Ask questionsMMU2S Single mode filament selection inconsistency between Slic3r and printer



Operating system type + version

Windows 10

3D printer brand / version + firmware version (if known)

Prusa MK3S + MMU2S firmware 3.7.0-2201


Not sure where the problem lies, or if it's an integration issue between Slic3r PE and the firmware. When I select "Original Prusa i3 MK3S MMU2S Single in Slic3r PE, then go to Print Settings, under Extruders I have the option to change the extruder number. In this case I changed it to 4 for everything, because I wanted to use the filament loaded in filament slot 4. When I go to print the file, I'm given the opportunity to select the filament at that time. It seems like regardless of what I select, the filament in position 1 prints (I tried "filament 4" and I tried "filament 1", both yielded filament 1).


  1. In Slic3r PE, select MK3S MMU2S Single for the printer
  2. Navigate to Print Settings in the top bar
  3. Navigate to Multiple Extruders in the side navigation
  4. Change the all the value in Extruders to something besides 1 (e.g. 4)
  5. Slice and export the g-code
  6. Print the file
  7. Note you're prompted for the filament to use, select anything besides 1 (e.g. 4)
  • Expected Results Filament 4 will be used, either respecting the Slic3r selection or the printer selection

  • Actual Results Filament 1 is loaded

Is this a new feature request? No

Project File (.3MF) where problem occurs

So far as I can tell, literally any file sliced exhibits this behavior.

This may be "fixed by documentation" or a tooltip or something, as a new user of an MMU it's not at all clear how selecting an extruder in Slic3r PE relates to selecting a filament on the printer. The current slic3r docs have:

For single material prints, where the secondary extruder is to be tasked with a particular extrusion, the Multiple Extruders section of the Print Settings tab gives the ability to assign an extruder to each extrusion type.

which doesn't make much sense to me. Why would one use multiple extruders for a single material print? Different nozzle sizes?


Answer questions bubnikv

Reading through all of this, what I'm understanding here is "Slic3r in MMU2S Single mode will always only use filament #1", regardless of what's in the "Print Settings > Multiple Extruders" tab (ignored during Single mode?)

that is correct.

or the Tx code in the "Printer Settings > Start G-code" box (printer will ask you for an extruder, then ignore whatever you select?)

Slicer knows nothing about what is happening on the printer. So Slicer will use parameters of the one and only filament profile active for the MMU - Single printer profile, and it will generate a G-code for the printer, where this Tx is included. The rest is handled by the printer, it will ask the user and load one of the filaments through the MMU unit.


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