Original Prusa MK3S

The Prusa MK3 is by far the best 3D printer I have worked with and now they have released the MK3S.  I got to really appreciate my MK3 while waiting for the Multiple-Materials-Unit 2.0 (MMU 2.0) to arrive.  The MMU  is a story on it’s own but it is also very much part of this one.

MK3 In Review

The MK3 print quality is superior to what I get out of any of my other printers.  Since I upgraded to the R3 extruder with the angled fan I’ve been blown away.  Prusa is setting the standards and has a bright future ahead.

MK3 Issues

That isn’t to say the MK3 was perfect.  The biggest issue I had with it was the filament sensor didn’t work on many of my filaments.  I turned it off a because it just caused problems.

The only other complaint I had is that you have to disassemble the E Axis to clear an hot-end clog. Clogs are rare so this is a minor issue but really shouldn’t require major surgery to clear.

MMU 2.0

I see the potential but it has offered me nothing but pain.  Working with it has taught me a lot about 3D-Printing failures.

Where the MMU shines is having filaments already loaded.  It is really nice to just select a filament in the slicer.  The majority of the time the filament loads without issue and this is a real time saver.

MMU 2.0 – Issues

I’ve already covered the real issue with the statement above,  “The majority f the time the filament loads without issue…”  The problem is when it doesn’t detect that it has not loaded a filament properly and prints anyway there is a gap in the layers where it didn’t have filament.  Needless to say, the print is destroyed in that single act.

MK3S / MMUS 2.0

With the release of MK3S the design of the MMU 2.0 design did not change at all.  The MMUS 2.0 kit is the MK3S kit and a ‘filament buffer’.


What is the ‘S’?   Simply put, it is the new R4 extruder parts.  This is a complete redesign of the extruder and x-carriage.  For MMU 2.0 owners the upgrade is free when they act on the email to go through the ordering process.

  • Filament sensor: Completely replaced with a mechanical/optical solution that detects when the filament door moves.
  • Serviceability.  The R4 extruder does not require a complete tear-down to clear a clog.  I would recommend MK3 owners order the kit to have it on-hand for the next clog even if you don’t care about the filament sensor upgrade.

The kit is a new filament sensor module, a couple of permanent magnets, a steel ball and some nuts and bolts.

MMUS 2.0

The MMU itself has remain unchanged so the MMUS upgrade is:

  • MK3S Upgrade
  • Filament buffer

The filament buffer may be a manufactured part because I couldn’t find in in the ‘printable parts’.  It will be a month or so before I see mine and can report for certain.


The MK3S is out and being shipped.  Upgrades are in the works and MMU 2.0 owners get the upgrade for free. Be sure to act on the email they send.

The testing for the MMUS had 92% success over 600,000 filament changes.  The other 8% completed but required user intervention.  That is a lot better than I have experienced.  I am really looking forward to seeing what they have come up with in action.

The only serious issues I’ve identified on the MK3 has been filament detection.  The filament detection issues was amplified 100 fold by the MMU 2.0.  Sensing when the extruder door moves is a great solution.

The other serious issue on the MMU has to do with the filament from retractions. The current solution, coiling, is comical until you watch it snap the filament a couple of times.  The ‘S’ upgrades should make the MMU a lot more reliable as well as making the extruder serviceable.  Sounds like a fantastic update!


Author: Marc

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