Modified MMU3 chimney base for MK3S+/MK3.5S

I recently upgraded my MK3S+ with an MMU3 only to find that I had rather frequent issues with the MMU3 not being able to feed filament into the extruder. The filament would snag onto something inside the pneumatic fitting and just...not feed through. I tried multiple fitting, even from different manufacturers and I even removed the fitting and the PTFE-tube from the printer and tried to hand-feed the filament through and it still exhibited the same issue. After asking others about it, I was just told to find some alternatives on Printables only to not find any that I liked.

So, here's my own take on it: I removed the pneumatic fitting and the M5 threaded insert entirely, only using a collet to hold on to the PTFE-tube and thus simplifying the path the filament travels into the extruder. After over 500 filament swaps later and zero feeding errors, not a single one, I can confirm this approach works far better than the original one.

What you need: a basic collet for 4mm OD PTFE-tube. Not the tiny collets that Prusa likes to use that cost an arm and a leg and that are impossible to find anywhere, but the collets that are available everywhere and can be had an entire bag of for pennies and peanuts on e.g. eBay or Aliexpress. Then just print the mod and install as usual.

0.2mm layer height with PETG should work, though personally I like to use 0.1mm with variable layer height for these kinds of parts. Do make sure you've got your filament settings tuned well, so there's no gunk in or other issues with the hole the filament passes through.