Luke173
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MMU 2.0 Filament Retraction Issue

Sep 14, 2018 3:06 pm

Hello

I got the MMU 2.0 for my Mk3 last week, and assembled it that week. I then tried to print a 4 color model, but sadly no success so far.
As soon as the second color retracts for the first time, it get's stuck just bove the hotend idler drive gears. I then have to manuelly pull the filament out. All filament look like this:
IMG_1831.jpg
IMG_1831.jpg (1.89 MiB) Viewed 202 times
It looks to me as during retraction the hotend idler is pushing backwards, whereas the mmu idler is at a full stop, causing the thin part of the filament to clog the orange tube.

Has anyone else seen this?
I thought maybe my orange tube is too short, causing this. so, can anyone give me a measurement of the orange tube you have?

many thanks for your thoughts
Luke

toaf
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Re: MMU 2.0 Filament Retraction Issue

Sep 14, 2018 5:12 pm

did you do the Bowden length calibration?
thanks,
chris

peter.l22
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Re: MMU 2.0 Filament Retraction Issue

Sep 14, 2018 6:24 pm

Luke173 wrote:
Sep 14, 2018 3:06 pm
As soon as the second color retracts for the first time, it get's stuck just bove the hotend idler drive gears. I then have to manuelly pull the filament out. All filament look like this:

It looks to me as during retraction the hotend idler is pushing backwards, whereas the mmu idler is at a full stop, causing the thin part of the filament to clog the orange tube.
Well, something is mashing the end of the filament for sure. It's a good idea to do the bowden length calibration just in case, but I don't think that's causing this issue. The MMU should be completely disengaged when the extruder is backing out the filament, leaving only a little friction. If the MMU is engaged and fighting the extruder I could see how this might happen, but if that was the case I think you'd have bigger problems.

Just to eliminate some variables....What happens if you print a small model in single material mode? At the end of a single material print the MMU should unload the filament just like it does when changing materials. Do you see the same problem then?

khalil.n
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Re: MMU 2.0 Filament Retraction Issue

Sep 14, 2018 7:40 pm

@Luke173

I've had problems with my MMU2 as well.
Most were standard tweaking tensions and stuff like that.
Other issues were minimized using Prusa and Hatchbox filament instead of Inland filament (stringing leading to jams).

Still trying to get a complete print no layer skips.

Luke173
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Re: MMU 2.0 Filament Retraction Issue

Sep 16, 2018 7:22 am

good day, many thanks for your thoughts.

Boweden Calibration: No, i didn't do this, how can I do it? I don't find it in the assembly manual.

Single color print: No, at the end of a print the filament does not unload back into the MMU here, it stays in the hotend idler. But it does not show any error from the machine at that point, so I have to assume it's the way it is.

I also thought about the material causing this, but it happens with every color PLA i have, and I don't really want to try ABS right now.

Thanks again
Luke

peter.l22
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Re: MMU 2.0 Filament Retraction Issue

Sep 16, 2018 3:23 pm

Luke173 wrote:
Sep 16, 2018 7:22 am
Single color print: No, at the end of a print the filament does not unload back into the MMU here, it stays in the hotend idler. But it does not show any error from the machine at that point, so I have to assume it's the way it is.
At the very end of a single color print the MMU should unload the filament. Is it not unloading the filament at all, or is it trying to unload and getting jammed?

If it's not trying to unload at all, then check to make sure you flashed the MK3 firmware with the MMU version, not the standard version. It's possible the printer has the wrong firmware.

annez
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Re: MMU 2.0 Filament Retraction Issue

Sep 17, 2018 8:04 am

Luke173 wrote:
Sep 16, 2018 7:22 am

Boweden Calibration: No, i didn't do this, how can I do it? I don't find it in the assembly manual.
It's hidden in the manual.

https://manual.prusa3d.com/Guide/Status ... 62?lang=en
MMU2 Troubleshooting - Status LED indications explained - Step 4

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