uneven surface finish



  • Hi,
    I have a delta and im am getting uneven surface finish, I have tried all types of microstepping from 16 to 128 and currents from 800mA up to 2000mA.
    I am using wantai 57bygh420 with 20 tooth pulley on original hiwin rails and 13:1 ratio geared extruder with original E3D volcano 0.8mm nozzle (temps are within 0.3°C) smaller nozzle gives worst result.
    Layer fan ON or OFF gives same results
    Magnetic arms
    Tightening the belts makes the uneven surface more visible
    Tough it was the belt touching the idler pulley housing but it wasn't
    Can't understand if this is extrusion or kinematic related problem
    The Arms are 1100mm so the system is not very stiff but it has no play and I am printing at 30/40 mm/s

    Any advice?
    1_1531394402665_IMG_20180712_1314235.jpg 0_1531394402664_IMG_20180712_1314144.jpg

    
    M92 X80 Y80 Z80 E1166			; set axis steps/mm
    M350 X128 Y128 Z128 I0			; set XYZ microstepping I1= interpolated I0= not interpolated
    M350 E64 I0				; set extruder microstepping
    ;
    M566 X3000 Y3000 Z3000 E1200                                            ; Jerk: Set maximum instantaneous speed changes (mm/min) (E was 1200)
    M203 X5000 Y5000 Z5000 E1200                                            ; Set maximum speeds (mm/min) (E was 1200)
    M201 X250 Y250 Z250 E500                                                ; Set accelerations (mm/s^2)(was 5000)
    ;
    M906 X1500 Y1500 Z1500 E400 I40                                            ; Set motor currents (mA) and motor idle factor in per cent
    M84 S30                                                                 ; Set idle timeout
    


  • Have you compared the target extrusion thickness to actual? Backing off on the extrusion multiplier helped me get better vertical walls recently.



  • @doctrucker
    photos are currently with extrusion set to 90%
    steps /mm are correct so I don't want to go more than 10% off, which is a lot



  • I made a test with 1mm nozzle, extrusion multiplier 70%, extrusion width 0.7, layer height 0.5, outline speed 20 mm/s
    this is the result...so strange
    1_1531434384669_IMG_20180713_0020101.jpg 0_1531434384668_IMG_20180713_0020041.jpg



  • I have had the same uneven finish from my coreXY printer as pictured in your first post when using volcano with 0.8 mm nozzle. I tried everything I could think of to ferret out the source and could not. If you look at the corners under a microscope, they appear to stack up just fine, so it isn't the precision of the mechanism. I suspect it's the behavior of the cooling plastic. What I think is happening is that as the previously deposited layers of plastic cool and shrink, they distort the wall slightly and cause the new line to land a bit off-center on the previous line. The long straight vertical wall is the worst case scenario. If you print a cone, the effect almost disappears. I suspect the curvature resists the warping force created by the shrinking, cooling plastic better than a straight wall does, so the layers have a chance to stack up properly.

    When you start printing other things with that nozzle, you'll find gaps at the start/end of layers/lines, especially after travel moves. With a lot of messing around, you can tune them out for a specific part being printed, but as soon as you try to print multiple parts on the bed, or even a different part, all bets are off. With a 0.4 mm nozzle, the gaps are controllable/nonexistent, with a 0.6 mm nozzle they are starting to become a problem, with a 0.8mm nozzle they are severe. There is a plug-in for Cura called "scalable extra prime" that varies the extra extrusion upon unretract as a function of the travel distance. It helps, but is not a cure for the gaps.

    The second photo isn't strange at all. You're trying to print a line that is thinner than the nozzle diameter. That's what happens when you do that- you're under extruding. It's like the water coming out of a slow running faucet- if there's some distance to the sink, the stream pulls itself into discrete droplets. In this case, the droplets form before the plastic cools enough to stiffen. I'm pretty sure that's a result of surface tension, just like the formation of water droplets.


 

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