Printer refuses to do a certain print



  • Can anyone print this with a CoreXY Bowden (~50cm) at all? https://www.thingiverse.com/thing:2932267

    My printer prints the base just fine, but then outright refuses / clogs itself up as soon as the fine outer details start (the part roughly above 2cm Z). There's nothing specific to show in the pictures other than loads of inconsistent extrusion. It keeps blobbing or underextruding a lot and eventually clogs. I'm suspicious that my Bowden just has too much backlash. It would help, if anyone with a Bowden and CoreXY could try printing that part and share his settings.

    I would like to not dilute this with my settings as they are obviously plain completely wrong for this print.

    In addition to all the print parameters like resolution, speed, acceleration, jerk, temp etc, I've also tried different slicers like older Slic3rPE, newer Slic3rPE, older Cura, Slic3r, Simplify3D. It appears to be not dependant on the GCode generated, but just something I'm missing on the printer.

    It would really help if anyone would try it, then post a picture and settings for it. My printer usually clogs somewhere at 2-6cm Z. At this point it's unclear whether it's the Bowden backlash or generally the Bowden. If nobody can print this, then it's time to switch to direct drive...



  • You should try running a retraction test or "torture test" with your printer.
    Bowdens have an inherent design flaw that makes them less capable printing such things by default.
    They need very well tuned retraction length/speed values to work with this.
    If you use too much retraction, it pulls the filament up too far into the heatbreak, molten filament solidifies and it clogs.



  • @NitroFreak do you have a test you recommended?


  • administrators

    Please post your config.g file, we may be able to spot a problem.

    What hot end are you using, what retraction parameters, and what pressure advance setting (if any)?


  • Moderator

    @Baenwort said in Printer refuses to do a certain print:

    @NitroFreak do you have a test you recommended?

    The linked model looks like a pretty good retraction test as it is. Though not a test print obviously.

    Something like this would be much quicker. retraction_test_v1-0.stl



  • @Phaedrux @dc42 @NitroFreak
    E3D Volcano, 1.75mm, 50cm Bowden, 0.4 but now 0.6 nozzle

    I changed the nozzle to a brand new brass 0.6mm to rule it out. I did a test print of the retraction_test_v1-0.stl and now I'm more puzzled than before.

    5a1a6ede-4dfe-4fea-b9f0-b8ae31cbae5b-image.png

    That blobbing on the first layers is where PA was set to 0.6. I disabled it during print and this problem went away. Maybe the value is high, but what's there to prevent over-/underextrusion with a lower value? I'm afraid we're slowly drifting away from land on ice again... In any case, I print without PA from now on, as the 0.6 brass nozzle behaves much better than the old hardened steel 0.4.

    Apart from stringing, there's not much to report. I did 6 retraction test prints with varying temps, layer height, retraction settings and they are all nearly identical. I do not expect stringing to ever improve unless I change the mechanics, because there is quite a bit of backlash on the Bowden and it's a Volcano with 0.6 nozzle. It's acceptable, as I usually don't do fine icicle prints.

    I'll try that skeleton planter print again and, if it doesn't work, I'll post all settings.



  • @Phaedrux @dc42 @NitroFreak

    Did another print of skeleton planter after taking care of excessive backlash in the Bowden. Printer managed to print the fine outer features without major issues without PA. During the print I typed M572 D0:1 S0.05 and it started ramming the filament directly after changing. After M572 D0:1 S0 printer was back to normal.

    config_10.06.2020.g

    GCode: https://drive.google.com/file/d/1FKtLUgamtOzPcgjB_Lw4hD6HeXsJvDfk/view?usp=sharing

    I set the Speed to 35% in DWC at the beginning of the print.

    I also tried changing temperatures from 200 to 185 in 5 degree increments and observed no difference.


  • Moderator

    Have you tested using PA without the extra stepper parameters (B, F, Y) in M569?

    M569 P8 S0 B0 F6 Y0:14:0



  • Its thermal. The jamming is at least.

    Basically for any hotend you need the thermal transition to as close to the melt chamber as possible. When the extruder retracts its pulling hot material higher in the thermal break and moving the thermal transition higher up. If you retract too many times in a given time period, the thermal transition moves too high up, friction increases, extruder jams.

    Cura specifically has a setting that limits the number of retractions in a given distance (which works, even though it should be about duty cycle).

    You just happen to be printing a part with far more need for retraction. Try printing with no retraction, I would expect that the extruder doesn't jam.

    Bowden is only more prone to this as the inherent backlash/elasticity needs much longer retraction distances, so its easier to overdo the retraction distance.
    The fact that people generally are pairing bowden drive with tiny extruders doesn't help though, the smaller the heatsink, the less capacity it will have for this kind of thermal creep.

    Try using Cura's setting, it's under 'Travel', you want to play with 'Maximum retraction count' and 'Minimum extrusion distance window'. Those will effectively limit the duty cycle, so your extruder isn't spending all its time retracting.

    Another trick is to just slow down the print.

    As for stringing? A Volcano with 0.6 nozzle? Yeah, you can't stop it, the melt chamber is huge, that thing is going to dribble like mad. But when printing at relatively low speeds with a high-flow hot-end like that, the dwell time is so long you can extrude at much much lower temps than you might expect.
    Try going down below 185C, till it just jams, you might be surprised.



  • @Phaedrux Extruder motors are not affected by M569 B, F, Y, as the second part is commented out.

    @theruttmeister I'm past this phase of troubleshooting. I was printing at basically 20-30mm/s. The hotend is rammed so hard that the molten plastic is flowing upwards, I'm sure of it.

    Also, a low value of S0.05 should not cause so much extrusion.

    Please, someone follow my request and try print this on a CoreXY Bowden.


Log in to reply