Anyone got a clue as to why I would suddenly develop Z ribbing that looks like a rounding error. I have double checked the threads and pitch is 1.25, replaced the stepper motor and driver, filament is consistent (from Ultimachine), and the results are the same with two builds of slic3r and whether or not I’m using volumetric extrusion. The ribbing does not match my thread pitch but the pattern is evenly spaced which is why I think it looks like rounding error.
ABS @ 241c
Speeds are all 40mm/s
No backlash and not too tight.
Verified threaded rods are not constrained and not pulling against the smooth rods.