Suddenly no filament anymore  

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Jiheffe
(@jiheffe)
Eminent Member

Prusa i3 Mk3s with stock extruder and Dragon hotend.

After an overnight PETG print on the textured sheet, I switched to a smooth sheet and loaded PLA. Loading went perfect, thev new filament came out of the nozzle as usual. But when actually printing,  no filament gets extruded, not even the purging strip in the front left of the plate... The extruder motor is turning, though...

Tried different filaments (PLA, PETG) on both smooth and textured sheets, did systematically cold pulls in between... Up to some moment when a cold pull would not work anymore, nozzle completely clogged... Removed the nozzle, passed a filament trough the complete assembly to check nothing was in the way, and replaced clogged nozzle by a new one...

Still the same. The filament passes without problem when loading, but when printing nothing gets extruded, not even the purging strip... The extruder moter is turning.

Any idea what's happening?

Best Answer by Jiheffe:

Solved 😎
While dismantling the extruder to remove the Dragon hotend, I found this little guy
...

Together with its twin, it secures the top part of the hotend to the heatsink. It had fallen out and the other one was loose as well... Secured both screws and now al is up and running again.


Still trying to understand why filament was moving normally trough it when unloading/loading or during cold pulls, but not when printing...

Posted : 06/08/2020 3:43 pm
bobstro
(@bobstro)
Illustrious Member

Some of this is no doubt repetitive for you, but hopefully useful...

I always do cold pulls at temps elevated well above whatever materials I've printed with. This is particularly important when going from higher-temp (PETG) to lower temp (PLA) as any stuck filament will cause jams. For this reason, I like to use cleaning filament. eSun works very well. The beauty of the cleaning filament is that it is very sticky (good for catching debris) and will also extrude at a very wide range of temps. If any does get left over in the hotend after a pull, it will melt out at PLA temps. The key is that the cleaning filament will can be used a temps higher than anything I've printed to ensure anything inside melts, as well as at lower temps to avoid contributing to clogs. The procedure I use is:

  1. Unload PETG.
  2. Raise nozzle temp to 265C.
  3. Run cleaning filament through until it runs clear.
  4. Zero temps.
  5. Open extruder door.
  6. When nozzle is cooled, set print temp.
  7. At around 70C, start pulling up firmly and steadily. At 90-110C, a plug will pop out.

I try to do this on every nozzle change and when going from high to low temp filaments. Some folks like to jam more cleaning filament in as it cools in step 3, manually feeding it in (with extruder open) until no more can be pushed through the cooling nozzle.

This post was modified 2 months ago by bobstro
My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 06/08/2020 5:21 pm
Jiheffe liked
Jiheffe
(@jiheffe)
Eminent Member

Solved 😎
While dismantling the extruder to remove the Dragon hotend, I found this little guy
...

Together with its twin, it secures the top part of the hotend to the heatsink. It had fallen out and the other one was loose as well... Secured both screws and now al is up and running again.


Still trying to understand why filament was moving normally trough it when unloading/loading or during cold pulls, but not when printing...

Posted : 06/08/2020 6:54 pm
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