Hey @Tone, i wanted to share my dial-indicator results with you (A350, 5x5 grid):
The heatbed itself is uneven itself, it compenates a bit while heating.
Heating for 30min vs start printing right away after heating, difference of the points about 0.01mm to 0.2mm.
Heating for longer than 30min (60min) brings no more essential expansion to my heatbed, ~0.02mm.
heated bed without print sheet:
cold difference MIN/MAX: 0.86mm
hot difference instant printing MIN/MAX: 0.64mm
hot difference 30min heat MIN/MAX: 0.68mm
hot difference 60min heat MIN/MAX: 0.70mm
heated bed with print sheet:
cold difference MIN/MAX: 0.82mm
hot difference MIN/MAX: 0.65mm
Everytime the lowest point of my bed is I1J2.
My highest point is I4J4.
All in all the heat bed is massively warped.
From point to point in a tri or rectangle it seems not so much (except the front left edge), here the values vary about 0.04mm - 0.2mm.
I would love to hear more about the problems from the snapmaker team, like prusa did it in this blog:
It seems this is a problem of every 3d printer company.