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gnat
 gnat
(@gnat)
Noble Member
Under extrusion

Mine is an early batch MMU2S that I ran for about a year and then removed due to lack of use and single tool prints being a hassle and starting to act up. I recently upgraded to a Revo 6 and with PrusaSlicer 2.4's new painting tool, I figured I'd see if I can get more use out of it now. When I was running the MMU before it was with a Bondtech extruder (still using it), a standard e3d heat break, and an e3d copper block. I had no profile tweaks for slicing and the only hardware mods were the festo mods for the buffer and back of the MMU.

So I spliced in plugs for the power and data lines to make it easier to disconnect also installed a space IR board so I can easily revert the extruder functionality when desired. Then I dialed the printer as a plain MK3S back in and tested the various nozzles.

My process for reinstalling the MMU has gone shockingly smoothly to this point following this process:

  • Opened the MMU and cleaned out a year's worth of filament dust (probably why it was getting finicky).
  • Switched to the tower IR sensor.
  • Ran a XYZ calibration cube to make sure the IR sensor appeared calibrated.
  • Connected the MMU and installed the short tubes into the back (festo mod).
  • For each tool sequentially:
    • Load filament
    • Load to nozzle
    • Print XYZ calibration cube
    • Unload
  • Reinstall Prusa buffer
  • Ran all the filaments I plan to test multi-color prints with through my dehydrator for 24 hours at 120f just to make sure they are all nice and flexible.
  • Load tool 1, load to nozzle, print XYZ cube, unload
  • Load tool 2, load to nozzle, print XYZ cube
  • Print 2 color Benchy
  • Load tool 3, load to nozzle, print XYZ cube
  • Print 3 color Benchy (8 hours remaining at this time)

The XYZ cubes up to the 2 color Benchy all looked good though some had minor under extrusions that I thought had to do how I was running the filament in my pre-buffer testing. There were zero tool change issues with the 2 color Benchy.

The Benchy came out pretty gnarly with some obvious under extrusion going on. I weight it against the a Benchy printed with the Revo using the same nozzle (.4) and layer height (.2) and the dual color came in at 9.4g compared to 11.9 of the single color. I dug up an old dual color Benchy and it matched the single color's weight. I also found the purge block of that old 2 color and it came in at 32.6g compared to 16.9 for the new. When I weighed the XYZ cubes, 4g was the norm, but the tool 2 block was 3.6g and tool 3 is 3g (both post buffer addition). So clearly some significant under extrusion going on, but I don't know why. I'm not hearing clicking to suggest that it is fighting the filament in one direction or another. Anyone have ideas about where the issue might be?

Silver/Neutral = Old 2 color
Yellow = Post Revo upgrade .4/.2 print
Silver/Yellow = Bad Benchy (note: same yellow filament on tool 2 for the single color Benchy)

https://photos.app.goo.gl/wopBLkuuJv4jk98S6

 

Here are the purge blocks:

https://photos.app.goo.gl/Hp35iFu1VX9UWzHK9

Ce sujet a été modifié il y a 6 months par gnat
MMU tips and troubleshooting
Publié : 12/04/2022 1:24 am
BaconFase
(@baconfase)
Eminent Member
RE: Under extrusion

Is yellow being printed at a significantly lower temperature than gray?

Publié : 12/04/2022 5:41 pm
gnat
 gnat
(@gnat)
Noble Member
Topic starter answered:
RE: Under extrusion
Posted by: @baconfase

Is yellow being printed at a significantly lower temperature than gray?

Nope. Both are using the Prusament PLA profile (and both are PLA) which is 215 for the XYZ cube (sliced for a MK3S) and 210 for the Benchy (MK3S+MMU2S profile). The all yellow Benchy was at 215 since it was sliced with the MK3S profile.

MMU tips and troubleshooting
Publié : 12/04/2022 6:02 pm
gnat
 gnat
(@gnat)
Noble Member
Topic starter answered:
RE: Under extrusion

So I played with swapping filament paths and filaments around and what I found is that the issue appears to follow the filament. The "problem" filaments are both Inland while the filament that is playing nice is GST. Un-objectively the GST feels smoother and more supple. I know from experience that stiff/rough filament can have an adverse effect on friction in the filament path.

I happen to already have some ID 3mm tubing on order as I wanted to reroute my filament path anyway, hopefully that will help the issue.

MMU tips and troubleshooting
Publié : 12/04/2022 9:53 pm
BaconFase
(@baconfase)
Eminent Member
RE: Under extrusion

Seems weird that it would be a filament path friction issue if you can print without issue when doing a single color print.

I and one person from memory have had issues with rougher filament getting issue-causing-amounts of friction from the closed MMU cover during a print. Have you experimented with loosening or even having the MMU cover completely open during prints? Or maybe just check to make sure the MMU selector barrel is correctly rotating away when it should.

Publié : 12/04/2022 11:20 pm
gnat
 gnat
(@gnat)
Noble Member
Topic starter answered:
RE: Under extrusion
Posted by: @baconfase

Seems weird that it would be a filament path friction issue if you can print without issue when doing a single color print.

Based on today's findings, I don't think it's the path. I think it's the filament itself. Or at the least the filament isn't playing nice with the current path setup.

I and one person from memory have had issues with rougher filament

I have actually run into such issues in the past (with Inland actually) where old filament that had started to stiffen was causing all kinds of grief (breaking in the tubes, getting eaten by the gears at both ends, and excessive tails). That was before I got my dehydrator though and I haven't had issues since as long as I run the filament through a good heat cycle prior to using it (which I did in this case).

getting issue-causing-amounts of friction from the closed MMU cover during a print. Have you experimented with loosening or even having the MMU cover completely open during prints? Or maybe just check to make sure the MMU selector barrel is correctly rotating away when it should.

The selector does seem to be working as it's supposed to and I don;t recall ever running into an issue with that.

It could indeed be that while it is generally working, the tension on one end or the other might not be quite right. While the filament can be the source of extra drag and cause issues, it doesn't seem likely that it would be the entire cause of under extrusion. At least not without other symptoms (like the extruder clicking/grinding due to the filament not moving correctly). I did note, however, that the ends of the filaments all have a pretty consistent pattern on them to suggest that the extruder gears are tensioned well. That is the only tension that should be important once filament is flowing.

MMU tips and troubleshooting
Publié : 13/04/2022 12:10 am
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