TPU /flex curl and jam in Nextruder
Hi.
I've got a problem I can't seem to solve. I've got a MK4 with the Nextruder and this modification to the idler lever. I'm trying to print TPU with Shore 95A hardness but it always curls up and jams in the Nextruder. See attached image of what I mean. I've always used the generic flex profile in Prusa Slicer and tried:
- Generic flex profile - Fail, in-extruder curling and jam.
- Loosened idler lever screws with 1½ turns - Fail, in-extruder curling and jam.
- Loosened idler lever screws with 3 turns - Fail, Nextruder has such a weak grip on the filament that it eventually just stops feeding filament because it can't get any grip on it.
- Loosened idler lever screws with 2 turns - Fail, in-extruder curling and jam.
- Loosened idler lever screws with 2 turns, changed retraction length from 2.5 mm -> 2.0 mm - Fail, in-extruder curling and jam.
- Loosened idler lever screws with 2 turns, changed retraction speed from 60 mm/s -> 25 mm/s - Fail, in-extruder curling and jam.
- Loosened idler lever screws with 2 turns, changed retraction speed from 60 mm/s -> 25 mm/s, changed retraction length from 2.5 mm -> 0.5 mm - Fail, in-extruder curling and jam.
- Changed retraction speed from 60 mm/s -> 25 mm/s, changed retraction length 2.5 mm -> 0.5 mm (tight idler lever screws) - Fail, in-extruder curling and jam.
I'm kind of running out of ideas here with what to do. Does anybody have any advice to share?
RE: TPU /flex curl and jam in Nextruder
Missing adding the modification, it's this modification I've got. https://www.printables.com/model/596608-nextruder-modified-idler-lever?lang=de
I added this modification after my stock idler lever in PETG probably experienced some creep and didn't grip on the filament as much anymore.
Some more info: I am hesitant to think that the problems I have is due to the idler lever screw tension. I lowered the tension until it barely could grip the filament at all, but that's not how it's supposed to be. The nextruder needs to be able to grip the filament. So I am leaning more towards it being some issue with the slicer settings, but I don't know, I've never printed with TPU before.
Finally, I've never had any problems loading the filament successfully, all these curls and jams come after about 5-10 minutes of printing.
RE: TPU /flex curl and jam in Nextruder
Reduce your retraction. I had the same problem. The filament sensor reduces the ability of the filament to escape back up the tube, so it has nowhere to go other than to curl up. If you get enough of a curl it jams the assembly.
RE: TPU /flex curl and jam in Nextruder
Reduce your retraction. I had the same problem. The filament sensor reduces the ability of the filament to escape back up the tube, so it has nowhere to go other than to curl up. If you get enough of a curl it jams the assembly.
I just tried turning off my retraction completely and doing two test prints, one with the idler lever screws tight and another with them loosened. Both of them resulted in a curl + jam, but this time at the bottom of the nextruder instead of at the top (as in the picture).
Even if it works for you, we really shouldn't have to resort to that, especially when printing a moderately hard TPU like 95A. Seems like it's going well for others with the same machine, but not with ours! Having retraction is important, otherwise everything's a big stringy mess.
RE: TPU /flex curl and jam in Nextruder
Do you use a tube to guide the filament? If so take it out or at least disconnect it, so the retracted filament can go up freely. A tube can add greatly to the resistance the filament sees. Your 95A is about the same hardness as the 40D that I use without any problem, and harder than the Varishore I print with the MK4, also without problem.
I use both with the setups Prusa recommends, so it is sloooow, but it works. Also I always do a coldpull before loading the flex.
Aftrr reading another post on this forum: maybe check/clean the rest of the filament path and the sensor. It could be there's some debris there.
Last but not least one thing that crossed my mind: did you print a lot of abrasive filament like metal or stone filled? If so this may have worn, opposite to the filament sensor, the coating in the channel and left a rough surface.
I addressed a similar problem a few days ago in:
Cheerio,
RE: TPU /flex curl and jam in Nextruder
Do you use a tube to guide the filament? If so take it out or at least disconnect it, so the retracted filament can go up freely. A tube can add greatly to the resistance the filament sees. Your 95A is about the same hardness as the 40D that I use without any problem, and harder than the Varishore I print with the MK4, also without problem.
I use both with the setups Prusa recommends, so it is sloooow, but it works. Also I always do a coldpull before loading the flex.
Aftrr reading another post on this forum: maybe check/clean the rest of the filament path and the sensor. It could be there's some debris there.
Last but not least one thing that crossed my mind: did you print a lot of abrasive filament like metal or stone filled? If so this may have worn, opposite to the filament sensor, the coating in the channel and left a rough surface.
I addressed a similar problem a few days ago in:
Cheerio,
Thank you for the tips. After a few weeks TPU vacation I'm back at it again. I've tried a few prints without the PTFE tube. Now I'm always facing the same problem, that the filament curls up and jams at the lower end of the nextruder (towards the nozzle). Seeing as it's curling towards the lower end, that suggests (at least to me) that it's not a question about retraction or PTFE tube but rather something about the filament being too soft to overcome the pressure needed to push it through the nozzle. Or that the heat from the nozzle creeps up and softens the filament so much that it just buckles when being pushed downwards.
Does anybody know what settings (preferably just in the filament settings) I might change to counter this issue? (Right now I'm using the Prusa Slicer Generic Flex filament settings)
You probably need a little bit of tension to pull the filament back as it retracts - but not as much a you get from the friction inside the tubes.
I really must look into a proper solution but I keep my old Mk3 for printing the majority of TPE jobs and only use the XL for mixed material work.
I have had some success with light braking and also with hanging a travelling weight (from the fishing tackle box) in the centre of a loop of filament to maintain consistent tension. To date these have been improvised as required but perhaps could be formalised into a project ... hmmm.
Cheerio,
RE: TPU /flex curl and jam in Nextruder
I've finally seemed to have solved it.
I tried with and without the bowden tube, it didn't have an impact. What I did was find a good combination between printing temperature and extrusion multiplier (even changing just a few percent could be the difference between a complete jam and fail and not).
I didn't need to do anything with tension.
RE: TPU /flex curl and jam in Nextruder
Nevermind, the curling and jamming is back. Must have been just a fluke that I managed a few prints without that issue. Hm. What a bummer.
RE: TPU /flex curl and jam in Nextruder
What speeds are you printing at? I print tpu on my MK4 & XL regularly. I set the volumetric flow to 2.5 and nozzle temp of 220.
Initially I had some jamming issues, but raising the temp, minimal retraction of .8mm, and slower speeds had led to great results. Almost no stringing with dried TPU.