Hemera & moire

Discussion in 'Troubleshooting' started by Geoffray Doignon, Feb 20, 2020.

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  1. Geoffray Doignon

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    Hi all,

    So, I've pretty much tried everything I could think of and I am still getting moire on the surface of my prints (see picture). So far I've tried tuning the extruder stepper driver current, tried different filaments, different combo speed/acceleration/jerk, flow, stealtchop and spreadcycle, tl_smoother ... Always getting the very same pattern in all directions. Before switching I had an E3D v6 and BMG and that was ok. So I'm coming to the conclusion this is the Hemera stepper that has an eccentric shaft. Anybody has any idea or has the same issue ?
    Below the second image is a tower where I changed the extruder stepper current 25mA at at time from 550 to 850mA.

    IMG_0805 2.jpg CC967E7C-1FA7-4014-B187-6A80F2F22E8D.JPG My config:
    • Modded Ender 3
    • Hemera
    • SKR 1.3 board with TMC2208
    • linear rails on X and Y
     
  2. Haytham Bennani

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    Try reducing idler tension. I found that helped quite a bit. And I have a feeling this is the cost of the higher precision in the machining of the Hemera and its ability to have tighter control on filament extrusion. Its just a hunch.
     
  3. Spoon Unit

    Spoon Unit Well-Known Member

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    Have you played with increasing microstepping?
     
  4. Marcus Mendenhall

    Marcus Mendenhall Active Member

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    It's an interesting point about a very deterministic feed. If it we slipping around very much at all, you might never see this. It's very subtle, and wouldn't be visible without being extremely regular. The double drive gears on the Hemera are very toothy, and don't slip. Loosening it up, per Haytham's suggestion, might work. I just tried to make mine slip, preparing to calibrate nonlinear extrusion. At 5 mm/s feed rate, it is only extruding 2% less than at low speed. That's a very impressive drive capability.
     
  5. Geoffray Doignon

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    Actually I think I've finally identified the root cause. I think this a tolerance issue with the gear E3D sent me to replace my first cracked one. I've made a video to show the problem. The shaft is unbalanced and wobbling which in turn is probably creating this problem. I will have to contact E3D to ask for their opinion. I could easily insert my first 'cracked' gear and it rotated perfectly, the new one is hard to insert and wobbly.

     
  6. Haytham Bennani

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    That's an interesting issue. Please do keep the thread updated when you get to the bottom of this! :)
     
  7. SchmartMaker

    SchmartMaker Active Member

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    @Geoffray Doignon I've been battling these artifacts as well. Definitely extruder related.

    Like you, I tried about everything, including but not limited to checking PSU stability, trying new stepper cables, oiling the Hemera gears with differential 15k oil, elaborate Trinamic driver tuning, etc. Nothing worked or made a significant difference.

    Two suspects remain in my case; potentially unbalanced coils in the Hemera stepper or the Hemera gear assembly. I'm working on some calculations to be able to determine if my pattern is related to electrical or mechanical revolutions.

    Note that E3D already reported that a small number of stepper motors were sent out with a bearing pocket that was CNCed too close to the small gear.

    Does your wobble period constitute of a full revolution of the small or the big gear? I can't really tell from your video, the gears are turning pretty fast.
     
  8. Haytham Bennani

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    On a possibly related note, are you guys noticing "ripples" on the top surface of extruded material? I see it quite a lot with black PLA or any PETG (the glossier, the more visible). If you look at the surface of a perimeter being extruded (the top surface, not the sides), you may see "notches" or "ripples" that are less than 0.01mm (according to my Mito caliper), but they are consistently there. They don't change in spacing with print speed, and I'm practically sure this is the Hobb teeth pattern being reflected into the plastic (measurements seem to line up around 1.57mm). I'm reasonably sure this is due to how precise the gearing is on the Hemera, and is an artifact left by gear meshing (or backlash?) that would be totally normal in this setup.

    Due to the close tolerances E3D strives for in the Hemera, I'm sure we are all experiencing artifacts that weren't visible when we used to use less precise extruders..
     
