@kjiwa that depends on the layer height you want to use. My delta - which started life as a T3P3 Mini Kossel kit - routinely achieves less than 0.02mm and usually 0.01mm. I print using 0.2mm first layer height.
@kjiwa the idler should be positioned so that the belt passes over it at the same distance from the vertical tower extrusion as it it in the carriage. That way, the belt sections above and below the carriage will be in line even when the carriage is right at the top of the tower.
Ok,
Also I suggest you to verify those alignments.
Those must be at the same equal distance.
Doing this I reached that the X and Y of M665 are gone from several decimal to some cents.
In those trap we must gain as much precision everywhere 😰
In my case for obtain the more possible equal distance , I was not able to keep the tower aligned with the top frame.
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