MM2s Jamming  

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zargnut
(@zargnut)
Active Member

Hi,

Just installed MM2s on MK3s. In testing all sensors are working, all filaments will feed and unload. When using single mode, it prints fine. I printed a few items with 2 filaments that required around 85 filament swaps. It is consistently jamming on unload. 

Most of the time It seems to unload fine, but is showing a fast flashing red light. Pressing and holding the middle button does nothing, it cycles and then flashes red again. Hard cycling the machine resets everything and it works again. ie there is no mechanical obstruction. 

I am using prusament PETG and am getting long fine strings about 1.5-2cm at the end of the filament on unloading. I tested raising the temp to 235 - worse. Tried reducing temp to 227 - no change. Tried increasing cooling seq to 3. No change. 

Are the jamming/errors due to the stringy filament at the end? Any advice on how to modify settings to mitigate this? 

Can I create different temp/load parameter profiles for specific filaments - as they don't seem to be affected the same way with regard to stringing. 

Posted : 25/12/2019 3:24 pm
rob.w5
(@rob-w5)
Trusted Member

The long strings are most certainly causing the problems.  When you assembled the MMU2 you dropped a steel ball into a hole.  That steel ball needs to be in proximity to a sensor when there is no filament loaded.  The filament (and strings) can prevent the ball from dropping down into place, so your printer thinks there is a filament jam.
There are a couple ways strings can cause problems.  The first is causing a horizontal bridge that prevents the ball from dropping.  Another is for the string to get caught between the ball and the side of the cavity, locking the ball in the up position.

The fast and easy fix is to take the top of your MMU selector unit off (Two M3 bolts) and blow compressed air in the hole.  While you are at it, blow air into any orifice you can access.
A more difficult solution would be to look online (and look through these conversations for links) for an enhanced Extruder Selector.  Some of these have larger cavities to hold any strings that drop off the tips during unloading/loading, some have magnets to give gravity a bit of help dropping the ball into place, some have both.  One uses a magnet that came with your MMU2s/MK3s kit but is unused, others require smaller magnets.  I tried using the one with the unused magnet, but found it was off dimensionally and would not successfully load filaments 3-5.  So if you go for a magnet based improvement, I would recommend expending the effort to get the one with a magnet you will have to find/buy.

Posted : 30/12/2019 5:48 pm
zargnut
(@zargnut)
Active Member

@rob-w5

Thanks. I will look for that mod with the magnet.  I was able to get it to print after resetting the printer.  

Do you have some guidance on tweeking the settings to reduce the stringing at the end of the filament which occurs upon unloading. All i found on the instructions were vague instructions to modify filament temp, and if that fails... to increase cleaning moves.. both of which I have done with inconsistent success.

thanks

dan

Posted : 30/12/2019 6:08 pm
Nikolai
(@nikolai)
Noble Member

@zargnut

It's pretty tough to create nice filament tips with PETG in general.  Based on my experience I have a jam every ~100 filament changes with PETG. The fine strings tend to block something. You're printing PETG with pretty low temp (230C) . You can easily go up to 255C. In the higher range, you will get finer strings. Had no success to avoid it completely with this filament type. 

I would recommend to print in PLA first. Temperature and cooling moves are the most efficient ways to change the shape and you should see the difference with PLA. 

Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram...
Posted : 30/12/2019 10:14 pm
toaf
 toaf
(@toaf)
Noble Member

i think I changed the speed for the ramming for petG.  its been awhile.. but that might help

I have a Prusa,therefore I research....
Posted : 31/12/2019 3:43 am
zargnut
(@zargnut)
Active Member

Thanks. 

Is there a glossary somewhere which defines all these settings.. Ramming suggests to me the feeding speed into the extruder. The stringy head already exists as it is created when the filament is unloaded... Does slowing the ramming speed just reduce jamming with a stringy end? 

 

Posted : 31/12/2019 3:11 pm
toaf
 toaf
(@toaf)
Noble Member

i would try slowing it first. but I think I ended up speeding it up for some type of filament.  I just don't remember.

the ramming is the bit it does before (during) unload. it should shape the tip of the filament.

I have a Prusa,therefore I research....
Posted : 31/12/2019 9:50 pm
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