I finally tried something that actually had a significant effect…
I wrapped electrical tape onto the idlers with the teeth riding the smooth face.
I couldn’t believe it had worked so I unwrapped it and tested again, then rewrapped it two more times. Consistently it improves the surface and seems to do so a little more when it is loosely wrapped.
There is some increased friction as it passes over the area where the tape overlaps itself an inconsistent number of times, but every test was superior despite that. On the first test I believe slight ridges where the tape wrinkled imparted a cyclical pattern to the print so there are a few lines that stand out where the standard 2mm have reduced.
Images show everything standard vs the first time I wrapped it with tape.
Images with the notches on the corner are the exterior shell printed counterclockwise.
No notches are the interior shell printed clockwise.
The faces with an R are the rear side and the sides facing the Y axis are not pictured but seem to be slightly better though it’s harder to say since they were not too bad to start with.
I think what this points to (despite people saying they tried it and saw no improvement) is that the teeth on the smooth pulley is indeed problematic. It is still possible that it’s the teeth rubbing the flange or just the teeth on the smooth surface in general, and this still doesn’t explain why some printers are really bad and others are fine unless some of the early bearings could be performing really poorly.
The three permanent solutions I have in mind:
• Add a soft rubber sleeve to the existing pulleys. Maybe a stretchy silicone tube.
• Make a firm but somewhat flexible toothed pulley (like polyurethane or one of the FormLabs flexible sorts of resin) since I can’t find any such thing on the market.
• Replace the existing pulley with a toothed version in plastic or standard aluminum.
What I am not looking forward to is that while the left pulley appears to have a bearing shaft that drops out the bottom, the right side shaft needs to come up and there’s part of the printer frame in the way. Unless I’m missing something the entire X axis has to come out to change these bearings and I am not looking forward to that.
If anyone has done the X-axis swap or pulled those idlers and has pointers or any shortcuts, please share!