Prusa Core One Nextruder Cover with Magnetic Latch

Unlike the MK4S, the left-side cover on the Core One Nextruder is attached by a screw, which makes it more difficult to swap the entire Nextruder heater/nozzle rather than just the nozzle.  This modified cover consists of 2 pieces, a base that attaches (with a screw) in place of the old cover, and a new cover that magnetically attaches to the base.  There is also a lever on the cover that disengages the magnet so that the cover can be easily lifted off.

Since the original model from Prusa was only available in STL format, I decided to create this cover from scratch.  The dimensions, location, and relative spacing of the bottom tab on the cover and the screw hole and mounting surface of the base are precise, and identical to the original model; the rest of the cover envelope and shape are extremely close to the original, but not exact since they are not critical to the design.

Tolerances are intentionally tight to ensure that the cover securely attaches to the base without rattling.  This necessitates thin walls and small gaps in the area of the lever shaft.  The model in the photographs was printed at 0.2mm layer height, but I was not able to achieve consistent quality at that setting.  Consistent, very good results were achieved by using 0.15mm layer height, and structural print settings.  I also found that using 3 perimeters rather than 2 resulted in much cleaner features for the lever shaft.

2025-07-11 Update: Added a version of the cover with a larger gap around the lever shaft to address problems with the lever getting stuck when printed using the original file.  I have printed several copies using the original file without any issues, but depending on filament type, printer settings, and environment, a larger gap may be necessary to ensure that the lever moves smoothly.  Also added a printing note regarding sequential printing.

Design Features:

• No supports required
• Lever to disengage the magnetic latch
• Uses the same bottom attachment tab as the original cover.
• Top edge of the cover self-centers on the screw head used to attach the base.
• Indentations on the lever and finger tab make it easy to hold the cover while removing or installing it.
• Magnets can be easily removed by using a 2.5mm hex wrench to push them out.

Parts Required:

• 2 x 5x5mm Round Magnets.  I used these magnets from Amazon: 5x5mm Refrigerator Magnets
• 1 x M3x10mm Socket Head Cap Screw (reused from the original cover)

Printing Notes:

• Print using a 0.4mm nozzle, 0.15mm layer height, structural, 15% infill.
• 3 perimeters is recommended.  It produced much cleaner features around the lever shaft than 2 perimeters.
• Supports are not required for any of the parts.
• PC-CF filament is recommended to match the other pieces of the Nextruder assembly.
• If you print both the cover and base at the same time, it is recommended to turn on sequential printing (as was done in the included .3mf files) to reduce the possibility of stringing between parts that may interfere with the lever movement.
• Please DO NOT use the .bgcode file that has been provided (always slice your own files for your specific printer, filament, environment, etc.).  The file were only included to provide a reference for approximate print time.

Assembly Instructions (refer to photos):

Step 1:  Insert the magnets.  Press 1 magnet into the base piece and 1 magnet into the lever part of the cover.  Ensure that the magnets are flush with the surface, and are oriented such that the 2 magnets will attract one another.  If you need to reverse one of the magnets, it can be pushed out from the opposite side using a 2.5mm hex wrench.  The easiest way to insert the magnets is to attach a magnet to a flat surface on the printer frame, line up the magnet hole on the printed piece, and press the piece against the printer frame until the magnet is flush; pliers can also be used.

Step 2:  Remove the old cover.  Remove the M3x10mm screw holding the cover in place, then pull the cover out and lift the bottom tab out of the Nextruder assembly.  Save the screw for the next step.

Step 3:  Attach the base piece to the back cover of the Nextruder assembly using the same M3x10mm screw and screw hole that were used for the original cover.

Step 4:  Grasp the new cover by the lever and finger tab, then insert the bottom tab into the Nextruder assembly as would normally be done with the original cover.

Step 5:  Rotate the cover into place.  It will seat flush against the base piece, and the center of the lever shaft will self-center on the screw head that holds the base piece in place.

Step 6:  Push the lever down to engage the magnet.