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Intermittent loss of extrusion during print  

Active Member
Intermittent loss of extrusion during print

I have a MK3S+ / MMU2S / Bondtech BMG / Mosquito Magnum that is experiencing intermittent loss or decrease of extrusion both during the printing process or sometimes immediately after a filament change.

(the first layers in the above prints were very clean and consistent)

I am using 3mm ID PTFE tubes with mods allowing M10 push fittings that allow the tubes to feed as far into the MMU2 as possible.  I have encountered a variety of load failures that I have worked through to get to this point and it is loading and unloading very reliably.  One of the fixes to get loading to work was to add a separate voltage converter feeding 5.2v to the MMU2 (see separate thread around a discovered hardware issue).  Adding that completely resolved the various loading issues I was encountering.  Before the change, I had between a 50%-100% load failure and got major amounts of grinding / clicking.  With the fix, almost all of the grinding / clicking went away, but not all.

I do still get some grinding and clicking.  Additionally during the loading process during the brief advance / retract phase, I can see that the filament in the buffer is loading and unloading in jerks.  Here are things I have checked / tried:

  • Check for blockages / ease of filament movement (spool -> MMU2, through MMU2 / selector, MMU2 -> extruder, extruder gears -> melt chamber).
    • All paths allow for easy movement of the filament and the 3mm ID PTFE tubes have much less friction than the stock tubes that came with the printer
  • Verify sensors / calibration
    • FINDA triggers reliably and doesn't seem to show any false triggering
    • IR sensor calibrated with 1.5mm hex wrench (wiggled to ensure a solid read)
  • Check that gears (extruder and MMU2) and idler (MMU2) are secure
  • Ran cleaning filament through at 270C
  • Cold pulls (always comes out clean)
  • Printed with MMU2 disabled and filament fed directly into the extruder
    • Prints just fine - no clogs, grinding, loss of extrusion
  • Partial extruder disassembly to remove Mosquito Magnum.
    • It was completely clean after a cold pull
  • Replaced PTFE tube in top of Mosquito Magnum
    • Ensured it was exactly the right length and chamfered the top / incoming end
  • Run without a filament buffer and only short PTFE tubes entering the MMU2
  • Tried TheZeroBeast firmware on MMU2 and MK3S+
    • Filament load is much smoother - visible jerkiness reported above is much reduced
    • Still hit the loss of extrusion

I'm sure there were other tests I ran as well, but its a giant blur at the moment.  The current problem is intermittent and may not show up until an hour or more into the print (or may show up right away).  It has gotten as far as 30-50 filament swaps before encountering this.

The original filament load issue I had always felt like a feed mismatch between the MMU2 and extruder.  Given that fixing the voltage issue (which potentially impacted the stepper drivers) fixed the load issue and significantly decreased the grinding seems to support that analysis.  This current grinding seems like a lesser version of that, though I'm not sure if it is directly related to the loss of extrusion.

Here are other things I can try:

  • Replace Mosquito Magnum hot end
    • I have a regular Mosquito I ordered when the original problem looked to be caused by the hot end
  • Cold pull / disassemble the hot end again to make sure the current issue isn't new since the last time I did that a couple of days ago
  • Add extruder / stepper indicators on all of the involved stepper motors
    • Hopefully help determine whether the filament advance steppers are turning and whether the MMU2 idler is in the correct position to engage the selected firmware

Any other ideas as to what could be going on here?  I don't even know if the issue is caused by (partial?) clogging in the hot end or an issue in the filament path (mismatched feed rates, friction, ...).

This topic was modified 8 months ago by esb
Posted : 21/01/2022 8:37 pm
Active Member
Topic starter answered:
RE: Intermittent loss of extrusion during print

I should add that the printer prints very well with the MMU2 disconnected, though I haven't tried MMU2 - single filament prints in quite a while.  Additionally, filament movement while only the MMU2 is controlling it is very smooth and completely without grinding.  Its only when the filament is being moved by both the MMU2 and extruder that any grinding occurs.

Posted : 21/01/2022 9:28 pm