. It's almost like it's easing in....

try a 0.1uf cap from each input to ground, has worked for me in the past.

Angel Tech, thank you!
BUT they're already in place!
Remember I'm only getting the drift when the Z-axis is on it's way to the next location.
No drift with shuttle, or at specified depth...
Seems to me I remember something, way back when, about the settings of the limit switches in Mach3 that could affect Z-axis drift...
Chet

Does the Z DRO show this movement?
Hood

Yes! I was surprised to see it, but the Z-axis numbers change on the readout... even thought they are not supposed to...
But, I am embarrassed to admit, I forgot to notice whether the program is actually calling for that change...  Rats!
I'm using Acme Profiler to generate the code, but it theoretically shouldn't be generated the shift...

Okay, I got lucky...
I have a program running and it allowed me to see the drift in action...
The Z-axis readouts show the drift with changing numbers, but the programming code does NOT call for any change.
I look forward to your analysis...

Can you post your code and I will see if I can get the same in simulation. Also if you could attach your  xml if it has changed from the last time you posted it.

Hood

It's a kind offer, Hood, but it's 56,000 lines of code.
I'll hold off on sending the file for now.
Let's see if someone else is having the same problem...
I'm sure I read about this a year or so ago when I was just getting familiar with Mach3...

One more observation...
The Z-axis is stable during the duration of a Depth of Cut...
It is only drifting during the duration of a Height of Clearance...
Both are arbitrary commands set by the programming code.
Why would one be stable and the other unstable?

Afraid with out being able to replicate it here I am out of ideas.
I have tried with your xml and it seems fine but without trying with code that you definitely get the problem with its not possible to say whether its a hardware, software or config issue.
 I understand you may not want to share the code for many reasons but if you find some simple code that also causes problems for you please post and I will see if I can replicate it.

Hood