  9. SchmartMaker

    SchmartMaker Active Member

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    Yes, I guess it would be theoretically possible to see these fine impressions return in the extrudate as well. Though I'd expect that effect to diminish with higher printing temperatures.

    If the pattern changes when printing wider and higher (e.g. with a 0.4 nozzle at 0.6mm width and/or 0.28 layer height) then you can be reasonably sure it's extruder related and not for example resonance or non-uniform stepping from the X or Y axis steppers.

    I'm printing in black glossy PETG to see and emphasize these issues.
     
  10. Wes Cherry

    Wes Cherry Member

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    I see very similar microripple with the Hemera. I have 3 hemeras and all reproduce the problem. It happens on my crossed gantry printer and delta. Some sample prints are here:



    The microripple changes with the extruder microsteps and with interpolation.

    I suspect the issue is resonance from the 1.8 deg stepper and a very tight constrained filament path that doesn't absorb those vibrations. A 0.9 degree stepper would probably lessen these effects.

    A friend with an Ender3 also sees similar effects, so it's almost certainly not the printer.
     
  11. Haytham Bennani

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    Unfortunately those links aren't loading.
     
  12. Wes Cherry

    Wes Cherry Member

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    Do they load if you click on the squares in the preview?. E3D server kept rejecting any jpeg i tried direct uploading. trying again. Yep. "There was an error with your file." happens with every .jpg I try. So I put imgur link which doesn't preview properly.

    https: //imgur.com/a/ysqdj9h

    copy and paste that URL, remove the space after the :
     
  13. Haytham Bennani

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    Yup that's what I was talking about. If you look at pictures of 3D prints online made with precise motion systems (like a TC, a Railcore, or a Jubilee), you'll start seeing them there too. :) Its not something limited to Hemeras at all.
     
  14. The_Slunk

    The_Slunk Member

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    I've done extensive testing with the extruder microstepping and current, and the only setting that is not causing ripples on my hemera (using the SKR mini E3 with tmc2209's) is 1/8 microstepping. Stealthchop vs spreadcycle seems to be making no difference. Running it with a 24v power supply at 840ma Vrms (per the motors rated current).

     
    #14 The_Slunk, May 5, 2020
    Last edited: May 6, 2020
  15. Haytham Bennani

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    Hmm interesting. I had tried that before on a Duet2 (TMC5160) and the problem persisted. Maybe I'll try again with quarter settings and see if that does anything..
     
  16. The_Slunk

    The_Slunk Member

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    Here are my results

    https://imgur. com/a/rPM7A3L
     
  17. Haytham Bennani

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    From those (nice) results, seems like we need to tune TMC stepper chop registers for the Hemera extruder motor. Should be able to help solve this issue. Now if only I knew how to tune them properly..
     
  18. The_Slunk

    The_Slunk Member

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    Yeah that's gonna take someone much smarter than me to figure out. I thought it was interesting though, that the deviation from 1/8 microstepping (going to to 1/4 or 1/16) seemed to show almost identical ripples. That's what got me interested in seeing if the current setting had any affect and it did not seem to.
     
  19. Haytham Bennani

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    So what I've found to reduce these artifacts the most has been to increase my jerk settings. I had a unique scenario where I was printing at 100mm/s or more, and had my instantaneous speed change set to 300mm/min in XY (that's jerk in Marlin), mainly to address some cornering issues with the mass of the Hemera. Bumped that up to 1200mm/min at those speeds, and most of my issues have disappeared. It was mainly caused by the slow jerk speed forcing the Duet to print out each small segment of curved sections too slowly. There's still some other odd artifacts that I suspect are from stepper driver pulses, but that's an entirely different matter.

    So just worth checking out for all those out there still trying to figure this out. This solution might not work for you, but it has solved 90% of the cases I was having.
     
  20. Pascal

    Pascal Member

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    Hi together I have exat the same problem and just can not get ahead. Has anything been found to solve this problem?
     

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