The MMU3 is currently undergoing reliability testing. Once the stewards are confident in its ability to operate reliably, it will be opened for training and general use.

Approved Materials

Due to the loading and unloading process being very sensitive, the following materials ARE PROHIBITED:

  • Flexible Filament

  • Glow in the Dark Filament

  • Filled Filaments (wood, CF, metal, etc)

  • "B" grade filament from extrusion transitions

Additionally, the list of approved filaments is limited to:

  • ABS/ASA, PLA, and PETG from Hatchbox, Overture, Push Plastics, 3D Fuel, IC3D, Prusament, ColorFabb, Polymaker, Essentium, HSP Layer Line, and MatterHackers.

Exceptions may be approved with a steward's permission.


We use PrusaSlicer and the built-in profiles for this machine. The Prusa Knowledge Base has additional information on configuration settings and advanced use.

When printing with one material, select the MMU3 Single machine profile.

When printing with multiple materials, select the MMU3 machine profile.

Saving to SD Card

The SD card reader on the 3D printing computer doesn't work properly and may require you to save the file twice. Please keep this in mind when you use this machine.

Please save your files in a folder named after you. Orphaned files may be removed.

Feel free to add sub-folders to your folder as needed.


The MMU is prone to jamming with certain filaments. Many issues can be avoided by using good quality filament with minimal moisture content. Consider drying PLA/PETG for a few hours before printing to ensure jam-free operation.


The LCD menus are easy to navigate on this printer, and it does most of the work for you. Clicking the encoder wheel in will get you into the menu from the status screen, and rotating it will allow you to navigate the menus.

Loading/Ejecting Filament

Most of the time when using the MMU, you will be either using the Load filament menu option or the Eject filament menu option. Load to nozzle and Unload filament are often unnecessary, as the printer will load and unload filament to/from the nozzle when it needs to.

Loading Filament

To load filament, place the spool you would like to load onto the appropriate spool holder and remove the buffer cassette corresponding with the spool holder slot. Feed the filament through the cassette, wrap it around the roller, and then feed it into the cassette exit tube until it is near the MMU. Then select the Load filament option in the menu and then select the MMU slot you would like to load filament into. The MMU will then move the requested slot and ready for loading. Gently feed filament into the tube until you feel the MMU grab onto it, and then let go and wait for the MMU to finish the loading process. Use a light touch for this, it can be difficult to tell when the MMU has grabbed the filament otherwise. Then return the buffer cassette to its slot and repeat the process as necessary.

Ejecting Filament

Select the Eject filament option in the menus and then select the material you will be ejecting so the MMU can preheat. Once it is done preheating, the MMU will move the selector out of the way of the filament slot and push filament out of the front of the MMU. Cut the end of the filament off so it doesn't get stuck in the tube and then retract the filament by pulling on it from the spool end. Replace the spool when done.

The MMU will preheat when ejecting in case the filament you would like to eject is loaded to the nozzle. Sometimes jams happen or the MMU looses track of where filament is, so it will always do this to stay safe.


MMU errors result in the print getting paused. The printer will keep the bed at temperature until you return to resolve the issue so the part won't delaminate. The extruder will be turned off to prevent further issues though.

MMU Jams

If filament jams in the feed tubes the MMU may not be able to retract it. In this case, the coupling on the MMU may need to be removed to resolve the jam. Please report a jam to the 3D printing stewards.

Filament breaks in feed tubes

Most issues like this can be avoided by using good quality filament that has been properly dried. PLA is particularly susceptible to cracking when exposed to the air for long periods of time.

Filament stuck in the guide tubes going into the MMU can be removed by first ejecting the filament in that tube, and then feeding another material like ABS, PETG, or nylon into the tube to eject any leftover pieces of filament.

Filament stuck in the feed tube going from the MMU to the nozzle will require some disassembly of the printer. Please contact a 3D printing steward for help with this.

MMU Error Codes

Prusa's website has a full set of troubleshooting guides on the MMU3's error codes. If the error requires maintenance or tools, please consult a steward before proceeding.

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