Mk3s & MMU2s Filament Loading Problem  

RE: Mk3s & MMU2s Filament Loading Problem

Hi,

Most common issue is not properly setup IR sensor. I would start there. Display the sensor state in the menu. Wiggle around the IR sensor, move the whole top part, push against the idle door screw and check if the value changes randomly. It should only change if the door is moving significant amount.

Based on your description it's hard to guess why you canceled your first attempt or why/when you tried load to nozzle. Usually you can fix the issue and proceed with the print, even if you have load/unload or any other issue. If you just completely lost, then I would suggest to contact Prusa Live Support. They can guide you through the most important steps.

RE: Mk3s & MMU2s Filament Loading Problem

I abandoned the 2 prints because no matter what I tried I couldn’t get the filament to the nozzle! 

Having read quite a bit more last night I removed:

1. The knife blade, this has enabled the selector to move much more freely and my experience earlier had demonstrated how ineffective it was. I don’t know why this feature isn’t based around a rotary cutter blade, at least that cuts in both directions; it would also create less drag on the selector as the blade would rotate!
2. The whole print buffer assembly!

This has at least allowed me to print single colours through the MMU.  I am currently printing the parts I need for auto rewind reels to give that a try as a replacement for the buffer, I hadn’t a clue where I was going to put it anyway!

RE: Mk3s & MMU2s Filament Loading Problem

Posted by: derek.a.austin

I abandoned the 2 prints because no matter what I tried I couldn’t get the filament to the nozzle! 

That sounds like an IR sensor issue.

RE: Mk3s & MMU2s Filament Loading Problem

Thanks nikolai-r, I will certainly check that out before I try any further multi colour prints.

RE: Mk3s & MMU2s Filament Loading Problem

Posted by: derek.a.austin

After several resets of the MMU and printer, including reset buttons and power downs the MMU now just whirs and clicks a few times and does nothing! It looks like the idler is not operating as it should.

Where would you start with solving this one? All serious replies most welcome!

Regarding the MMU idler, are you sure you haven't over tightened the two screws at the top of the MMU ?
if the idler is just causing noises then i bet it can't move and this will cause all kinds of problems.

Also check how you positioned the 5 short ptfe tubes in the mmu, where is the chamfered side pointing? chamfered side should be towards the 5 gears below the idler that pushes the filament forward and out the selector.

RE: Mk3s & MMU2s Filament Loading Problem

Posted by: torbjorn.j3

 

 chamfered side should be towards the 5 gears 

I think you have this backwards.

I've seen a few people confused by which way OUT is referring. But the chamfers should be AWAY from the gears. This is for when filament is retracted back to the MMU. It supposed to help the tips get back inside the tubes. Once the filament is retracted during a print, the tip should be just inside or toward the middle of the tubes. It should not come out the back side. Having the chamfers facing the gears might help with initial loading but would have no effect during a print. You can see more clearly in the full size picture HERE.

RE: Mk3s & MMU2s Filament Loading Problem

well... perhaps i got it wrong but it works better with chamfered side towards the gears.

for example if you have just cut the tip off then you don't get a flat(ish) filament against a flat side of the ptfe tube causing filament to get stuck on its way out (mmu unable to push out filament with grinding as a result)

once filament comes back from extruder towards mmu the "blob" is round and small enough to make it back without problem and then the tip is sharp to make it out next time.

RE: Mk3s & MMU2s Filament Loading Problem

That makes sense. Maybe we can get the best of both by having BOTH sides chamfered?

RE: Mk3s & MMU2s Filament Loading Problem

Posted by: troy.p3

That makes sense. Maybe we can get the best of both by having BOTH sides chamfered?

Exactly what i was thinking too, plus it avoids problems since you can't get it wrong.

RE: Mk3s & MMU2s Filament Loading Problem

I have just, albeit reluctantly, removed the MMU2s.  I have not been able to resolve the filament loading and unloading issues to make the unit reliable enough to warrant leaving it in situ! 

I had reached a point where 3 out of four prints failed at various stages due to filament feeding issues.

I will keep an eye on this forum until I see reported improvements, but it would seem to me that the relationship between the extruder gearing and the MMU2 feed system needs looking at.  More than once the MMU has ground the filament so badly that it is not being gripped at all!

RE: Mk3s & MMU2s Filament Loading Problem

Posted by: derek.a.austin

I will keep an eye on this forum until I see reported improvements, but it would seem to me that the relationship between the extruder gearing and the MMU2 feed system needs looking at.  More than once the MMU has ground the filament so badly that it is not being gripped at all!

Maybe you've experienced this issue: https://github.com/prusa3d/Prusa-Firmware/issues/2086
If you watch the extruder gear while filament change, you will see that it's pulling inside (after 2 seconds wait time) after unload completed. During this time frame the printer expect that MMU2 is fast enough to pull the filament out. For me it's sometimes not the case. The result is that the extruder gear is holding the filament while the MMU gear is grinding it down. So I increased the wait time to 4 seconds and since then this issue was no issue anymore.

I made a pull request and using self compiled version (with this change) successfully. But so far heard no feedback from developers or intentions to merge it.

RE: Mk3s & MMU2s Filament Loading Problem

You could well be right but it's beyond me to fix it!  Hopefully the next firmware update will address some of theses problems!