The Thunderdome MK2: Dual Bowden Merger Feed-Through for the Prusa Enclosure (FreeCAD)

What This Does

This part can be mounted on the top of the Prusa Enclosure. Two PTFE tubes go in, one goes out. The idea is quite simple: If you have two dryers from which you want to print, you only have to retract one filament through this part and can then push your other filament through, right to the extruder.

Parts

1x all three printed parts

4x M3x12 countersunk screw

2x M3x8 countersunk screw

6x M3 hexnut

3x PC4-M6 tube connectors

PTFE tube, about 2 meters for two dryers

Optional Preparation of the Printed Parts (untested)

When I print with this thing in place, I sometimes get a bit of noise from the filament being pulled through the channel in the merger block. I don't really care too much, but if things like that trouble you, you might want to smoothe the canal out with some fine-grained, wet sandpaper. I haven't done this myself, so I don't know for sure if that helps - but I would be surprised if it didn't.

Assembly

First you push 4 of the hexnuts into the bottom part of the “monolith” and attach the top part using the 4 M3x12 screws. Screw 2 PC4-M6 connectors into the threaded holes on top of the monolith. Tolerances are a bit tight, so best use a wrench or plyers. Screw the third PC4-M6 into the inner plate's threaded hole - this one needs to go in quite deep, or your filament might get cought in any gap left inside the part when loading.

Now remove the top center plug of your enclosure. Push two hexnuts into the recesses of the inner plate. Put the monolith onto the center hole of the enclosure, align the inner plate properly from the inside and put everything together with the two remaining M3x8 screws.

Now connect your PTFE tubing and you're done.

Printing Hints

I really suggest you use PETG for this print as PLA might have issues with heat when it gets warm in the enclosure. I used Prusament PETG Galaxy Black, and it looks really good.

I printed the parts with a 0,4mm nozzle and 0,15mm layer height. I would not suggest using much higher layers - the M6 printed threads are finnicky enough with good detail.

Version History

• 2023-10-31: Complete redesign in FreeCAD. Made the thing less wide so that the filament path is straighter. Works like a charm and the creaking noises are gone. Chnaged the name to “Thunderdome” because two go in and one goes out.
• 2023-10-27: First version. I actually used that, but it made creaking noises when pulling the filament.

Begging for Compliments

If you print this, please upload a make. It always makes me happy when I see that someone liked the stuff I made. :)

Sneak Peek into the Future

I am currently working on the Thunderdome MK3 - it will be really great and optimized for tubes with 3mm inner diameter. The friction in my prototype is dramatically lower than in the MK2 I'm currently using. And it will look very pretty…