TPU was good now not so good

I bought the J1s for TPU and it’s been great so far. The last two prints I have had to stop ( I had previously printed the same files no problem). Now the extruder clicks and skips but it doesn’t clog, it just misses parts of the print… it looks like its eroded somewhat.

Details of the filament and setup
I am using Sainsmart 95A
Its dry at 18% humidity in a dry box on a shelf above
Filament is fed in direct from the dry box with very little resistance ( lid is removed from J1)
Using Prusa Slicer
Speed is 35mm for all parts retraction is 1.2mm and temp is 220, layer height 0.12
Z height is perfect, machine recalibrated after first time it failed.

Things I’ve done
Tried running it hotter ( 220 normal, I had increased to 235)
Tried increasing the Z height while watching first layer squish
Have tried to tighten the grub screw on the extruder gears one was a little loose but not much at all.
Have ran PETG through to flush and the extruders doesn’t click with PETG. Cooled it down and attempted a cold pull at 180
Have opened up inspection gate and no build up on gears

The sound is a constant tick like every half second. Now even when the hotend is away from the build plate and loading at operating temp ( 220) and at 250 degrees

The machine is only a couple of weeks old, do I still have the old problematic hot ends ?
Is it possible that the more I have used this, that the resistance of the filament against the PTFE tube is increasing like not sliding against the inner walls as well as it would at brand new ? Could this be a result of heat creep ?

I have 5 other machines running TPU all day every day with all metal hot ends ( microiswiss NG’s and Sprite extruders)… would the soon to be released all metal hotends fix anything ? Or is the problem the distance between the gears and the hotend… like a semi direct drive as such.

Seeing IDEX is the only possibility of fully automated multi colour flexibles in that super competitive price range, you would think Snapmaker would double down on catering for flexibles if the length between the gears and the hotend is the problem allowing the filament to compress and expand over that distance… should that be the issue.

Please help… TIA.

Check J1/J1s Clogging Issues and New Hotend Kit Update and see if you got the old hotend, also maybe try to loosen the grub screw instead and see if that helps. You can also take the plastic covers of the extruder housing off to see if dust got into the filament path causing resistance.

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Thank you of the reply… I have seen that thread, I can’t tell the difference between the new all metal hot end and my one, but can’t see the difference between the regular hot ends and the one that came with the machine. I can try the grub screw, it can’t hurt, but why would it only do it with TPU and not PETG ? I will take the covers off and check them out too. Before I go pulling things apart, do you or anyone know if the PTFE tube in the hotened is accessible ? just looking at eliminating some of the causes mentioned in the thread you linked.

There is no PTFE in the hotend as the J1 is full metal. The new J1 hotend have a conical profile from the block all the way to the nozzle where as the old hotend have a standard V6 profile (cuboid). Some TPU does not do well when pinched by the extruder while PETG being a much more rigid material does not suffer from this.

I understand that regarding pinched filament… but why the clicking? That pinching or squashing on my other machines can affect the esteps, but it doesn’t affect anything else.

I am a bit confused about the hoted not having PTFE… why do they refer to it as being one of the known issues in the thread you linked… and why do they offer an all metal hotend if they are all all metal hotends ? The comparison chart refers to PTFE tube as well… Apologies if I am missing something here.

That’s not quite right.

My hot ends have a small PTFE hose in them.

You can get to it by unscrewing the metal connection at the top of the hot end.


oh right sorry I forgot as I modded all my hotends to be completely full metal oops


As per my knowledge, You can follow few additional things to consider:

  • Ensure that the tension on your extruder is not too tight or too loose. Too much tension can cause the filament to deform, and too little can cause it to slip.

  • Even if it looks fine, the PTFE tube might have developed some internal wear, which can increase friction over time. Try replacing it to see if that makes a difference.

  • TPU is prone to heat creep, which can soften the filament before it reaches the nozzle, causing it to jam. Make sure your cooling fans are working correctly and consider adding additional cooling if necessary.

  • Since your other machines with all-metal hotends handle TPU well, upgrading your J1 to an all-metal hotend might help. This would reduce the possibility of heat creep and improve overall filament flow.

  • TPU can be sensitive to retraction settings. Try reducing the retraction distance and speed slightly to see if it reduces the clicking.

  • Ensure the filament path is as smooth as possible. Any additional friction can cause issues with flexible filaments like TPU.

And also check this : given your setup and the adjustments you’ve already tried, upgrading to an all-metal hotend might be the most straightforward next step. It could help mitigate some of the issues you’re experiencing with TPU.

I hope this helps!

Respected community member!

Thank you @chitramishra that’s great advice. I have been leaning to the possibility of some sort of resistance between the nozzle and the extruder gears. I have already ordered the all metal hot ends in an attempt to mitigate both heat creep and a potential problem with the PTFE lining. I have Capricorn Bowden tube here, I will attempt to replace it with that and keep those hotends as spares.
I would love for it to be slicer settings, but I think given the distance between the gears and the nozzle, the length gives TPU more stretch than other direct drive extruders and 1.4mm at 25mm/s still gets some cobwebbing, but it’s very tolerable. Next step with that would be slowing the down to 25mm/s print speed to then try and help the retraction recover.

I will report back when the new hotends are installed in case others are here to investigate a similar problem.

I need to ask… is there a way to adjust the tension on the extruder gears ? I can’t see anything obvious where the passive gear is attached to the inspection door. The tension plays a big part with TPU on my other machines. I have not pulled the hotend apart yet, the machine is only a week old.

Is this the sort of lack of thermal paste that could cause the problems associated with this thread ? I have replaced the hotends with the all metal hot ends and will report back after a few prints, but in the meantime, I would like to rebuild the original hotends as spares. The PTFE lining was cut straight and had no signs of wear.

@mehlawlarz is there a drop in part to convert these to all metal ?

Yes that does appear to be one of the hotends with less then ideal thermal paste especially near the heatbreak where its most essential, sadly no there is no direct drop in part unless are willing to cut some metal then you can get a extra long MK8 heatbreak and cut it to size or go the route I have outlined here where you use a normal mk8 heatbreak with a volcano adapter.

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Can report back that the all metal hotends have made a huge difference and I don’t get any clogs or under extrusion. The erosion was under extrusion but the hot end is a lot better for consistency and quality. I now run Orca and used their flow calibration tests which are excellent ( highly recommended if your here researching TPU and the J1S)… the standard flow was way way off for TPU and was no doubt contributing to part of the problem.

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Get the new Hotend. Much better. Pressure Advance values are better too.
No clogging when you print multi color or different materials anymore.

The old ones are not good…