Hemera E-stepper microstepping quality

Discussion in 'HotEnds & Extruders' started by kasom, Mar 9, 2020.

  1. kasom

    kasom Member

    Joined:
    Mar 9, 2020
    Messages:
    4
    Likes Received:
    0
    Background story: I bought E3D Hemera and wrongly set vref to 0.5v on the stock Ender 3 board. Skipped step severely. Increased vref to 0.7v, calibrated e-steps, etc. Got a rough surface on all sides. Slowing down didn’t help.

    I printed a cube in vase mode and got salmon skin on all sides. Try varying the print speed. The salmon skin pattern stays the same, but it’s much stronger when printed slower. What!! I always think that print slower = better result. I tried to print even slower, and noticed that the extruder pulled the filament in not smoothly. It seems like the extruder only moves on full or half steps.

    To verify this observation, I wrote a script to generate G-code that will align the extruder’s full step on every layer. I created a single wall octagon that each side has n * (mm per full step) long.

    The result confirms that the pattern aligns with the E-stepper’s full step. I can produce a perfect vertical salmon skin when setting the extruder step per mm equal to the setting in the printer’s firmware. A slanting salmon skin can also be produced when setting the extruder step per mm slightly different from the firmware’s setting.

    Correcting the vref to 0.96v helps a little. The pattern is still there. I’m waiting for SKR Mini E3 board. I’m still not sure if my Hemera has something wrong, or it is just the result of this particular combination with the Ender 3’s stock board.

    Here is my script: https://3dprinting.wheretogo.in.th/e-stepper.php


    This octagon was printed at 20,30,40,60,80 mm/s (bottom to top). The pattern is the same for all sides.

    89039273_2618645781590580_4585814484056014848_n.jpg

    Left: incorrect vref at 0.7v, Right: 0.96v

    89551060_547173215917237_5063664956201762816_n.jpg

    Using 394.87 step/mm (as set in firmware) the pattern width is 2.57mm. As calculated in the script.

    89692113_190453462259036_4922174023208534016_n.jpg

    slanting salmon skin. Set e-step per mm in script to 409, the firmware is set to 394.87.

    88426604_596349594248927_8437336710370557952_n.jpg
     
  2. Thorinair

    Thorinair Well-Known Member

    Joined:
    Aug 8, 2017
    Messages:
    50
    Likes Received:
    7
    This looks like ringing to me... The steps shouldn't be aligned like this. There are tiny bit of stepper artifacts there, but are hidden by all the extreme ringing. Push your accelerations down.
     
  3. kasom

    kasom Member

    Joined:
    Mar 9, 2020
    Messages:
    4
    Likes Received:
    0
    The bottom part printed at 20mm/s. Tomorrow I'll print slower & lower the acceleration, but I don't think that is the case.

    They align because I force the length on each side of the octagon to be multiple of extruder's full step.

    In the last photo I force the length of the octagon to be slightly different from the multiple of the extruder's full step to prove that the patten on each side is caused by the extruder's microstepping.
     
  4. kasom

    kasom Member

    Joined:
    Mar 9, 2020
    Messages:
    4
    Likes Received:
    0
    I have replaced the control board with SKR Mini E3. With the new board, the coarse pattern that aligned to the e-stepper's full step has gone. The fine pattern is still there, but it's much smoother than the old one when running my finger on it. Wall thickness is now spot on, it was 0.42 because of the rough texture on the surface.
    89533991_146150806636069_3783968674285617152_n.jpg

    At first I thought the fine pattern is due to microstepping so I expected (number of full step on each side) * (microstepping) = 10 * 16 = 160 teeth, or half of it = 10 * 8 = 80 teeth. But upon inspection, that is not the case. Printing faster also resulted in lesser number and less pronounced teeth.

    speed-skr.jpg fullsteps.jpg
     
  5. kasom

    kasom Member

    Joined:
    Mar 9, 2020
    Messages:
    4
    Likes Received:
    0
    Replaced X and Y motors with JK42HS34-1334A and 16 tooth pulleys.

    At 20mm/s, compared to the old motor/pulley combination, the fine pattern is more spaced out and the surface is smoother. At 15mm/s the frequency of the pattern is 2x of that at 20mm/s.

    motor-pulley.jpg

    Printing faster using opaque filament the fine pattern is not as noticeably as in the transparent filament. Ringing is more evident.

    ringing.jpg
    layer-height.jpg

    My conclusion is that the coarse pattern that align with the e-stepper's full step comes from the poor quality microstepping (solved by the TMC2209). The fine pattern might be the result from the combination of motor's torque, microstepping quality (again?) and the momentum of the moving hotend and heated bed. I've ordered some 0.9 degree motors, wonder if it can improve the result.
     
  6. Ikarisan

    Ikarisan New Member

    Joined:
    Jun 7, 2020
    Messages:
    1
    Likes Received:
    0
    Hi!
    Can you tell us any news? I am facing the same problem with my Hemera and my Duet3D Wifi board. The slower I print the stronger is the pattern. :(
     

    Attached Files:

  7. csaba

    csaba New Member

    Joined:
    Nov 24, 2020
    Messages:
    1
    Likes Received:
    0
    Let us know, pls if the 0.9 degree motor gonna solve this issue! I have the same problem, and this is making me MAD!
     
  8. archaon

    archaon New Member

    Joined:
    Dec 29, 2020
    Messages:
    1
    Likes Received:
    0
    I have the same problem with 0.9 degree motors. So this isn't the solution.
     

Share This Page