How does Z offset (M851) work with an auto leveling sensor? Does it add the Z offset to the offset of the G29 mesh? or the G29 value replaces the M851?
My printer is an Anet A8 with marlin firmware, I was having issues with the autoleveling sensor and reseted the z offset to 0 and let G29 get the mesh offsets and its working good now.
I was looking through marlin gcode page but couldn´t figure out how G29 affects M851 or viceversa.
My setup with level issues:
> M851 Z0 > G28 > M211 S0 ;turned endstops off and got a paper to find the zoffset > M851 Z-0.59 > M500 > M211 S1
And G29 before printing.
G29 determines the shape of the bed by probing the bed. This will set the shape of the bed with respect to the sensor trigger point. The z-offset is needed to set the offset between the bed itself and the nozzle with respect to the sensor trigger point.
The sequence to determine the offset is:
M851 Z0; // Set the Z offset to zero height G28; // Home Z in the middle of the bed G1 Z0; // This will move the head to zero height; M211 S0; // This will disable the end stops so that you // will be able to proceed lower than Z=0
Now adjust Z height to fit a piece of paper and note the negative Z height (either through the LCD or through an application over USB)
M851 Z-1.23; // Define the Z offset M500; // Store the settings M211 S1; // Enable the end stops again
Please note that -1.23 is a fictive value that should be replaced by your own value.