Threaded PTFE Bowden Tube Cap and Coupler

I didn't like any of the caps I saw for DIY dry boxes, so I made my own cap and coupler. 

Two main features:

1. Use tapered threads to hold onto the filament, so it never falls back into the dry box (similar to how wire nuts hold onto wire). 
2. Use O-rings to provide an airtight seal around the PTFE tube. 

Print Info 

• Printed on Creality K1C with Creality White Hyper PLA.
• Sliced in OrcaSlicer with 0.12mm Fine Creality K1C preset.
  • 15% cubic infill
  • 4 wall loops. 
  • 5 top shell layers 
  • 5 bottom shell layers 
• 28m print time and 4g filament.

Model

I included the Onshape project so you can tweak it to your liking.

O-rings

• The O-rings I had on hand were 2mm in diameter, so that's what the model uses. 
• I think 3.5mm ID x 7.5mm OD x 2mm thick O-rings should work. But I never tested this.
• What I ended up doing was cutting and fitting my own O-rings. 
• There's no need to glue the O-ring if you go this route. It's tedious and didn't work well for me. 
• Simply butting the O-ring material up against itself will provide an airtight seal. I tested it in a bowl of water by squeezing my dry box and didn't get any bubbles. 
• If you cut the O-ring to size, put it in, and it has a squashed, twisted, kinked, or rippled appearance. It's too long. It should look smooth when installed.

Tapered thread 

• The tapered thread can probably be fined tuned.
• I originally based the threads off of a 100% plastic (nylon?) wirenut that bit right into the filament and held very tightly. It worked really well. 
• But I was never able to get my 3D printed PLA threads to bite into the filament as well as the wire nut. I tried a few iterations, but in the end, I just made the threads larger and more spaced out, like a corkscrew. They work well enough in my opinion.