I have an Anycubic I3 Mega which I am adding an IR sensor to in order to calibrate the height of the Z axis. All working well, however the Z home position is 2.5mm above the bed, so I need to lower the Z axis by 2.5mm.
Reading up on this subject provides details for using the G92 and M851 gcode. I have reflashed the firmware with Marlin 1.1.9 and whilst that update worked as expected, using G92 or M851 doesn't seem to work.
I notice on the S3D FFF configuration dialog contains a section for global G-code offsets. Does this offer the required definition for offsetting the Z axis? In a quick test this doesn't seem to work as expected, though perhaps I'm not using it correctly. Suggestions welcome.