Hello,
since I have my P1S, I had issues with putting grids in 2 axis together. A test print with a 200mm long angle (90 degree) showed a deviation of 0.9mm, which is =~ 0.26°. Bambu support suggested the xy-belt-tensioning procedure among 2 other recommendations.
After checking the 2 reference points on the backside of the printroom, they deviate by 1.5mm in my case. So using these, would lead to another not rectangle setup. After adjusting one side with a stack of tape to level both sides, the results after the belt-tension procedure is fine.
The printer itself doesn’t have a design, which would guarantee reference points, which are on the same line. So it seems, that this could be a general issue.
