how to interpret these vertical bands?

Discussion in 'Calibration, Help, and Troubleshooting' started by R Design, May 12, 2016.

  1. R Design

    R Design Well-Known Member

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    We're looking at the light gray cylinder and the print is upside down (you see the slight flaring from a too tight 1st layer in the top left corner).

    It's a 2.5cm cylinder and was printed on a bed with other parts. The first 2/3 of the cylinder are printed nominally at top speed ( 50mm/s with no perimeter underspeed) and the last part of the print (the bottom of the image here) was slowed by S3d to, say, 5mm/s since by then this was the tallest part on the bed and it was trying to maintain a certain layer time.

    At "high speed" I'm wondering if those vertical bands are:

    a) "ringing" as the nozzle changes direction to follow the vertices of the STL mesh?

    b) some weirdness relating to 8bit electronics struggling with curves at speed: http://forum.e3d-online.com/index.php?threads/jerky-xy-motion.1047/ ?

    Or something else?

    It's not a massive effect but a simple form like this is a good place to analyse it and the knowledge will be useful elsewhere.

    The second image shows the cylinder on its side in S3d. You can see the Mesh. The mesh seems to be rather finer than the banding.

    Hmmm. So ringing?

    We see that slowing it down solves the problem, but who wants to do that?

    So if I reduce the weight of the print head (Pro Box: Titan / pancake motor) what effect will that have?

    IMG_0295.jpg

    mesh.jpg
     
    #1 R Design, May 12, 2016
    Last edited: May 12, 2016
  2. Miasmictruth

    Miasmictruth Well-Known Member

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    What speed are you running? I believe for the cylinder print I found that above 35mm/s it was prone to run into the 8bit electronics wall.

    Also what firmware are you running with what type of extruder assembly? If for example you had 1.1 firmware with a 1.0 dual head or something like that your print head acceleration may be to high, I cant get to my bigbox right now or I could give you directions to find the values through the LCD,

    If you just scroll through the menus a bit you should be able to find it. With a full 1.0 carriage the value should be around 400 with the 1.1 Titan i believe the firmware is up to 1000
     
  3. Miasmictruth

    Miasmictruth Well-Known Member

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    Sorry didn't see you posted a speed. Something I noticed with the cylinders and S3D vs Slic3r, at least in the one experiment that I did, Slic3r actually capped the speed around the cylinder at about 35mm/s I don't know if this is some sort of coincidence or if it somehow calculated the number of instructions per second and throttles the feed rate automatically somehow

    With S3D the the moves were whatever the max I put it was set to.
     
  4. R Design

    R Design Well-Known Member

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    Currently I've the 1.0 Pro (single) printhead / extruder.

    Acceleration (default Pro) 600mm/s2;

    S3d slicer;

    1.1 RC3 v2 (latest official);
     
  5. Miasmictruth

    Miasmictruth Well-Known Member

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    You might be experiencing what I did when slicing with S3D, I bed you would get a clean print at 35mm/s

    If it is, thats the wall you it with 8bit electronics. Try printing a similarly sized cube at the same speed it will probably be OK as it has far less instructions to execute, I am sure you are aware that circles on a 3d printer are really just numerous tiny straight lines
     
  6. Brian Dowling

    Brian Dowling Active Member

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    I've been curious about Arc support since I read this comment. Is Slic3r creating gcode for arcs? Is it the only one?

    Arc support
    Slic3r can find curves that, although broken into segments, were meant to describe an arc. Marlin is able to print those arcs. The advantage is that the firmware can choose the resolution, and can perform the arc with nearly constant velocity, resulting in a nice finish. Also, less serial communication is needed.​


    Re: http://reprap.org/wiki/Marlin#Arc_support
     
  7. Miasmictruth

    Miasmictruth Well-Known Member

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    Interesting, might explain the difference's in mm/s of the moves I was observing in the G code between the slicers. If Slic3r is capable of recognizing curves it may also be capable of scaling the speed for 8bit electronics maybe. I re sliced my model a few times with various speed settings but never changed the output code about 35mm/s
     

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