UNSOLVED Bad Inconsistent Extrusion



  • Hello, I recently finished building my second printer and I'm experiencing terribly inconsistent extrusion. I've been trying tips on fixing bowden extrusion issues but so far no luck.

    IMG_5605.JPG

    The printer will alternate between under extrusion to massive over extrusion from layer to layer on small features. But is also pretty bad in general. I also sliced the same retraction test above in PrusaSlicer with the mini profile and matching jerk, acceleration, speed settings and it was about the same. It will be string free until the first blob forms then its terrible.

    IMG_5614.JPG

    IMG_5615.JPG

    As a sanity check I also did a vase mode print to check if the hotend couldn't keep up. Other than cooling issues it was fine up to 90mm/s which is much faster than I'm printing at the moment.

    Printer Details:
    CoreXY with a bondtech bmg, ~400mm E3D bowden tube, and a E3D threaded heatsink V6 setup

    Troubleshooting So Far:

    • Pressure advance (high and low)
    • XYZE Jerk/ acceleration/ speed (high and low)
    • Checked bowden system for excess resistance
    • Cleaned and adjusted bmg gear spacing
    • Different bowden collet clip thicknesses
    • Different E microsteps and current
    • Different coast and retraction settings
    • Hotend and bed temperatures don't vary much

    One odd thing is that even with coasting, alternating layers will flow a bunch of material as it prints the last part of the layer.

    I'm at a loss and would appreciate any help.


  • Moderator

    Post your config.g and maybe your slicer settings or a sliced gcode.

    HAve you PID tuned the heaters? Are you using the right thermistor values?



  • Config: config.g

    Test using modified mini gcode: 8MMCYL_0.2mm_PLA_MINI_15m.gcode

    Test from Cura: CYLT6.gcode

    Heaters are PID tuned. I'm not confident about the thermistor values. The bed uses a keenovo heater with built in 100k and the hotend is standard E3D parts.

    Should the E3D thermistor be changed to these (T100000 B4725 C7.06e-8) and the bed stay with the default settings?



  • The file import tool didn't like the cura profile file type so I changed it to .txt

    DOZER_PLA.txt

    I varied coasting and pressure advance for different tests but the base profile is with no coasting.



  • As an additional odd note:
    When I first installed the bondtech extruder the main gear turned with different amounts of backlash. Rotating it by hand it would tighten up slightly during part of its rotation then loosen and have a bit of backlash during other parts of its rotation. To see if it was a pinion gear spacing issue I tried moving the pinion further away from the stepper motor face but it didn't change. I also checked the bearings throughout but they were in good shape.


  • Moderator

    @JPH said in Bad Inconsistent Extrusion:

    Should the E3D thermistor be changed to these (T100000 B4725 C7.06e-8) and the bed stay with the default settings?

    Yes. If you have the E3D thermistor you should update the settings, otherwise your temps will be off, which could explain some of the over extrusion/leaking.


  • Moderator

    M350 E8 I0 ; test seperate extruder settings

    I'd definitely stick to x16 with interpolation on the Extruder. Dropping or raising microstepping rarely solve anything.


  • Moderator

    M82 ; use absolute distances for extrusion

    Looks like you have your slicer set to absolute extrusion. Try setting it to relative extrusion. I don't think it will have an effect on your problem, but it's still the better way to go.

    Also, have you calibrated the extruder?

    https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+Maestro+Guide+Part+4:+Calibration/40#s165



  • @Phaedrux Thank you for saving the day 😊

    I went ahead and did everything you recommended, ran a new PID tune, and re-calibrated my extruder at the lower recommended feed rate.

    The difference is night and day. I'm still getting some issues where Cura has dropped the feed for cooling but it is a massive improvement.

    IMG_5634.JPG

    I bumped the minimum speed up from 10 to 20mm/s and that seemed to be the final tipping point. I'm not sure why that would make such a large difference though, unless its just preventing Cura from throttling the extrusion speed?

    IMG_5638.JPG

    I might check later if changing firmware compatibility and gcode flavor to reprap would change Cura's behavior at those low speeds.



  • @Phaedrux said in Bad Inconsistent Extrusion:

    M82 ; use absolute distances for extrusion

    Looks like you have your slicer set to absolute extrusion. Try setting it to relative extrusion. I don't think it will have an effect on your problem, but it's still the better way to go.

    Curious ... Cura allows to select relative extrusion but it also says that no matter of the setting, the gcode output is always absolute.
    Apparently the slicer has an easier time working with the relative extrusion hence the ability to select the option.

    Thoughts ?


  • Moderator

    @jens55 Anytime Cura does something weird the answer is usually because Ultimaker.



  • Let me change my question a bit:
    Assuming I use Cura as a slicer, should I select 'relative extrusion' in Cura?
    Should I set M82 in config.g ?
    Should I do anything else ?


  • Moderator

    @jens55 I use cura and I set relative extrusion. I also have M83 in config.g. I assume you mean M83, because M82 is absolute. Also, even if you have M82 in config.g if you have cura set to relative, it will insert M83 into the gcode at the start anyway.

    I don't think there is anything else to do.



  • Thanks !


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