I’ve built 2 printers now, a Dolly and a custom i3 design using 2020 extrusion for a frame. On both I use an inductive Z probe for bed leveling (and have no experience with any sort of manual bed leveling). On both printers, I’ve found that using a 4x4 bilinear auto leveling setup has always produced inaccurate results. Whenever I print a relatively long part (100mm+) there is a clear difference in the print height when looking at the bottom of the print, and sometimes it is so pronounced that the print won’t stick to the bed at one end at all.
Both of my beds probe at about a 1mm height difference at the extreme corners. I do see the z axis moving while it is traveling along X and Y, so the compensation seems to be working. On the first printer I manually measured the Z probe offset, but on the second I designed the X carriage myself so I was able to use the exact measurement from the design. In my gcode I don’t do the bed leveling until the bed is fully up to print temperature, to account for any warping under heat.
What, if anything, can I do to increase the accuracy? I’ve only tried bilinear and only tried 16 points so far, it didn’t seem like any of the other styles would be of much help and 16 points is already quite a lot for a 200x200mm print area.