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Under Extrusion on Mk2.5 Kit  

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jayme.c
(@jayme-c)
Active Member
Under Extrusion on Mk2.5 Kit

Hi,

I've not had any luck printing anything taller than about 1mm with either PET, PETG or PLA since upgrading to the Mk2.5 kit a few weeks ago. Calibration is sound, and the first layer adhesion is usually solid. Every 0.8 to 1.4mm of Z the filament sensor would trip and detect a need for a new filament to be loaded despite there being plenty available. I'd go through the process or unloading and loading and off goes the print.

After reading about some issues with the filament sensor, I turned turning that off. A few trial prints suggest that the sensor was working close to perfectly after all, as the filament wasn't being extruded successfully. Despite heat changes and slowing the print to 50% with PET or PETG, the hotend stopped spewing goodness and went dry regularly.

Have checked the hobbed gear alignments, heat options and various slow print speeds. All with no luck. The filament is just not being passed to the hotend with enough volume. When it works, it's perfect! But then it runs out of juice. The result as prints that start well and degrate to classic under-extrusion in strata of about 1mm. When iI pull the filament, you can clearly see that the length of filament in the extruder is about 15mm too short to fill the tube and the leading end is a series of stringy, melted hairs rather than a normal melted solid.

All ears for anyone with some ideas?

Images: https://photos.app.goo.gl/cUSZ1cAh3vP4CMrS2

Jayme

Posted : 01/06/2018 12:12 am
Guardian_DE
(@guardian_de)
Eminent Member
Re: Under Extrusion on Mk2.5 Kit

I had the same problem and I'm not sure how I came over it, but in the end it worked.

Even though you mentioned you already did, double check the tension of the springs for the hobbed gears. I had to loosen it significantly. This was definitely part of problems. In case this is also part of your problems you should hear the clicking sound of the skipping extruder.

Did you check for clogs of your hotend? Even though I did not have a full clog, I cleaned the nozzle with a acupuncture needle and I think it also helped.

Maybe your nozzle is too low and it gets partly clogged because the filament can not get out of the nozzle because the nozzle is too low.

Posted : 01/06/2018 9:01 pm
jayme.c
(@jayme-c)
Active Member
Topic starter answered:
Re: Under Extrusion on Mk2.5 Kit

Thanks for these suggestions. I'll try the needle trick just to be sure.

The suggestion about having the nozzle too low is interesting. I've had some challenges getting the hot filament to sit with the right level of squish. Will try fiddling with that some more, too.

Have had no real intuitive sense of how tight the sprung extrusion screws should be set. Unlike the Mk2, you really can't adjust them on the fly anymore.

Posted : 01/06/2018 11:39 pm
Guardian_DE
(@guardian_de)
Eminent Member
Re: Under Extrusion on Mk2.5 Kit


Have had no real intuitive sense of how tight the sprung extrusion screws should be set. Unlike the Mk2, you really can't adjust them on the fly anymore.

The manual depicts a good initial setting for the spring screws. My screw heads stand out about 1 mm from the extruder case. And I don't have any problems with adjusting them on the fly. Where's your issue with that?

Posted : 02/06/2018 1:17 pm
jayme.c
(@jayme-c)
Active Member
Topic starter answered:
Re: Under Extrusion on Mk2.5 Kit

I'm very glad for you.
As I said, it's a lack of feel for the new system.

Posted : 02/06/2018 4:58 pm
tom.b6
(@tom-b6)
Trusted Member
Re: Under Extrusion on Mk2.5 Kit

Here's what I find works for setting the extruder tension screws.
1) Remove filament
2) Loosen the screws
3) Tighten the screws until they barely contact the springs (you can feel this), then maybe another slight bit more (1/8 turn?).
4) Load the filament.

Having the screws flush, as indicated in the manual, is far too tight. I had terrible noises until I loosened them.

Posted : 05/06/2018 12:28 am
jayme.c
(@jayme-c)
Active Member
Topic starter answered:
Re: Under Extrusion on Mk2.5 Kit

Thank you! That's very much appreciated. I'll follow your suggestions.

Posted : 05/06/2018 2:38 am
digibluh
(@digibluh)
Reputable Member
Re: Under Extrusion on Mk2.5 Kit

sensor doesn't detect jams, only if it's present. super shiny black filament could be an issue. i've printed 12+ hours with some shiny black without issue though.. so it "depends".

Nozzle clog or potential PTFE tube issue , gear tension issue... also make sure gears are both aligned to each other.

Posted : 05/06/2018 6:53 am
jayme.c
(@jayme-c)
Active Member
Topic starter answered:
Re: Under Extrusion on Mk2.5 Kit

Thanks for that clarification. Was under the impression that the sensor also tries to detect when the filament wasn't advancing. It certainly kept claiming that it needed afresh load. That happened with about the same frequency as the filament failed to advance fast enough.

Posted : 05/06/2018 1:27 pm
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