Notes on the MK4 and MMU3

My interpretation of the MK4 and MMU3

Last Update Sept 8, 2023

 I built an MK4 and plan to upgrade my MMU2 to MMU3 to use on the MK4.  Overall I like Prusa Research reliability with good support and a large community of users.   My MK4 prints well out of the box.  Saving a few dollars on cheaper systems may cost you thousands of dollars in time.  The 3D printing experience for me is vastly improved with the MK4 vs MK3 series printers.

First impressions of the MK4 Firmware 4.7.0-4.7.2 and 5.0 RC1

I am very happy with the MK4.  I carefully built it from a kit.  Everything checked out and initial setup worked well.  WiFi, PrusaLink, and ease of use have greatly improved with 4.7.x firmware.  It is about 20% faster overall and more speed coming with Firmware upgrades in the future.  My wife notes it is quieter than my MK3S+.   Many parts on the MK4 are stronger vs. the MK3s+ 

The MK4 is a big improvement that can put reliable 3d printing into more hands.   Load filament, keep sheets clean and run, run, run.  That is what I have been doing.  

There are still some minor problems with seeping of filament from the nozzle when not running and heating.  I have found extra purging at filament change may help.  To get all air bubbles out of the melt area. Hopefully software updates can  minimize this in the future. 

Significant Details

Mods I have done for the MK4

  1. Put a sock on it.  You must tell the printer it has a sock,  Enable the sock in Settings; Hardware, Nextruder Silicone Sock.
  2. Deflector for the Heat sink Fan   A good thing to have based on initial reports that state the hot-end fan may interfere with the cooling flow on the part.
  3. Squash Ball Feet x 6I have a remote power supply in the Prusa Enclosure.  I wanted the unit a little higher to help keep it off the power cables for the remote power supply.  Squash ball feet may also help reduce noise/vibration.
  4. PC4-M6 and PTFE tube anchored at the other end added.   See explanation and picture below.

This is significantly fewer mods than I did with the the MK3s+ to get it to my standards.  All minor, a big improvement.

MK4 vs MK3S+

What stayed the same on the MK4 vs. the MK3s+?   The frame assembly, Y and X axis rods, Y carriage, heat bed and the power supply.  The Full 4K upgrade offered by Prusa makes it a full upgrade.  All except the new lighter frame. Not a structural issue. 

You could buy a full MK4 kit and have 2 printers when done.  It could be a better value, depending on space available and your needs.  Be warned, you may not want to use the MK3 series anymore after using the MK4. 

If you are on a budget and want nearly 100% functional upgrade, I recommend the MK3.9. Gets everything but the finer servos.  Servos still can be added later if desired.  For most the upgrade would be great.  You print your own printable parts so don't tear the MK3x apart early if you do an upgrade.  

Some things Prusa told you about the MK4

Some nice things that may not be mentioned

Dimension differences of the MK4 vs MK3s+  From measuring the MK3s vs MK4 parts.

Notes on the MK3.9/4.0 upgrade: The v1 Mk3x to MK4 (full) assembly instructions show the frame assembly, power supply, Y and X axis rods, Y axis carriage and and heat bed are re-used when in good condition.  These parts do not change in the MK4  The Y axis thermistor is changed for the new Buddy board connection.  The instructions then links you into the MK4 build at the point the buddy board is installed.   I haven't seen the kit, but from this I assume the following about an MK3.9 and full MK4 upgrade.

MK4 V1 vs. V2/3 printed parts

Look  on, in the comments on the MK4 printable parts. A user compared parts and listed the ones that did not change and the ones that did change.   Those that did not change were still marked V2 instead of V1.  Most changes appear to be driven by the Prusa assembly group, to make assembling a printer easier and faster.

Some things I think should still improve, minor overall.  See Software rule #41

MMU3 with  MK4 integration testing Oct-Nov 2023 for me.

Changes to the MMU3 vs MMU2 

The changes to the MMU3 vs. MMU2 improve reliability,  filament flow, sensor function and software interface.   It seems to cover the majority of pain points I had with the original MMU2.  All the printed parts change.  The 2 mount feet for the MMU2 could be used on the MK3S+, but the MK3.9/4 will need the new mount feet.

  Buffer changes


My print of the name plate.

Improvements I would like to see

A better cooling nozzle that better covers the printed filament.  

Z anti-backlash screws. 


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