while squaring XY I aligned with the front plates. Not even a hair fits in both sides. Still when cutting a 70cm T into a waste piece and check with a long square, the assumed right angle is off ~4mm at the bottom of the T. Basing on this I would need to shift back corner left. I assume this would get my frontplates misaligned again.
Could you please give me a hint where to look for a detailed instruction? I found https://www.shapeoko.com/wiki/index.php/Calibration_and_Squaring_the_Machine. This honestly looks comprehensive but more like a bulletpoint list not really indicating to me what to do in my case and my low experience level with the S3.
What would help me is a you measure this, do that kind of tutorial. Maybe there is something like this out there?