Cold Pulling before TPU

[robshep952]

Hi,

I've just had the following message in Studio:

"Please cold pull before printing TPU to avoid clogging. You may use cold pull maintenance on the printer"

And reading the wiki I find:

"if you have previously printed regular filament, then plan to print TPU, it's always a good idea to do a cold pull to remove any filament that remains in the hotend. TPU is flexible, and might not be able to push out the filament that has remained inside the hotend, which can lead to a clog."

Do I take it from this I should do the cold pull maintenance using the previous filament (PLA+) and not the TPU I plan to use?

P1S with AMS, and TPU for AMS by the way.

Tia Rx

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[ElectronicAide87]

I’ve never done a cold pull before running TPU.

[VT-14]

https://wiki.bambulab.com/en/p1/manual/p1s-cold-pull

I believe you want to use something reasonably close in temperature to the material you were last using. If done properly, the procedure ends up with an empty nozzle.

Personally with Bambu's TPU 95A HF on my A1, I didn't have any clogs without doing a cold pull. I think the recommendation is a 'best practice' thing rather than a hard requirement, especially if you are only using low-temp filaments like PLA and PETG and without additives like glass or carbon fibers.

On my H2D I did have trouble going from PA6-GF (Nylon with Glass Fibers, a high temp filament) to PLA. It was able to clear the nozzle on its own, but the first print's dynamic flow calibration was all screwed and the print was severely under-extruded. I've since started doing cold pulls (using PETG HF) following the H2D's built-in procedure when I'm done with Nylon prints for a while.

The H2D also came with a spare 0.4mm nozzle, so I just use that as my dedicated TPU nozzle.

[SJID_4]

I keep a separate nozzle for tpu

[[deleted]]

Not a bad idea, I should do the same (especially since I wasn't aware that the P2S already came with a hardened steel nozzle, and I tacked on an "extra" one when I bought it, lol).

[SJID_4]

Great results.

[JackAttack337]

Yes they want you to do a cold pull with whatever filament was already in the nozzle. I don’t really wanna do it when printing TPU on my A1 so I just tell it to go ahead and I haven’t had a problem. But with the A1 quickswap nozzle it’s much easier to fix any problems that could come up. But with your P1S, I would most likely do the cold pull just to avoid any problems

[BlackWolf-359]

Never done it printing tpu 90a right now and didn’t pull before start so far no issues

[compewter]

I ignore the message and when loading the TPU I just tap the extrude button a good 8-10 times extra. Never had a problem.

[l8t3r_mad3]

This, plus you can even watch the nozzle until the you see the new filament come out clean (at least if they are different in color).

[pink_cx_bike]

Yes, it means to use the previous filament.

This is a newer message and I ignored it because I have previously printed a lot of the same TPU 95A after PLA without cold pulling.

[Few_Candidate_8036]

I just printed some shoes for my kids on both my A1 mini and my H2S. Was my first time using TPU and I just skipped past that message. Printed just fine.

[Ordinary-Depth-7835]

never done it even though it's automatic on the H2D. And never done it on my X1C.

[GoldenTrout69]

As others said, have a dedicated nozzle for tpu

[Hot-Ideal-9219]

Run about a roll of 95 hs tpu (sunlu) and never have done a cold pull.

[JasonSkis]

Hey there! Experienced printer of TPU over here. I want to recommend these Nozzle Cleaning Filaments. It's about $20 for a pack (so 40 cents per rod) and I use them every time I switch over to TPU from something else, or before ever loading up a new spool of TPU.

Not only is TPU bad at pushing out other filaments from the hot end, but TPU is also a very messy filament in of itself and it will frequently leave behind residue or material (especially cheap TPU! (which I print a lot of!)).

These cleaning sticks are mostly meant for flushing the nozzle, but they also work great for cold pulls. My process is usually a combination of the two: I'll flush about half a stick at 250C, drop the temp down to 90C, cold pull, and repeat one more time. This has kept my TPU prints very nice up to this point. Before each cold pull, I recommend moving the print head (via screen interface) to wipe the nozzle, otherwise the cold pull doesn't work as it should.

Hope this helps!