I have a cheap bedslinger, an Anycubic Kobra 2, and generally it's a pretty decent printer at the price. I have flashed klipper FW on it, so I'm not using Anycubics FW.
I have issues whenever I try printing bigger parts, the first layer is always complete shit (see post photo).
Heightmap, measured with inductive probe
range is only 0.085mm from min to max, so it should be reasonably flat. The heightmap is automatically recalibrated and loaded as part of my print_begin macro.
Slicer settings for line width
I don't know if my printer just doesn't correct Z-height during first layer, if my line width settings are completely messed up or what is causing this, but the issue is only apparent on bigger parts with large contract surface on the bed.
[SOLVED] It was just Z-offset that was too low causing this. however when running the calibration routine from ellis3dp on first layer squish, the settings that looked good on the small calibration patches, looked like crap on bigger prints. I needed a bit higher Z-offset, but that solved it.
As mentioned in the OP, I'm running klipper. Yes I can microstep it, but I haven't been able to find a sweetspot where it all looks acceptable.
The good news is that you're running Klipper, so you can tune this very easily.
Go download a first layer patch from Ellis and use his guide as a reference.
The idea is to place 10 or so on the bed and adjust your z-offset on the fly until you get it right. Once you've found the correct amount update your printer.cfg.
PLA wants a small amount of squish. If you run your finger over the surface it should feel smooth. If you feel the ridges you're too low. And if it is wavy you're super low.