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RMU MK3: Innovative filament buffer by the Wedge Group

What is it

Compatibility: The RMU MK3 is designed for the MMU2S. It is not compatible with the MMU3 due to MMU3's different mechanical design.

The filament buffer included with the MMU can introduce a lot of friction to an already sensitive system, and takes up a considerable amount of space. The RMU MK3 is a slim, sleek unit that attaches to the side of the printer and provides the same functions with considerably less friction.

The RMU MK3 filament buffer mounted to the side of a Prusa i3 MK3

From their site:

  • The RMU is a Tower Buffer. It stores filament in the body section of the tower when not in use
  • A compact storage for material not in use, the 5 channel RMU fits to the rear of the Prusa I3 Mk2 & Mk3 and Bear Frame.
  • Form meets function, the beautiful minimalist design looks perfect and does not impede the printer in any way.
  • No messy tangles of filament as it winds back between material changes.
  • Almost frictionless feeding of material. Does not strain to the feeder mechanism.
  • Simple, reliable loading of material into the buffer. You can even do it on the fly.
  • The RMU expands the footprint of the Mk3 by just 40mm on the left side of the printer.
  • Short travel distance between RMU and MMU.
  • Utilises existing Prusa mount points
  • Safe parking of material at jobs end
  • Easy side load of filament
  • Opening the buffer still keeps all the material constrained – no messy loops of material
  • Super easy access to load and unload filament.

Building and Operating

Building

The RMU MK3 requires a set of printed parts, which are available directly from the Wedge Group or from community members. The assembly instructions PDF is the definitive reference for the build and should be consulted throughout the process.

RMU MK3 buffer wheels and internals with the unit open

The RMU MK3 latch mechanism

Full build video and review below:

Loading and unloading filament

Please take some time to review the video below on how to load filament into the buffer:

Filament being loaded into the RMU MK3

Unloading requires different steps:

  1. From the printer menu → "Eject from MMU" and select the channel.

  2. Cut the end of the filament at an angle. This will make sure that the filament is the same width as the rest and won't get stuck.

    Correct filament tip shape for the RMU MK3

  3. Open the RMU and start pulling the filament away from the MMU.

  4. Once the filament tip is close to the RMU, start winding the excess back onto the spool, taking great care to not tangle the filament on the spool.
  5. Continue to do this until the filament has cleared the RMU and make sure to properly store the spool with the filament end tight.

Troubleshooting

See the dedicated RMU MK3 Troubleshooting page.