ShoreA 95 TPU and MMU2 Success - Somewhat
I have modified my MK3S and MMU2S to get a successful print using PolyMaker PolyFlex, which is about ShoreA 95. I had to take the following steps:
1. Redesign the pulley base for the MMU2 to reduce the clearance between the housing and the pulleys to about 0.2 mm while maintaining the filament entry and exit angles.
2. Eliminate every catch and drag point between the detangler and the MMU2.
3. Tune the FINDA and IR detector positions using a sample of the TPU to get them to recognize the filament loaded state correctly.
4. Designed and installed a version of the TZB3 extruder housing that allowed the filament to be supported through the entire filament path. I did this by designing around a flex filament insert pulled from an old extruder from my Robox printer. The insert is a little hourglass shape with a 2mm hole through the middle for the filament to pass. The cutouts on the side allow the feed rollers to touch the filament.
Issues:
Adjusting the filament detection takes a lot of fiddling to get the detection and the tension on the extruder door just right. I did the LED modification on the IR detector to make it easier.
Ejection is difficult because the filament detector usually gives a false positive and the printer thinks the filament didn't unload properly, or the force on the filament isn't enough to pull it out of the nozzle.
Improvements:
1. Change the feed rollers to a straight tooth instead of the cut-in tooth. This will give more flexibility in the filament detection and will give larger drive forces. I haven't found straight cut feed rollers yet though.
I am going to keep testing when I have time and if I find anything more I can update.