Sunlu S4 dryer, P1S, Sunlu TPU - not feeding from dryer

Bambu Lab P1 Series Troubleshooting
1

OK, this might be very specific and I don’t know (yet) how to troubleshoot this. I got my Sunlu S4 dryer on Sunday, and dried a roll of Sunlu TPU all day. That’s the only thing in the dryer right now.

I have the “Smoothy” Y splitter on the printer, and that’s been working fine with my AMS or with a roll of PLA on the rear spool holder (after manually loading it when I want to print from that).

Now I tried to feed the TPU directly out of the dryer into the Y splitter. Anyway, I load the TPU and it gets to the extruder OK. BUT, the extruder really isn’t pulling the filament at all. I tried a few different lengths of PTFE tubing, probably not optimal yet. So that was discouraging. I opened the dryer box to observe the spool, and it doesn’t roll. Manually spinning the spool, there is a lot of resistance.

Next experiment was placing that same Sunlu TPU spool on the rear spool holder and feeding it through a short PTFE tube into the Y splitter. No problem there: once loaded, printing was fine and it fed as expected. But of course, I don’t want my TPU hanging in the breeze after going to the trouble of drying it, and AMS is not an option unless I get the BBL TPU. And the dryer box is supposed to let me do this. Documentation is - cough - almost non-existent for the dryer.

Anyone successfully feed a P1S (or other printer) right from this dryer box? I will try again with a different spool from a different vendor to see if make any progress.

2

Yes, people feed filament directly from drybox all the time. Most dryboxes were designed that the spool can roll smoothly, unless bearing seizes or so.

My particular case is different than others. I have hard modded sunlu s1 to have a quickfit connector there to act like a stoppage to keep ptfe tube from sliding in and out.

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You should also check the resistance of the ptfe path from drybox to the toolhead. Remove the ptfe tube from toolhead then manually push the filament through the ptfe tube from the drybox. If you find resistance anywhere on the ptfe path, then you’d know where to fix

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3

OK, I think I found the problem. The bearings on one of the rollers were kind of stiff, which probably kept the spool from rolling enough. I moved the TPU spool to a different position in the S4 and that worked OK. And the rollers snap in and out, so I moved the stiff roller to a position I don’t care about just now. I will likely contact Sunlu to get a replacement roller. And I will play around with the PTFE tubes to see what works best, but for now, I can move on.

Probably a stiffer filament would not have shown the same problem.

Thanks