Z-Axis "Lift and drop" while profiling

[The James]

Hi Forum!
I have an old AXYZ 4008 series CNC. Recently I have started experiencing a “lift and drop” of around 1mm on the Z axis while profiling parts.
A strange anomaly is that it seems to replicate at exactly the same point on matching vectors.
Tried using original Aspire 4 with different post processor and still experiencing the same issue. My next thought was to swap over drivers to see if there would be a difference.
The attached pics show for and reverse side of 2 identical vectors being profiled.
Any words of wisdom would be greatly appreciated.
Regards
Kevin

[4DThinker]

Check for anything that might be blocking your Z axis from travelling down in those areas. If it isn't something digital then it is likely something physical.

You can check the G-code with any text editor and look for the Z part of the commands. With a simple profile toolpath there shouldn't be much code to look at. if you find something unusual in the code please post it here.

[The James]

Bloody Lock screws behind Z axis plate came loose!! All sorted