MMU2 Upgrade
I am a retiring engineering tech/R&M technician in a semiconductor fab. Having much experience
(40+ yrs.) in machine diagnosis and repair, electronic design, new product development. blah, blah.
This is my first experience with additive machining and the Prusa MK3S is my first such machine.
Very impressed with the printer and so far any problems have been my fault. Having the printer for barely a
month, decided to upgrade to MMU multi filament configuration. Installed upgrade and had various issues.
Looked on web and saw a "you tube" review describing up grade as "not ready for prime time". What I have come to understand is that having no experience and assembling is very dangerous as the perspective is "how" not "how well" you need to do something. As I see problems I have been able to address them, so far they have
been due to poor assembly due to "just do it "not be care of this" as experience works but is not there.
I would like to say the upgrade is amazing, trying to explain all is tough.
Improvements:
(1) Instructions should specify very clearly what to do and should have no contradictory pictures (i.e. screws shown installed from opposite direction with nut ending up on wrong side).
(2) Leave guess work out, specify which roller goes in first because it takes too much thought and good vision, and it takes creativity to pull pins out onced installed.
(3) Specify tightness, especially if threads are plastic or if item needs to be secured firmly.
(4) Who came up with that crazy Filament Buffer? Interesting concept, don't like it though.
Very difficult to thread and, if there are problems, a real pain to grab correct filament. Took mine off! Better concept would be like the tip of a fishing rod. Line is pulled to MMU and the tip (sticking up like a fishing pole has enough Young's modlus (flexible travel/springiness) to act like a fishing pole and lower as line is pulled. When the line is "ejected" the rod merely flexes back with enough force to take up the slack. This can be implemented in many simplistic ways, such as a spring steel wire with a loop on the end, a piece of "poly-pro" tubing with a spring steel wire inside or even a piece of filament with a loop on the end as in doubled back into the tube. With the existing diameter of the spools, the rod could be proportionally long enough to easily compensate for the line returning from the MMU.
(5) The bondtech gears need to be adjusted properly for alignment and tension. The drum bearing for the MMU was not fully seated and "wobbled" when rotated. Inserting a drill bit (properly selected from an index of drills, made sure the bearing was coaxial, seated properly, and drum rotated smoothly (motor removed).
(6) Found the Extruder bondtech gears had insufficient tension, adjusted with great results. Would be nice if a procedure and/or simple spring strain gauge was made to measure force required to make slip for the extruder and all the individual MMU bondtech gears.
Disclaimer: Being "a newbie" and not knowing what I should be considering, yet, I may regret some of the above, however I believe that the MMU2 upgrade is ready for "prime time". Unfortunately it is hard as a vendor/manufacturer to predict what someone doesn't "see" and also to design something without the knowledge of a better concept. I wonder how much better it would have performed had "professionals" assembled this Mk3s w/MMU upgrade!
Good job overall, very impressed with the design, electronics implementation, quality/timely shipping,and great customer service! What I have seen, Prusa is truly a "world class" company! Don't let us down!
James H.May, Parker, Texas