MMU2 - another solution for layer skipping due to filament length  

Re: MMU2 - another solution for layer skipping due to filament length

I've had great luck with getting the speeds matched - as you mentioned, the solution is well over a month old, it would be AWESOME to get some official buy-in from Prusa on the stuff that works so we stop answering the same five questions over and over.

If you want to use your springs without risking the sensor, you could print/add standoffs under the bolt head (inside the spring) to keep the screws from bottoming out. I can draw it if you need, but like, a 2.9mm ID, 3.5mm OD tube that's equal to the extra length of the screw you are using.

Re: MMU2 - another solution for layer skipping due to filament length

Just installed the upgrade after the printer paused due to a failed load. The rest of the print had no issues afterward. I printing another to see how an entire print does, and I will post my results once it finishes.

Re: MMU2 - another solution for layer skipping due to filament length

I wonder... I didn’t have any skipped layers using 100% Prusament until I got to the end of my roll. Is there a way it’s backing off too far in the MMU, and then not able to bridge the gears again?

Re: MMU2 - another solution for layer skipping due to filament length

I don't know if this is relavant to this specific topic, but I found that one of the spool holders was creating a lot of resistance. I took the original spool holder that came with the MK3 and ziptied the old PTFE tube that I removed from the hotend to the frame and this fixed almost all of the layer skipping. It has only had one mix up, which it caught. I still had to restart the print (because it was stuck in the extruder which had cooled down so I couldn't unload it)
Other than that I haven't had any issues with the print.

brillant idea ..... Thank you very much

Thank you very much, just installed and tested.
It works fine and filament change is now smooth without damaging the filament with the bondtech gears in mmu2.

Re: MMU2 - another solution for layer skipping due to filament length

Thanks for this great Idea !

I expanded the idea a little. I got longer screws 30mm or so, because they have no thread under the head.
Drilled out the printed part and put in 2 short brass tubes, with 4mm OD and 3.2 mm ID.

with this i have like 5mm "buffer".

I adjusted the lentgh calibration to be an little bit more than necessary and it works great.

Re: MMU2 - another solution for layer skipping due to filament length

How's everyone's experience with this mod, has it resolved your layer skipping / filament grinding issues?

Re: MMU2 - another solution for layer skipping due to filament length

How's everyone's experience with this mod, has it resolved your layer skipping / filament grinding issues?

So far I haven't had any problems with filament grinding at all. Now the only problem is the occasional increase in filament resistance (for no apparent reason, I fixed with a piece of PTFE tube and a zip tie).
Since the mod, I have done a small handful of prints and only 1 of them failed. I would say that's a huge improvement.

Re: MMU2 - another solution for layer skipping due to filament length

So far I haven't had any problems with filament grinding at all. Now the only problem is the occasional increase in filament resistance (for no apparent reason, I fixed with a piece of PTFE tube and a zip tie).
Since the mod, I have done a small handful of prints and only 1 of them failed. I would say that's a huge improvement.

That's awesome, thank you for your reply. I'm having a 100% failure rate due to missed layers or ground up filament. This mod seems like a no brainer but wanted to hear some feedback before I attempted to even bother with the MMU again.

Re: MMU2 - another solution for layer skipping due to filament length

How's everyone's experience with this mod, has it resolved your layer skipping / filament grinding issues?

So far I haven't had any problems with filament grinding at all. Now the only problem is the occasional increase in filament resistance (for no apparent reason, I fixed with a piece of PTFE tube and a zip tie).
Since the mod, I have done a small handful of prints and only 1 of them failed. I would say that's a huge improvement.

How does this zip-tie thing look like? Can you share a photo of this?

Re: MMU2 - another solution for layer skipping due to filament length

How's everyone's experience with this mod, has it resolved your layer skipping / filament grinding issues?

So far I haven't had any problems with filament grinding at all. Now the only problem is the occasional increase in filament resistance (for no apparent reason, I fixed with a piece of PTFE tube and a zip tie).
Since the mod, I have done a small handful of prints and only 1 of them failed. I would say that's a huge improvement.

How does this zip-tie thing look like? Can you share a photo of this?

It's kind of a botch solution but here is a picture of the setup. I took the piece of PTFE tube that you are supposed to toss out (from the extruder upgrade) and simply zip tied it to the upper z mount.

I would recommend using a better method but I did this to test if the spool holder was the issue and it definitely was.

Re: MMU2 - another solution for layer skipping due to filament length

Try something like: https://shop.prusa3d.com/forum/-f0/wallet-style-filament-slack-take-up-t25027.html Lots of us have found the OEM retract mechanism not to be sufficient.

Re: MMU2 - another solution for layer skipping due to filament length

I'm going to install this ASAP. I've found that you need to set the feed distance further than recommended in order for the gears to engage with the filament consistently. Unfortunately this has the grinding issue at the MMU that we've all heard.

What I don't understand is why the gears of the extruder aren't rotating when the filament comes down so they can "accept" the filament as it reaches the end of the feeding distance. Instead they're just sitting there stationary to be rammed into. If they were rotating at the correct rate the filament could smoothly feed in without a need for this mod. The extra few millimeters wouldn't matter, as they'd get primed away in the prime tower. Can anyone explain why they don't do this, or just haven't bothered to yet? Seems odd...

Re: MMU2 - another solution for layer skipping due to filament length

these springs have made a huge difference for me.