Prusa MK3S+ Filament Feed Tube Mounts

Updated 2023-04-10

Remixed models to add push-release fittings to the fs_cover and Z-axis top.

I love my Prusa, but over the past year or two, I have been frustrated badly with filament jams. All of you experience this if you use the standard feed system, and know my frustrations.

One day, after a printing a large job with a ton of head movement, I decided there was no amount of guiding or spool design that could reliably deal with the issue. (yes I know spring loaded spools can help as can a buffers. I want cheap and simple) The root problem is filament is stiff. When the head moves away from the spool, filament is fed out. When the head moves back, the spool cannot retract, so the filament is pushed back over the spool. When the head moves back again, this slop causes the filament to cross over itself on top of the spool, and then jam. Over and over and over.

That's when I realized how awesome Bodentubes were (not the feed system. Just the tube). Because the ends of the tube are mounted on both the head and frame, the length of the tube never changes, it just flexes out. Same for the filament inside. Therefore, filament is not drawn out by head movements. I then racked my brain trying to find the best place to mount the fittings on the frame. I tried many many solutions from others, but they were too bulky or made filament feeding difficult. That's when I came upon this solution. Its two simple part swaps that have no effect on the printer. Honestly, it would be nice if Prusa would just ship the i3 MK3S+ this way. It makes the printer far more reliable. Since I swapped these in, I have only had one jam. and that was from a bad loading on my part.

The Z-axis cap comes from Prusa, but so far cannot find the source for the fs_cover. I thought it came from Prusa and the MMU, but the models do not match. I do know it was remixed originally from Prusa obviously, but it bothers me that I cannot be sure. If you recognize it, please let me know so I can add attribution. Both 

I have been using this solution for the past 5 months now, and have decided to share it. For this first release, I have added a small funnel to the back of the Z-axis mount that makes it super easy to load filament without having to feel your way around or wiggle it in.

Enjoy your jam free printing!

A couple other thing of note. 

1. When you swap filaments, make sure you first pop the tube out of the fitting on the extruder first. The filament will have a bulge at the end that will not feed into the tube (unless you get a tube with a wider internal diameter). Snip this off before trying to respool your filament
2. When you run out of filament, and trigger the run-out sensor, its a good idea to unscrew the fitting on the top of the extruder before ejecting the remainder. I find that randomly, the filament can curl a bit, and get caught on some of the internal geometry. Plus, you need to remove your tube anyways to get the small chuck of filament out anyways. Better to remote the fitting and be safe.

Parts Needed:

• 2x PC4 M10 push release fittings
• 1x 24" PTFE Bowden Tubing (1.9mm ID / 4mm OD)

1. Attach the fittings to the extruder cover and Z-Axis cap. I recommend using a small tapered tool to round out the opening in the back of the Z-Axis cap. Printing can leave it slightly oval. a small drill bit also works well.
2. Install the parts on your printer.
3. Press the 24" ptfe feed tube into the fittings. Make sure to push the tube until it stops
4. Slide your Original Prusa Filament spool holder (or compatible model) to as far left as possible on the top rail of the printer. You should find it aligns very well with the mount point on the Z-Axis cap.
5. Mount your filament on the spool with the filament feeding under, rather than over.
6. Slide your filament into the back of the mount point, and it should be guided into the feed tube, and down to your extruder.

Jeez. I didn't start this intending to write book. I guess there was more to this than I thought.