Overview:

I recently purchased a Sunlu S4 dryer that I also print out of.  Unfortunately, I have had issues with the dryer pulling the PTFE tube inside the unit and jamming the spool. 

I figured I could install PTFE couplers in the filament openings which would keep the PTFE tube secured. I had some larger PTFE couplers (M10) that would thread into the dryer’s plastic housing slightly, but only on the top holes.  However, I do not like printing out of the top openings because it becomes more of a pain while loading/switching filaments, and the holes on the sides are slightly larger and did not work with these couplers.  I also had some M6 couplers on hand, but their threaded section is not long enough to extend through the dryer with room for a nut.

I designed adapters to fit the openings that will accept an M6 heat set insert.  The PTFE coupler can thread into this insert.  A printed nut secures the adapter to the dryer.  This solution has worked very well.  I’ve included a version of the adapter for the top holes and the side holes.

In addition, I designed some plugs to be printed out of TPU that can seal the coupler when not in use. 

Here is a link to the heat set inserts I used (M6x8x8):

https://www.amazon.com/Yaocom-Inserts-Threaded-Printing-Components/dp/B0DNJNLP95

These M6 couplers are not identical to the ones I had on hand, but they should work (I don’t remember where mine came from):

https://www.amazon.com/UniTak3D-Pneumatic-Connector-Extruder-Printers/dp/B08QMRLPC5?th=1

I also have the Creality Space Pi X4 filament dryer, but I haven’t had any problems with that one yet. I’ve heard that others have, so this solution may work for that as well.

Printing:

I recommend printing the adapter in PETG at a minimum since they will be subjected to higher heat.  I also increased the perimeter count to 6 for added strength.  The coupler plug should be printed in TPU.  No supports required if printed in the orientation shown.