I just installed my BLTouch clone (Marlin 1.8) on my Anycubic i3 Mega Ultrabase and finding confusing information about the
Z_PROBE_OFFSET_FROM_EXTRUDER or the
M851 command does the same as
Z_PROBE_OFFSET_FROM_EXTRUDER in the Configuration.h. (see marlin docs)
So according to Marlin, this value is the distance of the nozzle to the distance of the triggering point of the sensor.
If I manage to measure that accurately, Marlin could probe the bed, knowing distance of probe to nozzle, add a margin for perfect distance (around paper thickness) and my bed would be forever perfectly measured with every autolevelling process and perfect distances could be calculated.
Instead, I find tutorials around the
M851 (e.g here telling to manually level the bed, then take the current Z-value of the extruder and put that into the
M851 value. In my understanding it makes little sense, as it has no reference to when the sensor triggers, its distance to the bed.
Sure, maybe this way it can get an understanding of slight derivations in the planarity of the bed, but it would not have automatically "levelled" my bed, just compensated for imperfections.
I am confused by the amount of tutorials that suggest so. Whats the case now? Is Marlin not really able to really level to my bed?