MMU3 for Mk4 setup in PrusaSlicer 2-7-4
Looking for a link to official product information or answers on how to set up my Prusa slicer profile for the MMU3 I just installed on my Mark 4. My primary question is that in the profile set up there is a default in the printer tab to show five different extruders. The Mk4 only has one extruder and the MMU3 provides access to up to five filaments. There is an option to say there is only one extruder access, but that doesn’t work for me in selecting multiple colors for a model in Slicer. If I leave the stock install printer model with five extruders and assign different colors to the extruders then the multiple colored print works. I’m assuming there’s someplace in Prusa literature that references the five extruders are really virtual extruders and that’s how slicer handles knowing when to switch filaments/colors on the MMU3 but I’d like to read about that to know I’m thinking the right way, plus I’m sure there’s a variety of options and features that particular article or knowledge Base wood cover.
Could someone please point me to such literature and if you would confirm, please, that virtual extruders, though they are not labeled that way in Prusa slicer, are the way the MMU3 handles instructions for the different filaments? Thanks in advance!
RE: MMU3 for Mk4 setup in PrusaSlicer 2-7-4
Good Morning Dave,
MMU3 User manual, online version https://www.prusa3d.com/downloads/manual/prusa3d_manual_mmu3_en_102.pdf
Yes Virtual extruders are the way that MMU3 manages 5 different filaments
Below, is a part that I was making, and there is an unsupported area between the two lower round holes
I Tried adding supports, in PETG, the same material as the model was printed in, and found that in this case, the support was very difficult to remove and left a messy surface finish.
As I Have an MMU3, but I don't have any BVOH, or PVA, or Scaffold filament
and, I don't like the prices...
I chose to use PLA as the Support Interface...
PLA and PETG are not good bed pals... they do not like sticking together... so to reduce the number of layers where the nozzle would be alternately purging the two Filaments, I made PLA the support interface only, and all of the rest is PETG (Poor Purging can lead to a weak mix of PLA And PETG so increasing purge volumes helps address this potential issue, at the expense of a larger purge tower. reducing the number of layers where filament changes occur, further improves the chance of Success.)
I Set PETG as filament one, because, it would be the first filament I was printing in the model, MMU typically prints filaments in ascending numerical order anyway, and it was the easiest one for me to change...
the remaining filaments were left as PLA, from the Previous job setup.
as you can see, there is a single layer of Yellow PLA Filament causing an interface layer between the Grey PETG Parts.
PLA and PETG don't like sticking together and the first print was unsuccessful. so I increased the density of the supports and reduced the separation to 0mm to encourage bonding, and the next print was a total success.
after printing, I Flexed the model off the build plate and both parts remained together, however when I flexed the model away from the support material, the support material popped out easily. I did two prints, both were successful, the first print left some PLA on the model and some PLA on the support, the second model left all of the PLA on the model, however the PLA was very easy to remove, and left a much nicer undersurface on the finished model
revising settings for the various 'Virtual Extruders' is not immediately obvious... 
however if you look at the 'Filament Settings>Filament' tab, in Prusa Slicer, there is a selection box, (Hilighted in the image above) that allows you to select the settings for the individual filaments. please note that I have used higher than normal temperatures for the PLA, so that the temperatures are nearer PETG temperatures, in order to promote inter layer bonding. during printing (I believe this is also more likely to promote good purging during filament changes)
I will include a copy of my project file for you to look at it may help you sort out the settings.
Regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE:
Thanks very much Joan. I read through the manual and that helped. I see there is a setting in the right panel of the printer tab to select multi-material through 1 extruder right below where it says there are 5 extruders. A bit goofy of a set of descriptions that kind of contradict but I was overthinking it, knowing about the XL model. That helped thank you!
Also related to your supports example, I read where, the manual says you should also use Extrudee 5 for soluble supports. I wonder if you use that channel for supports regardless of the material type if that would help Slicer set up a model better?
Thanks again for your help!