Dug out my old 2.85 TPU stash and got it running on the U1

Same boat here, I had a couple of 2.85 rolls of PLA and PETG left over from an old Prusa i3 clone that died years ago. I mostly run 1.75 on everything now so they just sat in a bin collecting dust. When I got my U1 I figured the larger diameter woud be a pain but it turns out the extruder handles it fine as long as the path into the inlet is smooth.

What made the difference for me was swapping in a longer piece of PTFE tube with less of a bend right before the feeder. The stock routing had a tight corner that the thicker filament kept catching on. Once I gave it a gentler sweep it fed clean for hours. I also printed a simple guide block that mounts near the spool holder, nothing fancy, took two tries just like yours.

For anyone thinking about trying flexible material, my only tip is to slow way down. I printed a hose adapter in TPU at about half my normal speed and it came out fine. The faster attempts were stringy and the extruder skipped now and then. Honestly the older 2.85 spools I have seem drier and less brittle than some of the 1.75 stuff I bought recently, so they are printing better than expected. Might be worth checking what is actually in your spares box before buying anything new.

Funny timing reading this, I did the opposite with my leftover 2.85 stock. Had about five spools of assorted stuff, mostly PLA and one nylon, left over from an old Ultimaker clone I built years back. Instead of adapting the U1 to take them I just kept the old machine running in the corner for exactly that purpose. It's ugly and loud but it eats 2.85 happily, so the spools still get used up on draft prints and shop jigs while the U1 does everything I actually care about. That said, your bracket experiment makes me want to try something. My gut says the TPU angle is the hard part, since flexible filament tends to bulge and jam anywhere it can wander sideways. On my old delta I had to print a guide almost identical to what you describe just to stop the TPU coiling up behind the extruder. Rigid 2.85 was never a problem, soft stuff always was. Do you notice any difference in how the feeder grips the thicker filament? I always figured the gears on these newer extruders were cut for 1.75 teeth spacing and 2.85 would slip under load. If yours pulls TPU without grinding that's a better result than my old machine ever managed, that thing chewed through flexible filament constantly.

Still figuring out wheather I even qualify to post here since my U1 only showed up last week, but this thread is useful timing. I've got one ancient 2.85 spool of ABS in the loft from a printer I barely used, and I'd written it off completley. One thing I'm unsure about though, does the angle of the guide bracket matter if the spool sits above the printer on a shelf instead of on the stock holder? Mine would be feeding from a diffrent direction entirely and I don't want to warp a bracket guessing at it. Might just print the first version and see what happens.

Update: the person asking about the entry angle, yes it matters more than I thought. I tried running my bracket at a shallower slope and the filament fed noticeably smoother, almost no friction at the guide. Also, seeing that some of you kept an older machine around just for 2.85 stock made me reconsider, but my bracket is cheaper than the electricity bill for a second printer, so I'm sticking with this for now. Next test is one of the stiffer leftover spools to see if the gentler angle fixes those too.