PTFE Pass-Through for Hinged Lid on Original Prusa Enclosure Using Magnetic Coupler and PC4-M6 Connector

This started as a simple project to add a PTFE pass-through near the back of the hinged lid on Prusa enclosure for connecting to an external dry box.  This has been tested and used with a Prusa MK4 printer, but based on measurements of my MK3S+ it should work for that as well.  The basic design replaces the top-rear cover with a pass-through oriented at a shallow angle close to the hinge axis to minimize PTFE tube movement as the lid is opened; the pass-through is also angled slightly in the Z-axis for the tube to clear the frame as the lid is opened.  It uses a PC4-M6 connector on the inside, and has a magnetic coupler on the outside.  Included is a model for a mating magnetic coupler with a PC4-M6 connector.  If you prefer to use a PC4-M10 connector on the outside, the magnet spacing on the external coupler is compatible with the “NoOffset” model found here: https://www.printables.com/model/32368-join-ptfe-tubes-together-magnetically/files.  The magnetic couplers use 5x5mm magnets (press-fit) such as these: https://www.amazon.com/gp/product/B07JNT512N

Reverse-Bowden Tube Management:

While the pass-through design was relatively easy, it took awhile to solve issues with dynamic movement of the PTFE tube while printing, and I finally have a complete solution that I believe is robust enough to publish.  While static positioning of the tube throughout the range of print head positions looked fine, tube movement during a print was more unpredictable due to fast X-axis moves, model specifics, and stiffness of the filament used; this occasionally resulted in the tube getting hooked on either the upper-left corner of the printer or on the end of the fire suppressor tube.

The solution was to add a tube guide that attaches to the upper-left rail of the enclosure and pushes the tube away from things that can snag it; there are two different designs, one to keep the tube away from only the printer (no fire suppressor installed) and the other to keep the tube away from both the printer and fire suppressor; only one of the guides is needed (choose the appropriate design).  A single M3 thermal press-fit threaded insert is used to attach the guide to the enclosure frame; it will accept up to 10mm long inserts, depending on the length of screws you have (6mm length was used on mine, and it is quite solid).  No supports are required, but note that the two guides have different orientations relative to the build plate (shown in the .3mf files).

Optional Clip:

Also included is a model for a clip that attaches near the front of the upper-left enclosure rail to hold the unused tube out of the way (the front tube from the internal spool holder when the rear tube is being used, or the rear tube from the pass-through when the front tube is being used).  You could do without the clip, but it keeps things tidy.  A single M3 thermal press-fit threaded insert is used to attach the clip to the enclosure frame; it will accept up to 6mm long inserts, depending on the length of screws you have.  No supports are required for the clip.

2025-06-05 Update: Corrected the link to the PC4-M10 “NoOffset” model.

Required Parts:

2x  PC4-M6 connectors

6x  5x5mm magnets

1x  PTFE tube 4mm O.D. x 2.5mm I.D., 67cm long

1x  M3x6mm (5mm O.D.) threaded insert (for tube guide)

1x  M3x6mm screw (for tube guide)

Optional Parts:

1x  M3x6mm (5mm O.D.) threaded insert (for tube clip)

1x  M3x6mm screw (for tube clip)

Printing Notes:

• Print using PETG at 0.15mm layer height, with 15% gyroid infill.
• No supports required for any of the parts.

Installation Instructions:

Pass-through Assembly:

1. Press three 5x5mm magnets into the pass-through until they are flush with the surface; make sure that all three magnets have the same polarity.
2. Temporarily attach three more magnets to the magnets already in the pass-through (this ensures proper polarity for the coupler and makes them easier to insert).  Line up the coupler with the magnets and press the two pieces together to partially insert the magnets, then separate the coupler from the pass-through and press the magnets fully into the coupler until they are flush with the surface.
3. Screw the two PC4-M6 connectors into the pass-through and coupler.  They should be snug so that there is no internal gap, but no need to go crazy over-tightening them.
4. Open the enclosure lid and remove the nylon rivet from the top rear cover plate by pushing the center post of the rivet from the inside.  Save the rivet for reassembly.
5. Remove the top rear cover plate.
6. Insert the pass-through into the hole from the outside, hooking the tab on the pass-through onto the front edge of the hole and rotating it into place.
7. Insert the nylon rivet to hold the pass-through in place.
8. Disconnect the existing PTFE tube from the extruder.  If using the PTFE clip, slide the unused front PTFE tube into the clip on the top left rail of the enclosure.
9. Attach one end of the 67cm PTFE tube to the PC4-M6 connector on the pass-through, and the other end to the extruder.

Tube Guide and Clip Assembly:

1. Add the thermal press-fit threaded inert(s) into the printed part(s).
2. Align the part(s) against the top left rail of the enclosure at the location(s) shown in the photos (tube guide mounts to the center hole on the rail, and the clip mounts to the hole closer to the front).  To assist with alignment, each part has a small post that fits into the hole on the top surface of the rail.
3. Insert the screw(s).

Miscellaneous Notes/Comments:

• Note the use of PTFE with an inside diameter of 2.5mm.  Unlike a bowden tube, a reverse-bowden tube has no need for the tighter tolerance of a 2mm inside diameter; in fact, it can be a disadvantage for longer tubes, transitioning to the connectors, etc.  Likewise, 3mm inside diameter does not work well either because it is too flexible and kinks easily.