Kossel linear plus: tuning a poor mesh grid

[gtrevi]

Hello all,

I'm struggling in trying to fine tune my Kossel linear plus printer.
Prints are coming out fairly good, but I'm getting out this "not so good" heatmap, with a corner bent down 0.216mm:

0_1550002324969_heightmap.csv

The whole printer is maniacally squared and leveled against the all metal CNCed corners (even carriages & head are metal).
The levelling probe is an original BLTouch.
The bed is a 240x4mm borosilicate glass disk, directly laying on the 3 lower-top 2020 aluminum extrusions, so absolutely flat and therefore I cannot understand why I’m getting this convexplane... which is btw pretty much compatible with some warping of the prints in that "blu" area.

Can anyone suggest what can I possibly look after, as I totally ran out of options here? 😊

Thanks for any help!

[Veti]

http://boim.com/DeltaUtil/CalDoc/Calibration.html

looks a bit like Tower Placement Symmetry

[gtrevi]

@Veti thanks for that resource, really interesting article.

Not sure though it's a symmetry problem, as mentioned the whole printer is maniacally squared and leveled against the all metal CNCed corners & 2020 profiles... moreover, everything is assembled with proper chuncky T-nuts (not those useless square bolts).

Could it be perhaps be a slight rod/radius length difference (looking at the article you pointed out)?

[Veti]

What is the number of calibration factors that you used?

[dc42]

My guess is that you have a geometric error that is causing effector tilt when the effector is is the blue area. Mount a circular spirit level on the effector to check this.