Tronxy P802D X Belt Tensioner - parametric

NOTE: I completely redesigned this!

1. belt alignment is slightly out, I can't bring the pulley on the stepper any further forward without the belt rubbing on the front wall of its slot in the left Z-trolley, so I moved the axis of the cable pulley hanger slightly backwards, off-centre,

2. Because of the big-assed bearing (a 6x20x5) used for the right-hand pulley, there were some adhesion and sizing problems on big jobs at the extreme-right (no, not alt-right ;-) of the x-travel, so I used