MMU2S Extruder idler failure and fix
First I want to ask if I am the only one having this issue. Twice I've had to replace the MMU2S Extruder Idler. The problem is the shaft is about 2.3mm too short so only rests on half of its seat. The room the printer is in is not air conditioned so it gets a bit warm which probably also contributes. After 100 hours or so of operation, I start to get filament change failures because the shaft starts to sink into it's seat and the printer fails to detect filament. The firmware kindly pauses and I am able to resume the print after re-calibrating the IR sensor (well done, Prusa) but this should not be happening. Anyone else running into this problem and how did you address it?
The third time around I decided to try to fix it. I did not have any hardened 1/8" shaft around to make a longer shaft but my local hardware store did have some 4mm brass hobby tubes which slid over the provided shaft snugly. So I printed a new idler with holes enlarged to accommodate it. Not quite to 100 hours yet, but I've been inspecting it and see no signs of distortion:
https://www.prusaprinters.org/prints/5426-reinforced-mmu2s-extruder-idler
RE: MMU2S Extruder idler failure and fix
Oh, and you may not realize this is contributing to your change failures if you don't have this mod:
I first became aware because I saw the indicator light flickering when it should be steady-on when filament is present. If you are experiencing issues with filament changes, remove your door and look into the hole the shaft occupies. In my case, the shaft had sunk almost halfway into its seat.
RE: MMU2S Extruder idler failure and fix
i'm not sure i understand.
the shaft is a bit too short yes so you need to be careful when you push it in so it has reached the plastic on both sides.
but the shaft should not rotate at all since you have two ball bearings inside the bondtech idler gear, so how can the shaft itself grind against the plastic?
or do you mean that the bondtech gear is grinding against the sides ?
RE: MMU2S Extruder idler failure and fix
It does not rotate - it is quite snug. What is happening is it starts to distort the hole it seats in from the pressure of the spring pulling it into the filament. First time it failed I figured I must've tightened the spring too much so I kept it almost to the point of slipping after that but still had it fail again. I think if the shaft were longer and utilized the full length it might not have failed.
(True, great care must be taken to maximize the contact area on both sides when inserting.)
Another factor that may be contributing to my failure rate is I am almost exclusively printing with PETG (90C bed, 245C extruder) and have the printer in an enclosure but I leave the door open when printing PETG to keep the heat from building up too much. I suspect the part got a little soft from the warm environment.