I’ve had my U1 for a couple of weeks now and pla has been fine as you’d expect.
I mostly/at least half bought the machine for TPU and different material support capabilities though. I have a “product” I print primarily from 68D TPU (Bambu TPU for AMS) that I’ve had to print with regular supports and wanted to print a clean interface in PLA or PETG. This has worked brilliantly a couple of times on the U1, however…
The rest of the time, I’m getting TPU jams, it spitting the filament out sideways in the head. Even on single material prints. I’ve had issues with the 68D (AMS) TPU which I’ve never had a single jam on before. 72D and regular 95A. I’ve tried different extruders and I’ve now had to disassemble 5 times to unpick the filaments (this is not fun!). I’ve had more failures in the past 2 weeks than I’ve had in 5 years and I’ve not even been using it that much as it’s not my day job.
I’m really struggling to work out why I’m seeing so many problems. Filaments are dry, transfered to filament dryers and fed from there, a workflow that’s never been an issue before. Examining the filament I’m extracting from the downed toolheads it’s generally folded up and spat out of the side but not generally not that toothmarked, it just looks like it’s escaping more than anything.
Sorry I’m not gonna have much help, as I’ve yet to print TPU on my U1. Also, I’m unfamiliar with 68D.
One thing that did catch my eye is that you’re printing from the dryer boxes. While I understand that you’ve successfully printed that way in the past, have you tried printing directly from the U1 spool holder yet? Maybe there’s something with the U1 that has issues pulling from the boxes that will be negated with the spool holder…
Wish I could be more help and hopefully someone has more experience than I!
Thanks for the replies, I saw the first one in the middle of the night and then it occured to me that it’s occuring on retraction.
The toolheads I’ve disassembled which have been jammed, haven’t had the filament in the nozzle and I cannot be sure if I’ve seen the issue on a print when no toolheads have been swapped.
So, something about this particular setup is causing the filament to buckle on retraction. The 68D in particular really shouldn’t, it’s a similar stiffness to petg off the roll and generally prints as easily as pla.
Possibly too much resistance to being pushed back which is a puzzle as manually pulling it forward from the dry boxes feels lighter than the spool holders which have a fair amount of turning resistance. But in reverse, maybe this is different.
The other idea is possibly some heat creep softening the filament when another tool is being used. Again shouldn’t be the case, but it really has to be one of those two.
I’ve got 2 toolheads to take apart to unjam today so when I’m done with that I’ll try from the spool holders or maybe just removing the ptfe tube along the path. I think the reverse resistance is more likely the cause.
Incidentally, I was surprised how much space there is between where the filament comes in and hitting the gears. Even my old Artillery Genius’s extruder had the path extending most of the way… but it’s working for most other people so must be fine in this respect.Edit, I’m just being stupid here - the path is constrained on the piece you take off.
Oh the 68D will print fine on the racetrack beyond 18mm3/s in both the P1S and U1. But dropping it to 3mm3/s for normal TPU didn’t solve the issue.
Retraction wise, for the nozzle to be empty upon disassembly, something appears to be retracting it a long way on toolchange. The settings for the filament and profiles are normal though. I’ve tried my existing Bambu profile and generic TPU on both of these fronts.
Right, this looks like a problem of my own creation. I was butting the ptfe tubes from the boxes up against the inlets on the feeders, when pulling through, the resistance is fine and it seems to work OK.
When I push or pull the filament back though, the resistance is much higher.
This must be why mods such as this exist: PTFE adapter for Snapmaker U1 by Lukáš Komenda | Download free STL model | Printables.com
I have removed the ptfe tubes for now and will re-evaluate.
For TPU you need a trick: loosen the side screw a little bit on the print head to reduce gear pressure so the TPU can pass through the gears more easily.
