X-Axis Rod Spacing  

X-Axis Rod Spacing

I finally spent some time to verify a suspicion.  It seems the X-Axis rods are not as precisely aligned as we'd probably like, and this is causing some of the X-Axis self test errors by increasing drag that shouldn't be there.

The crux of the problem is the two X-Axis support brackets are printed vertically, so the rod spacing side to side is relative and virtually identical, controlled by the lead screw precision and layer one - 44.934 mm on my Mk3.  But, on the extruder, the bearings are held in parts printed such that the bearing spacing is controlled by X or Y axis calibration, which is not as precise as the lead screws. On my printer, the bearings are held at a spacing of 44.705 mm, which causes them to bind as the extruder moves closer to the brackets. A 0.229 mm crunch. 

This issue can be amplified at Prusa's print floor when parts for X come off one printer and the extruder comes off a different printer. 

A solution would be to have the extruder redesigned to allow the lower bearing to float vertically a +/-10 thousandths. The top rod and dual bearings will carry the weight or the extruder and X torque, the bottom bearing the Y torque that is applied during printing. 

I suspect Y has the same generic issue, but the rod holders probably have enough slop the issue isn't as pronounced as to cause added friction.

I started looking at the extruder drawings to see if making the lower bearing cutout oblong... but there are hardware cutouts, nuts and screw ends... so not sure if a mod will work.  So I am wondering if anyone else has worked through this and come up with a solution.

The alternative is to just reprint the extruder, but change the scale to better match the X-Axis supports... but this may also have problems if the materials aren't identical and thermal stability causes binding. So it looks like a reprint of everything. Lol.