Problem with Z work offset on lathe

Hi guys.
So I have CNC lathe Numco Kc6, running on Linux Cnc.

I'm experienced on manual lathe and Haas CNCs. But I'm pretty new to linux, I've been playing around with it for a month now.

I'm running my second batch of parts, the first one was without a problem, but this second one keeps bothering me for two weeks.

The problem: My Z work offsets aren't holding their position. The part blanks are the same length, but when I load the part in the chuck and start the program... The facing cut just starts like 3mm from the blank.

So do you think this is problem in the software or in the machine? Because sometimes when I home the Z axis it seems to help, but I don't want to home Z axis every time I change the part.

I have a drilling cycle in program, so I'm kind of thinking if the drilling of 22mm hole might be to much force for my cnc and it somehow shifts axis position. Because during the drilling cycle I noticed the drill does few empty pecks before it's drilling material again...

Thank you for your answers in advance.

Thank you for you answer.

Yes, my cnc uses steppers.
So my gut feeling was right the drilling is just too much force on the steppers... I'll try predrilling the parts before moving to the 22mm drill.

Thank you again, you might just saved my starting business.

Hey, so i tried it and it works.

Thanks again.

No problem.
But now I want to fix another problem with my limit switch... So never ending battle I guess. I even tried looking for professional CNCs, but they are way over my budget.

If you're interested in my limit switch problem I posted about it a few minutes ago.

Anyway thank you again.