@twinkler said in Mesh leveling for large bed:
No matter what I try, I cannot get it to properly compensate the lack of flatness in my bed.
Your heightmap shows a total vertical error of over 2mm.
I'd suggest you check things just with a straightedge or ruler to see how much curvature the bed and X axis rail really have, with the head somewhere around the centre of the X travel to give a "worst case" load.
If there is really that much distortion somewhere, any large print you do will have a curve with a 1-2mm recess in the middle; you will never be able to get a flat base on anything.
I had spurious probe errors on one of my machines, showing significant bed distortion that was not really there (using a BLTouch).
I did a low point count heightmap then edited it to zero at all points, so there was no compensation, then after restarting the machine and a G32 to level the bed, checked Z clearance at multiple points using a plastic shim as a gauge piece between the nozzle and bed.
The probed heightmap was totally wrong, compared to actual measurements.
I tried it with a simple precision switch type probe and that gave a completely different and near flat heightmap, which worked fine.
I've still not got to the bottom of the BLTouch stray readings, but the machine works fine with the other probe heightmap so I've not spent much more time on it.