Filament buffer sticky

Bambu Lab AMS
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After going through a roll of PAHT-CF (ESUN), i noticed that the filament was getting stuck during retraction into the AMS. I traced it to the Filament buffer on the back of the printer. If I manually move it back and forth, and then the AMS can retract the roll. It appears the spring is a little weak. It could be that the issue is not the Buffer but the PTFE tubes between the buffer and the tool head…
I noticed that the CF filaments in general, build up quite a bit of friction in the PTFE tubes. I like to use the AMS, rather than the External holder, mainly because the AMS keeps the humidity in check.
Anybody any ideas or suggestions…?

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Have you tried adding weight to the CF spool? That worked to fix the retraction issues for me.

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Jon, thanks for the advice … where did you add the weight in the center of the roll? The esun rolls are plastic, and have a very thick solid cardboard center. The empty weight is probably 2x the weight of a regular plastic spool…

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5 Likes
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The problem is when the filament goes through the feeders, it gets knurled making it slightly bigger in diameter, enough to restrict it’s movement through the PTFE. This seems to happen more with blended filaments such as CF and glow. I fixed it by replacing all the PTFE with thin wall 3mm internal diameter (standard is 2.5mm). The only problem is that it’s more susceptible to kinking so care needs to be taken to ensure the bends are smooth. You could print radius curves to prevent this, I’m looking at putting 4mm springs on the outside of the PTFE on bends.
But the filament hub motor underneath is not very powerful and I’m sure someone will come up with a higher torque version.

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Thanks for all the advice… I will try the bigger tubes first… my spool is not slipping in the AMS, it really pulls the filament right, but the collective friction in all the tubes, and probable the “sanding” of the ptfe from the CF/GF rubbing against it…I’ll post back when I got the tubes installed

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If you can get Capricorn tubing in 3mm, then I’d recommend it just for the quality. I couldn’t find it where I am so just used cheap PTFE but will upgrade later. You need about 3m depending on where your AMS is located. Mine is on the right but I’m sure you could reduce the length of all the tubing by locating it on the left (as that’s where the tube enters the printer) and move the buffer remotely to near the AMS :thinking: