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Inconsistent extrusion  

Eminent Member
Inconsistent extrusion

I'm having trouble with inconsistent extrusion on my Mini. Sometimes it prints perfectly after a filament change or a cold-pull, but after a little while it extrusion starts to vary. From so low there is small holes in a line to blobs hanging on the side of the print.

I have done a lot to get rid of this:

  • Installed a Bondtech extruder (updated e-steps, and verified them).
  • Installed Bondtech heatbreak and did a PID autotune. Temperature is steady.
  • It happens with multiple filaments. The two in the picture are just-out-of-the-box Prusament Jet Black and Mystic Brown.
  • Print temperature has no effect on this problem.
  • Changed the nozzle to a new one.
  • Cleaned the nozzle with an acupuncture needle.
  • Changed the bowden tube to a new one.
  • Changed the PTFE in the hotend. Both when installing the bondtech heatbreak and again later. No debris or any leftovers to be seen there.
  • Reset the heatbreak to put more compression on the PTFE tube even though that shouldn't be ad critical with the bondtech heatbreak.
  • The extruder stepper is not warm nor does it click or grind the filament.
  • I've printed both from usb and from Octoprint.
  • Tightened the belts. May have been a bit loose, but it didn't help.
  • Tried tightening and loosening the tension on the extruder with no effect.

The prints in the image is simple vase printed squares. 

What else can cause this effect?

Posted : 24/11/2020 4:08 pm
New Member
RE: Inconsistent extrusion

Sorry I don't have much to contribute here as you did a lot of troubleshooting already. 
Did you reach out to Prusa support btw? 

I'm following these threads as I'm on the fence about ordering the MINI (or the new MINI+).

Posted : 25/11/2020 12:05 pm
Eminent Member
Topic starter answered:
RE: Inconsistent extrusion


That's the next step.

Posted : 25/11/2020 1:54 pm
New Member
RE: Inconsistent extrusion

It looks a bit like layer shifting, but on some layer it looks like its squeezed. Whats the tempreture you're printing with? Did you tried to change it?

Does this also happen at other prints?

Posted : 04/12/2020 3:41 pm
Peter Susán
Eminent Member
RE: Inconsistent extrusion

I have the same issue with my Mini. If I clean up the hotend with a cold pull, the first print seems like ok, then it over/underextrudes again. I also have the bondtech extruder and the heatbreak, also upgraded the PINDA probe to the Super PINDA. I'm really clueless right now.

Did a cleaning, still there is a bit of overextrusion 

The next one totally failed...

After a cold pull, again, quite decent.


After this, of course it goes back to inconsistent again...

Posted : 21/12/2020 12:54 pm
Illustrious Member
RE: Inconsistent extrusion

I start from easy to hard and with human error first.

Check list for extrusion issues:

  1. Maker sure your slicer settings are correct.
  2. Is it the filament?  PETG will not print with PLA settins and bad filament is always a possibility.  
  3. If it starts ob the first layer, check your live Z - too close will hinder extrusion.  
  4. Check your idler screw.  
  5. Check your gears and hobbed pulley.
  6. Try a purge filament.  

If none of these work, do a cold pull and post it here.  


Chuck H
3D Printer Review Blog...
Posted : 21/12/2020 1:03 pm
Peter Susán
Eminent Member
RE: Inconsistent extrusion

Yeah, well. The slicer settings are fine. I'm purposely reverted everything back to default. My only modification is the custom gcode for the bondtech extruder and PID values for the heatbreak.

I'm only using PLA, Prusament Galaxy black to be precise, and using the prusa slicer profile for it.

The first layer is fine, it sticks, no problem with that

The idler screw for the bondtech is a bit different, but tried tight and loose settings besides the default 3-4 full turns for PLA. Gears are fine, no residue inside the extruder.

Unfortunately I don't have any cleaning filament, but already disassembled the hotend to pieces and cleaned it bit by bit. Everything is shiny and clean inside.

Digged out two recent cold pulls from the bin 🙂 If you would like, I can do a fresh one.

Posted : 21/12/2020 1:14 pm
Peter Susán
Eminent Member
RE: Inconsistent extrusion

There is another discussion with over/under extraction with the Bondtech upgrades, what turns out to be the same problem:


Posted : 26/12/2020 9:42 pm