MMU2S - My Journey  

MMU2S - My Journey

I love my Prusa MK3.  My wife bought it for me for Christmas as a kit. It took me 12 hours to put together (I was careful and took several days), and only had one small error on the first test (X Axis – cable ties were sticking out).  I’ve had a blast printing all kinds of things that come out great.

My wife also purchased me the MMU2, but it wasn’t scheduled to arrive until April (then May).  I was so excited.  By the time I got it, they had already updated the MK3 to the MK3S. I mistakenly also purchased that upgrade despite all the parts being included in the MMU2S.

Once again, I took my time putting the MMU and the MK3S upgrades on my rig to make sure that I didn’t make any mistakes.

Needless to say, things did not go as well. It has taken me over a month of spare time working with the MMU2S to overcome the issues associated with multi-material printing. There were jams, stripped BondTech gear screws, tube placement and connections, etc. 

Unlike the MK3, the MMU2S requires a significant understanding of the mechanism and the setting to make things work correctly.

First off…you will want to print out a few upgrades from Thingiverse:

1) PTFE Holder M10 Passthrough Adapter by 8orge.

https://www.thingiverse.com/thing:3233579

This is design uses M10 couplers and is a MUCH better way of getting filament into the MMU2.  You avoid crimping the tubing and it is much easier to remove. I hope Prusa includes this type of fix in their next upgrade.  If you prefer M6 couplers go here:

https://www.thingiverse.com/thing:3652406

2) Prusa MMU2 PTFE Tube Separator by fucosk.

https://www.thingiverse.com/thing:3166394

This design keeps your filament straight going into the MMU2 unit.  It will help the filament go into the BondTech gears.  There are several different designs of tube separators, find the one that works best for you.

3) MMU2S-Buffer-M10x1-PTFE_Extension by clintfisher.

https://www.thingiverse.com/thing:3545935

Anyone that has tried to use the buffer as designed will have problems loading the filament into the MMU2 unit (unless they have very small/thin fingers).  This design gives you more space to push filament through, and it uses M10 couplers instead of crimping the tubes.

Tip: To help push the filament inside the buffer from the input to the output, I use a wooden chopstick and hold the pointy end in my hand. This is the perfect size to fit into the buffer and makes it much easier to load curving filament.

Another issue I had is well documented in this forum.  My IR Sensor was not reading correctly in the extruder. I had to “shave off” a bit of the Extruder-idler-mmu2s door flap at the top to get it to sense the filament correctly.

Once I got all of these changes in place, I was able start printing.  However, this was not the end of my troubles.

First, I somehow managed to erase the MMU2 settings on the length of the load down to the extruder. So I followed the Individual Filament Calibration instructions:

https://manual.prusa3d.com/Guide/Service+menu+-+Individual+Filament+Calibration/842

I was still getting a lot of “MMU needs attention” stoppages during tool changes.  After several attempts to understand the issue, I realized that it is often caused by the stringing of the filament.  Like most people, I have several different brands of PLA/PLA plus, and each has different properties.  Also, old filament may be more affected by moisture. If you are not getting clean pointy tips without stringing, the sensors will not trip, and the print will halt.  You may also have a buildup of junk in the FINDA sensor housing or the extruder.

To make my prints work, I have to check each filament by doing a practice print that shows all the tool changes. Then I adjust the temperature, cooling moves, and ramming settings on each filament until I get a good tip on each.

I also bought a filament dryer to make sure that the moister is removed.

I’ve just started getting some completed multi-color prints and even have had some success with soluble material. I didn’t want to pay $60-$100 buck for BVOH, so I got a spool of PVA. This is really tricky to get the temperature, cooling moves, and ramming set correctly, along with the correct purging volume. But it can be done.

So, is getting and setting up the MMU2 worth it?  For a while I wasn’t sure if I could get it working. Thanks to the valuable information on these forms and contributors to Thingiverse, I am starting to produce the prints I was hoping for.  I know that I have not overcome all possible issues yet, but it gives me something to tinker with.

If you are looking for an out-of-the-box multi-material printer that works with minimal issues, you are going to be frustrated and disappointed. However, if you put the time and effort you can achieve some wonderful prints.