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Cyclic under-extrusion making patterns on first layer  

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RetroModder
(@retromodder)
Active Member
Cyclic under-extrusion making patterns on first layer

Mini has started to make this weird pattern due to under-extrusion of the first layer.

Some prints come out perfect, such as XYZ or 4mm-nozzle calibration cubes. I also test printed two large single-layer circles, one with a rectilinear pattern, and the other with a concentric for a long constant run of filament extrusion; they both came out perfect. It seems like any "back-and-forth" in the X and Y directions is causing this, but I'm not sure why.

Setup:

  • PLA, 4mm nozzle
  • 215C first layer, 210C other layers, 60C bed
  • Bondtech extruder and heatbreak installed and were working well before
  • 0.2mm layer height set to SPEED mode

 

Things I've tried:

  • Rebuilt the Bondtech extruder, cleaned out loose pieces of filament and brushed drive gear
  • Generic grey PLA shown, also tried black Prusament
Posted : 08/07/2022 1:44 am
RetroModder
(@retromodder)
Active Member
Topic starter answered:
RE: Cyclic under-extrusion making patterns on first layer

When I move the Z-offset closer to the bed, this just "shifts" the problem down and areas that look underextruded now look fine, but the areas that were previously fine now have dragging and over-extrusion from smushing.

 

Posted : 08/07/2022 2:28 am
Lillalysmasken3
(@lillalysmasken3)
Active Member
RE: Cyclic under-extrusion making patterns on first layer

I had some serious issues with inconsistent extrusion. Most likely to do with bondtech heat break.
Check this thread.
https://forum.prusa3d.com/forum/user-mods-octoprint-enclosures-nozzles/strange-extrusion-problem-using-bondtech-extruder-and-heat-break-on-prusa-mini/
Unfortunatly the only thing that really helped was changing the hot end to Dragon from Phaetus, but now it prints like it was supposed to.

Posted : 08/07/2022 7:51 am
RetroModder
(@retromodder)
Active Member
Topic starter answered:
RE: Cyclic under-extrusion making patterns on first layer

Still chugging through this thread but for how many good things I heard about the bondtech heatbreak before purchasing, it's confusing to see people have issues with it and going back to the stock one. Will try this later, thanks for the link!

Posted : 08/07/2022 3:34 pm
fuchsr
(@fuchsr)
Famed Member
RE: Cyclic under-extrusion making patterns on first layer

I don't have a Bondtech heat break but my perspective on this is, don't "upgrade" just because you've read about it. Upgrade for a reason. Prusa wouldn't ship thousands of their machines to good reviews if their heat break was trash. 

Posted : 09/07/2022 6:03 am
Razor liked
RetroModder
(@retromodder)
Active Member
Topic starter answered:
RE: Cyclic under-extrusion making patterns on first layer
Posted by: @fuchsr

I don't have a Bondtech heat break but my perspective on this is, don't "upgrade" just because you've read about it. Upgrade for a reason. Prusa wouldn't ship thousands of their machines to good reviews if their heat break was trash. 

I upgraded because I had issues with the Prusa heatbreak, experiencing the shrinking PTFE tube that many have also seen after owning the printer for any substantial time. And so I read up on good things about the Bondtech heatbreak but just recently learned about the bad. I'll continue to follow that other post.

Posted : 09/07/2022 7:51 pm
fuchsr
(@fuchsr)
Famed Member
RE: Cyclic under-extrusion making patterns on first layer

Fair enough - sorry, it wasn't obvious to me from the original post. 

If it was a heat break issue, I wouldn't expect a peculiarly periodic pattern like this. It's also confusing that the circular test prints you mentioned didn't show it. I would probably recheck the x and y axis belts and pulleys and the motor axle grub screws as the next step of trouble shooting. 

Posted : 09/07/2022 8:34 pm
RetroModder
(@retromodder)
Active Member
Topic starter answered:
RE:
Posted by: @fuchsr

Fair enough - sorry, it wasn't obvious to me from the original post. 

If it was a heat break issue, I wouldn't expect a peculiarly periodic pattern like this. It's also confusing that the circular test prints you mentioned didn't show it. I would probably recheck the x and y axis belts and pulleys and the motor axle grub screws as the next step of trouble shooting. 

All good. I actually did end up swapping back to the stock heatbreak this weekend and that seemed to completely fix the problem. I forgot to also mention that I believe I checked all the belts and set screws when the issue first showed up. I'm still not 100% sure if the issue was in the heatbreak itself, or just having a newly assembled hotend was the trick (ensuring tightness in all of the fittings, new thermal paste, etc). However, I didn't find any assembly issues when I disassembled the Bondtech heatbreak setup.

Like you said it's strange that this symptom was the result of an issue in the hotend, I thought for sure it was something mechanical. Especially since I didn't have any oscillations in the nozzle temperature.

Posted : 11/07/2022 3:55 pm
sandysasmita
(@sandysasmita)
Trusted Member
RE: Cyclic under-extrusion making patterns on first layer

I have this issue before and find out that my extruder gear is dirty, so when it turns at some point (when the dirty side touch the filament) the gear slip and cannot grab/push the filament properly and have this underextrusion issue.

Posted : 13/07/2022 2:17 pm
RetroModder
(@retromodder)
Active Member
Topic starter answered:
RE: Cyclic under-extrusion making patterns on first layer
Posted by: @sandysasmita

I have this issue before and find out that my extruder gear is dirty, so when it turns at some point (when the dirty side touch the filament) the gear slip and cannot grab/push the filament properly and have this underextrusion issue.

That's what I thought it was at first, so I rebuilt the extruder and didn't find much wrong with it. I think the amount of plastic buildup in the drive gear seemed normal, so after brushing it out I put it back together and the problem still persisted.

Posted : 13/07/2022 2:27 pm
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