Cannot load BL HF TPU in P1S a second time - Help!

Bambu Lab P Series Troubleshooting
1

Frustration level is sitting at defcon 9 here folks.

-TPU is new and freshly dried in a Creality dryer/dry box.
-Feeds directly into coupler out of dry box with no resistance or bends.
-TPU successfully loaded once, and printed until it seemed to clog on first layer of a basic print.
-Removed filament and printed a PLA test print directly after. Everything working normally.

  • Hotend has been removed and extruder disassembled, all working as it should. No debris inside and extruder gears not clogged or dirty.

Now when I try to load the TPU (both with the “load” process as well as manually heating and feeding) it refuses to load. If I hold slight pressure against the filament the very first time it tries to feed, I can feel it pull a few MM of filament in, then it simply will not pull any further. It will not do anything after it pulls the first few mm. I can pull it back out with minimal resistance. I can repeat the feed process a dozen times and it will only pull a few mm, then it gives up.

As I feed the filament in there is slight resistance before it hits the very end, and I am assuming what I feel is it passing through the filament sensor arm. When it bottoms out I am assuming that it is hitting the extruder gears due to it pulling a few mm.

What am I missing here? TIA

2

Have you taken apart the extruder to have a look at what might be going on inside?

3

Yep, all looks as it should.

4

Did you try adjusting the extruder tensioner screw?

Extruder Maintenance Guide: Cleaning and Lubrication - P1 series | Bambu Lab Wiki

5

I have not as there seems to be mixed opinions on whether or not you should. Research indicates this was designed to be fully tightened, but please correct me if I’m wrong.

6

Bet it’s still wet.
Sounds like it’s still wet.

Betcha. 25 char yet?

7

Wiki says: Don’t forget to carefully tighten the four extruder screws and the idler tensioner screw to prepare it for installing it on the printer.

I cannot find anything that says the tension screw should be any less than fully tight.

After extruder disassembly to clear a clog, I tightened mine fully. I’ve printed a lot of 95A TPU, PLA, PETG, and ASA since then with no problems.

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8

If you have it fully tightened we must look for another reason.

9

It is fully tightened, I am completely baffled. If it didn’t load the very first time I think I would be LESS confused… What changed between then and now?

Anyone else notice slight resistance ~5-10mm before fully inserted? Just making sure this is normal operation.

10

#1 - It has undergone over 10 hours of blast drying at this point so I am highly doubtful.

#2 “Betcha. 25 char yet?” - What does this mean?

11

You may be correct, but let me share a little story.

I ordered Siraya Tech 95A HF because at the time BL was out of stock. In resin circles Siraya has a good name so I thought, why not. I needed it quickly and couldn’t wait so pulled the trigger.

Loaded up in my S4 and let it dry for about 6 hours. Then started a print. Flow was horrible, and thought I somehow had a clog. Nope (saving time, did all the normal troubleshooting).

I was using a HF Obxidian nozzle so I swapped for the standard Obxidian. Using BL HF settings because I can’t print it to do any calibrations. Nope, now almost no extrusion.

Switched to another brand TPU and it printed a little test print without issue. It was orange instead of black so…ok let’s go back to the Siraya Tech now and see what happens. By this time I’ve already contacted them to see if I was doing something wrong. Their suggestion was to dry it. Seriously?

Hey I dried it for 6 hours already, I mean it was a new spool and right out of it’s wrapping.

To wrap up, after going back and forth, scratching my chin (helps you think), and making up new cuss words I decided to take their advice and dry it overnight and into the next day. A total of 15 hours, not counting the original 6.

Printed. Like. A dream. No under extrusion, no tatty looking lines, just pure TPU with each pass. Through the whole spool.

Now you may have it dry and it be something else. I mean, I’m wrong far more than right. TPU likes water. Not as much as ASA or ABS, and certainly not as much as Nylon. When all else fails, look to the obvious, and trust the manufacturer. Well, that was my lesson at least.

the 25 char, well when you reply you have to use 25 characters before it will allow you to post. I’d say I was being funny with that but if I have to explain it, it wasn’t funny.

12

I appreciate your effort, but can you explain to me how not-quite-dry filament will cause it to not pass through the extruder gears and enter the hotend?

13

Glad you appreciate my effort in trying to help you. Your tone leaves me uninterested now.

Good luck.

14

TPU tends to need very specific requirements otherwise a handful of variables will ruin your experience.

  • I’ve suffered something along the lines of what you’ve encountered before. My investigations led to the [Tension Gear] that places pressure against the [extruding] wheel to be “too tight”
  • The design is very limiting as to the amount of ‘tension’ you can reduce/increase when it comes to different filaments. Bambu Labs design on the X1/P1’s is pretty much a master set adjustment (if you loosen the screw that pushes the spring too much the toolhead cover will NOT fit) You’ll notice a screw on the [RH] side that sits flush on the [extruder unit] when the cover is off.

Normally you’d want to [reduce] the tension against [TPU] because of how elastic and soft it is. If the gear teeth bite to far into the filament you’ll encounter extrusion issues with layers and tolerances. Retraction is also a major factor because it doesn’t like to be fed outwards/inwards in such fast movements while being within the hot zone.

So limit retraction to 0.5-0.8mm

  • retract speed - 25/30mm/s
  • temp - 220/230 (This will vary but is important to prevent stringing)
15

Thank you for the very informative response! I will reduce tension and report back.

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16

Ah yes, you cannot explain a connection between filament moisture content and the issue I am having so you use my (professional) “tone” as an out.

Good day.

17

You’re welcome, as I stated there’s only a very small room for adjustment.
I forgot to mention the method of which I was able to achieve a decent range of adjustable tension and that was utilizing a [short screw] . I did this over a year ago and have forgot the exact dimensions of the metric sized screw but in theory if you shorten the screw - you’ll reduce tension against the spring *Wallah lol

I cannot guarantee this will work for you but I can say it worked for me when printing TPU on an X1C. Another factor will be the shore hardness of the TPU used, in my case I was using 95A. I’ve since switched to using a flex PLA 98A with zero issues as well

18

No, I am more than willing to help anyone with whatever.

I have spent a week going through exactly what you have described, and explained what the solution was. You then have a choice to either accept it and attempt to use it, ,or disregard.

Your tone isn’t anywhere near professional. It’s condecending and curt. I can accept your willingness to disregard what I’ve experienced myself with this problem. I can also readily admit to being wrong when I am. I don’t take kindly to folks that seem to believe that they know better when they’re the ones asking for help.

THAT is why I choose to limit any “explanation” to you. Quite simply I don’t feel it would do any good, I don’t want to, and I just don’t care for you. Personal choice I suppose.

I wish you well. Good day.

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19

This worked immediately, I just backed the screw out until it barely slid in beside the housing. 100 karma points to @ProtoSpyre !

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21

I’m extremely happy this solved your issue @thorp-e !
Anyone who started with the infamous [Enders] and swapped to direct drive extruders went through this experience especially with swapping from hard/medium/soft filaments.

When first seeing Bambu Lab’s extruder unit I questioned how were supposed to adjust tension?. To help their reasoning it’s more so related to having the required force to pull filament from the AMS and the Buffer helps relieve some of that but not all.

Anyways, Happy Printing! :grinning:

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