I’m having an annoying issue with the H2D in that it just keeps jamming with TPU. Even when manually loading a single piece of TPU directly in (not pulling from a spool etc) and not having the hotend even attached, it will still jam in the gearing.
I’m not using TPE and it’s a fairly firm TPU, around 50D. I’m suspecting that the gear tension is too great and the TPU is being squashed in to an oval shape which then causes it to not pass through the circular filament path and then the motor clicks and I get the dreaded: “The extrusion resistance is abnormal. The extruder may be clogged or there may be filament stuck in the toolhead.” message.
It’s complete luck if a print completes, sometimes the prints are perfect and I don’t get the message once, but other times I get this message constantly or just half way through a print. Sometimes I can pull out the filament, cut off the chewed bit and resume but most times I can’t.
My filament has been dried correctly and my Max Volumetric speed is now at 3mm/s but still it jams. It’s driving me insane, is there a way to reduce the gear tension as I think this might be the issue.
Any other suggestions that might fix this? I have more than one H2D and they are all doing the same.
I don’t have experience with D50, but it being harder and stiffer than A95, which prints perfectly, it might be that the shape doesn’t return (fast enough) to it’s original round shape.
You might want to try a larger nozzle diameter to reduce the resistance a bit.
A thorough check of the filament path would be good to do also.
Are you printing with the left or right nozzle?
Besides that I don’t know what else could be done.
I’m printing with a 0.4 nozzle on the right side (I think that’s the correct side for TPU)?
Even without a nozzle attached and just feeding a piece of TPU manually, the gearing will skip though which tells me that there’s something fishy with the tension (all my printers have the same issue, the path is clear as I’ve dismantled the heads so many times to remove bits of TPU and clean the gearing etc).
I didn’t have this issue as much on earlier firmware but then it was also cooler a few months ago. Ambient temp is about 20 degrees here, usually it’s around 10 degrees, not sure if 10 degrees extra ambient would be enough to soften the TPU enough to cause issues but it’s a thought.
I’ve adjusted the retraction/de-traction speeds but it will jam even when loading manually with a free piece of TPU and no hot end. Pressing the down arrow to feed the TPU with most of the head dismantled, it will just jam and skip in the gears.
I can’t seem to see any way to adjust the tension unless Bambu release a TPU spring as it looks like it’s a fixed spring between the hotends that keeps the tension.
The motorised cam that switches the heads I suppose could be used to reduce the tension by rotating a set amount and restricting the spring from clamping fully on the TPU, but I’ve not idea if there’s GCODE that could be used to experiment rotating it, I’m doubting it.
I guess Bambu might have to add it as a feature, a few pre-set tension amounts for softer filaments maybe?
What I think you should check first is the temperature—if it’s set too low, it will immediately create back pressure and lead to some form of jam. I print TPU 95A HF (auto-loaded), TPU 90A (semi-auto-loaded), and of course TPU for AMS, which is 65D. Also check your PTFE paths; even the slightest resistance will be amplified during printing and can result in jams and poor print quality.
Just to clarify our definitions: TPU 50D is significantly harder than both 95A and 90A, which I regularly print on my H2D. For reference, 95A roughly corresponds to about 46–48D, which shows how much stiffer 50D actually is.
Most likely then you might have a stray piece of filament in the extruder gears. Remove the “filament guide”, its the lower portion of the extruder cover and inspect things. Its only a few screws, pretty straight forward.
I’ve dismantled the entire head and checked all paths. Cleaned all the gearing etc with a stiff brush to remove any TPU residue. Same issue for two printers currently.
I’m running latest firmware, part of me thinks they’ve changed the sensitivity or torque on the gearing in newer firmwares.
I would then inspect the extruder gear and arms… check for concentricity and any defects. I print a lot of TPU and yet to have a problem on H2D. Generic and bambu 90A and 95A.
If you load PLA, PETG, or another material, does it also skip? It would be highly illogical for your TPU 50D alone to fail feeding through a completely clean and unobstructed extruder, since many of us print TPU in nearly all hardness grades. My suspicion is that there is simply some debris in your extruder’s feed path.
If you are confident there are no filament residues stuck in the gears, I would suggest increasing the nozzle temperature to 260 °C while loading. After using TPU, I purge my nozzles at 300 °C and run cleaning filament through them. If the extruder grabs and feeds your filament and you see melted TPU coming out, it means the previous loading attempts were made at too low a temperature.