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We added a new tool to our virtual belt - the Prusa Multi Material 2S upgrade kit (MMU2S). We’ve had our eyes on the MMU2S since February, but put off ordering due to the lengthy lead times. Lead times dropped recently and we finally placed an order!
As excited as we were and confident with the Prusa brand our initial impressions were underwhelming. We have assembled three i3 MK3 kits and two i3 MK3S kits without issue and all five printers performed amazingly out of the box. The MMU2S is a different experience all together. The instructions, while clear, forked several times depending on whether you were upgrading from a MK3S/MK2.5S or MK3/MK2.5 which lead to a slower overall build as we flipped back and forth in the manual ensuring we were on the right step. And there was this curious, little feature - a razor blade to cut the strings produced by the extracted filament. The seat for the razor is barely present, nothing more than a groove, which lead to a major issue right away.
The razor would slip out of the blade-holder and create a cut on the front-PTFE-holder (pictured above right). This happened more than once and finally cut so deep it created a jagged edge which required the front-PTFE-holder be reprinted to prevent future jams. We weren’t the only ones who encountered this problem - note the 24 comments at Step 21 in the Pulley Body Assembly chapter. We took a suggestion from a few commenters and added a drop of super glue to the razor before securing it with the blade-holder and reassembling with our reprinted front-PTFE-holder.
Although we were able to resole that issue we encountered another one which again seemed out of character for the Prusa brand. The main draw of the MMU2S is its ability to print five different filaments at once. To facilitate this capability, Prusa includes five spool holders and what it calls a buffer assembly. The spool holders work well enough - they provide a smooth glide for the spools as they unroll. But, the buffer assembly is awkward to say the least. The idea is each filament has it’s own layer through which it can glide from spool to PTFE tube to MMU2S and by default the buffer assembly is affixed to the back of the MK3S which creates a logistical challenge. To change filaments, one would have to reach behind the printer and pull or push the filament through the PTFE tubes attached to either side of the buffer. Naturally, the filament wants to curl which means it doesn’t slide straight from one side of the buffer to the other. Under normal circumstances this would become a very frustrating process when swapping filament colors.
Our guides work pretty well, but the MMU2S is still prone to jams and requires a lot of babysitting. Fortunately, Prusa has incorporated some really great error detection into the MMU2S - the printer will kindly notify you that MMU needs user attention if there’s an issue retracting or inserting filament during transitions. The MK3S will even power down the hotend and then reheat automatically once you’ve intervened. So, despite the frequent jams we’ve yet to experience a true print failure.
It probably goes without saying, but print times are considerably longer due to the time it takes to constantly swap filaments. And the filament wipe towers produce substantial waste; in the case of the pink sheep the wipe tower was larger than the final print!
All that being said, when the MMU2S is working it is a sight to behold - it really complements the MK3S; print quality hasn’t suffered in the least! Even if the learning curve has a longer tail, the MMU2S will really add value to our print farm. We are putting it through the paces now printing a cheeky smile and some 80’s style sunglasses for legü. The latest version of PrusaSlicer is a cinch to operate; you can easily place complicated multi-part STLs and select their respective filament colors without issue.
We are excited to have the MMU2S in-house despite the issues we outlined and we look forward to mastering its setup and printing jam free!