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If you try these parts and this design, thank you! Please let me know if you have any feedback or issues.

N4 extruder parts are a modified version of the Prusa R4 parts for the Mk3S extruder.

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Revision History

April 1, 2019: Added a version of the X-Carriage (for both Mk3 and Mk3S sensors) for folks who are using X-axis parts with 16T idlers (e.g., Vekoj's x-axis mods).

March 18, 2019: Added an "N4A-XT" version for both Mk3 and Mk3S sensors.

• This version restores the vertical height in the extruder heatsink air channel to what would be found on the official R3 parts prior to the release of the Mk3S/R4 parts.  See the associated uploaded image for a better view of this minor change.  It probably doesn't make that much of a difference, but these parts are what I will recommend, as they have been working well on my machine for 3 weeks of straight printing now.
• Note: The indirect sensor version of these parts will require printing both the N4A-XT_IndirectMk3FS_PLATE1__0-20mm.stl and the "N4A_IndirectMk3FS_PLATE2__0-15mm_V1.stl" plates.  See related print settings and instructions for the N4A indirect parts.

March 1, 2019: Updated V1 to V1a of N4A and N4A indirect extruder parts.

• Minor fix to repair a hole on the lower extruder cover (heatsink cover) that somehow rebuilt to be too large.  Only the cover has changed.  If V1 was printed, please re-print V1a of only the extruder cover.

February 28, 2019: Updated V1 of N4A and N4A indirect extruder parts.  If you have printed the original version of these parts, don't feel like you need to update to V1. Changes:

• Slight widening and deepening of the airflow channel around the heatsink.  This is more of a tweak or optimization than a full change; the initial version has been very acceptable for me so far.
• Small adjustments to square nut slots on the X-Carriage, for ease of assembly.  The original .STL file that was uploaded was directly created from the official Mk3S x-carriage, but one slot was too loose and the other (bottom-most slot) was too tight and needed to be widened with an exacto knife.
• Affected Parts: Extruder body, motor plate, extruder cover, x-carriage
• In addition, the orientation of the motor plate in the N4-Mk3S-plate.stl file was updated to the correct print orientation.

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The Mk3S has the same slightly incorrect filament path as the Mk3 parts.  This misalignment caused issues for myself and others.  See pictures and this Github link for more information.

Notes: There are multiple options to choose from, to personalize your extruder to your tastes.  Original Prusa parts will also need to be printed (for example, the top cover above the Mk3S style filament sensor).  If a part is 'missing' from the .stl plates posted here, then the original part should be printed and used.

*Assembly instructions are the same as the official assembly instructions for the Mk3S.

• For the N4A Indirect Filament Sensor Assembly, a good place to assemble and insert the filament sensor cartridge is prior to installing the extruder idler.  Instructions are provided in the pictures on this page.
• The long extruder motor screw may need to be loosened slighty to fit the filament sensor cartridge in place (it has very tight tolerances).  If you loosen the extruder motor screw, be sure to tighten it again after inserting the filament sensor cartridge.

*If you are upgrading from a Mk3 extruder, there is now less distance between the bondtech gears and the top of the hotend heatsink.  This is a good thing, but you will need to trim your extruder PTFE tube to fit. Official dimensions are published here.

• Set the extruder heatsink (with PTFE tube still installed) in the extruder body.
• Use a sharp utility knife to trim where the tube exits the printed part filament path above the heatsink.
• IMPORTANT: remove the PTFE tube, deburr the fresh cut, and clean the interior thoroughly.  Any small bits of PTFE left in the tube will fall down into and clog your extruder nozzle if the tube is not cleaned.
• Re-insert the PTFE tube.

Original parts are published here.

N4 Parts

• These parts are directly created from Prusa's official part files released on their GitHub.  Only the filament path has been adjusted.
• There is an additional option of choosing a extruder cover with or without the venturi airflow port.  If you wish, you can experiment, and find if you can observe any differences between the two configurations!
• Note also that the compatible MMU2S extruder parts are also published here.

N4A Parts (N4 "Airflow" parts)

• I implemented some features that may help focus airflow from the extruder fan across and through the E3D heatsink.  Design intent is described further in the attached pictures.
• This set of parts is also compatible with the MMU2S system.

N4A Indirect Filament Sensor Parts (Edit - March 10, 2019: Moving these out of Beta.  They work great.)

• This set of parts fits the Mk3 filament sensor into the top of the extruder, making a hybrid with the Mk3S extruder body and keeping the Mk3 filament sensor.
• The original idea and implementation for this was published by martin_au and updated for the Mk3S on Thingiverse.
• USE THE MK3 FIRMWARE FOR THIS CONFIGURATION.
• This is not intended to be used with the MMU2S at this time.
• See parts list below for items that are necessary to purchase.

Purchased Parts list for N4A Indirect Filament Sensor Extruder (Note - these are Amazon Affiliate links. A small percentage of any purchase made through these links goes to help support my modeling efforts at no additional cost to you.):

• 1x MF63zz Bearing (Flanged, 3x6x2.5)
• 1x M3x6 screw (set screw recommended, standard socket head or button head is acceptable.  Do not use a countersink/flathead screw)
• Other assorted M3 screws, if upgrading from Mk3. (Hotend fan screws are a new dimension, etc).  Minimum count that I recall is I used 3 qty M3x14 screws, and 4 qty M3x20 screws, and these may not have been provided in with the original Mk3S kit.
• Short length of PTFE tubing (can reuse Mk3 R2/R3 filament sensor tube)
• Techflex F6 Woven Wrap, 1/2" Diameter (12.5mm), 490mm. Optional, but recommended upgrade for older version of Mk3: Woven Textile Wire Wrap, Minimum 470mm to 490mm length.

Testing Status for Indirect Mk3 Sensor Configuration

• First Print: Passed
• Filament Autoload: Passed
• Filament Runout/Jam Detection: Passed
• Filament Sensor False Positives: 0 false positives, after 300 hours of printing (note, color or material really doesn't matter any more with the intermediate indirect bearing)
  • Green filament: Passed
  • Transparent Filament: Passed
  • Shiny filament: Passed
  • Shiny black filament: Passed
  • Flexible filament: Passed
• PLA Jam Test (PLA, inside enclosure with doors closed, 50°C bed, 215°C hotend, normal speed, 0.05mm layer height, jam-prone filament): Passed, with two slow layers with very minor extruder skips.  Note: general best practice if your printer is in an enclosure is to print PLA with the enclosure doors open.
• Flexible filament performance test (high speed with retracts, without jam or filament leaving filament path inside extruder): Passed