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BVOH not unloading reliably  

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Kryssie
(@kryssie)
Trusted Member
BVOH not unloading reliably

Hi,
I'm trying to print PLA with a BVOH support.
The BVOH loads and unloads way faster than the PLA, and this leads to unreliability, as the head gears expel the filament but the MMU gears don't always grab on and thus eats a half moon into the filament and 'requires user attention'. Not good for 44h print.
Does anyone have any suggestions about how to fix this?

Thanks 🙂

Fair farren

Posted : 11/03/2019 5:45 am
AndyB
(@andyb)
New Member
Re: BVOH not unloading reliably

Is it grinding at the MMU or at the main extruder? I've seen ABS grind at the main extruder when there's a lot of retraction involved. I had to disable retraction on the print to get it to run.

If it's at the MMU, try recalibrating the load/unload distance (I think it's referred to as "bowden tube calibration"). I had mine set longer than it needed to be on one position and it lead to this behavior. If that doesn't work, try fooling with the unloading speeds in the filament settings.

I'm having a different problem with BVOH unloading..... About 40% of the way through a print it kinks up in the main extruder (see picture). Any ideas? I never see this on ABS, PLA, HIPS, or PET. Only on BVOH and PVA.

Posted : 14/03/2019 6:09 pm
barbara.e3
(@barbara-e3)
New Member
Re: BVOH not unloading reliably

Hi,
Thanks for the reply. I have tried recalibrating the bowden length, made no difference. What did work is editing the code of the MMU firmware, reducing the loading/unloading speed of PVA dramatically. So far with the new loading speeds, I haven't had a mangle in the head gears (I've never had one as bad as yours though - that is really something! the best I ever got was a single loop).

My current problem is this: the filament constantly jams in the head. Whether it's undetected jams that cause skipped layers, or detected jams that cause the printer to pause and eject the filament, it make any multi-material print unreliable and I have to babysit the machine constantly. I've tried disabling the filament sensor, coz I thought it might just be over-reactive, but that lead to undetected jams (which is worse) so I did some research and found that there's a possibility that, because my printer was once a MK2S, the heatbreak is not up to the task to giving filament descent reloadable ends. I'm hoping that's it. Once Prusa pull their finger out and ship the parts I bought 7 days ago, I'll post here if the new heatbreak works as a fix for bad ends.

Posted : 18/03/2019 10:59 pm
Kryssie
(@kryssie)
Trusted Member
Topic starter answered:
Re: BVOH not unloading reliably

Hi,
Thanks for the reply. I have tried recalibrating the bowden length, made no difference. What did work is editing the code of the MMU firmware, reducing the loading/unloading speed of PVA dramatically. So far with the new loading speeds, I haven't had a mangle in the head gears (I've never had one as bad as yours though - that is really something! the best I ever got was a single loop).

My current problem is this: the filament constantly jams in the head. Whether it's undetected jams that cause skipped layers, or detected jams that cause the printer to pause and eject the filament, it make any multi-material print unreliable and I have to babysit the machine constantly. I've tried disabling the filament sensor, coz I thought it might just be over-reactive, but that lead to undetected jams (which is worse) so I did some research and found that there's a possibility that, because my printer was once a MK2S, the heatbreak is not up to the task to giving filament descent reloadable ends. I'm hoping that's it. Once Prusa pull their finger out and ship the parts I bought 7 days ago, I'll post here if the new heatbreak works as a fix for bad ends.

If you want to try the reduced loading speeds, I can tall you how if you don't know. I didn't know anything about coding, and would have been very happy for someone to have explained it, so the offer stands as a paying-it-forward.

Fairfarren

Fair farren

Posted : 18/03/2019 11:04 pm
Kryssie
(@kryssie)
Trusted Member
Topic starter answered:
Re: BVOH not unloading reliably

Just a heads-up, I have the new parts installed and will write again when I have tested the set-up for reliability.

Fair farren

Posted : 31/03/2019 3:40 am
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