Prusa MK4 Filament Guide for PTFE Fitting

Useful for feeding filament from dry-box or dryer.  

Remixed from the original mk3 design.  Increased height between printer frame and forward angle to eliminate collision with the MK4 extruder carriage, and revised the “clamp” to be tighter using the Prusa filament guide as reference.

This fixture can be used with a PC4-M10 fitting that allows the PTFE to “pass-through”, or one that blocks it.  I recommend a pass-through fitting, with a few millimeters of PTFE below the fixture, as this ensures the filament only contacts the tube and not the fixture.

* Updated 2-MAR-2024:   Added “Tall” version, which is 40mm taller than the original.  For very tall prints where the print head gets near its full height (Z=221), the original design only leaves about 25mm clearance which can result in a sharp bend of the filament when the print head is far left or far right.  This new version, if you have the additional 40mm vertical space for it, minimizes that issue.  

* Updated 18-SEP-2024:   Added a “Tall-Secure” version.  This baby “ain't going nowhere.” Rather than a “snap-on” mount, this version uses a two-part clamp with (2) M3x10 or M3x12 socket head screws and (2) M3 nuts.  Most people find the snap-on mount satisfactory, but this two-part clamp eliminates any possibility of the Guide getting pulled or knocked off of the frame.  It might survive a nuclear blast.  For this version, print both the Prusa MK4 Filament Guide Tall-Secure_Main.stl and the Prusa MK4 Filament Guide Tall-Secure_Clamp.stl, then refer to the Prusa MK4 Filament Guide Tall_Secure - Instructions.pdf for assembly tips.

* Updated 20-JAN-24:  Revised the “Tall-Secure” version to be less bulky.  This results in a few more millimeter overhead clearance and a ~20% reduction in filament.  The new versions are labeled as “V2”, the the older versions have been moved to a “V1” folder.

Should the PTFE pass through the guide, or not?
By default, this fixture allows 4mm PTFE to pass through, unless your fitting blocks the tube.

I recommend letting it pass through, protruding a few millimeters below the fixture. This ensures that when filament exits at an angle to the left or right, filament contact is with the PTFE rather than the fixture. For this option, you need a pneumatic fitting whose internal diameter is greater than your PTFE tube (i.e., a fitting with a ~4.6mm ID for 4mm tube).

If all you have is a fitting that blocks the PTFE, it will still work.  The design of the fixture should prevent it from dragging on the metal fitting.  The fixture itself will guide the filament.

If you have a pass-through fitting, and for some reason do NOT want the tube to pass through, you can print and add the “PTFE Restrictor…” before screwing in the fitting.  Note there are two different designs for the original designs (v1) and the newer design (v2), so print the appropriate one.