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.
Just to comment a bit:
I think this is one of the casualties of "the paper method" being so poorly defined (because oldhats gotta gatekeep the hobby). People eventually learn WHAT the paper trick is (lower the nozzle until you can JUST slip a piece of paper between it and the bed) but not the next step which is to then step back "one step". Which.. also can end horribly because different printers have different dZ and people forget that their layer height is generally O(0.1 mm). So if you are doing 0.2 mm layers and your nozzle is 0.05 mm from the bed...
When I was learning I definitely made that mistake. Had poor bed adhesion and eventually learned about The Paper Method. Did that and thought I was smug and then... no prints worked and I had to clean my nozzle every time. Eventually found the last step and then looked at the number of what dZ was. Was useful because it means I actually understand how first layers work. Was obnoxious for all the obvious reasons.
Its why I really like that the more newbie friendly outlets and channels are increasingly suggesting using feeler gauges instead. That has other problems (people not realize there are error bars around that 0.3025 mm gauge...) but it provides a much more reproducible method (and can be semi-automated if you have a multimeter and some tape).