Unexpected Print Speed Drop

Discussion in 'Calibration, Help, and Troubleshooting' started by rvator, Jul 26, 2017.

  1. rvator

    rvator Active Member

    Joined:
    Sep 20, 2016
    Messages:
    28
    Likes Received:
    6
    I am printing 3DLabprint RC-Planes. The Airframe consists of one outer shell and an internal structure. I rrealized irregular bumps on the outer shell at a positions where also internal structure exists.. Firts I thougt the internal structure comes thru. But after closer observation I realised that at the bumps a short speed drop happens. I think due to the speed drop to much Filament flows out of the nozzle because of the higher pressure inside the nozzle from faster print Speed before.

    - Cura 2.6.2
    - Rumba Board.
    - There in no G1 Fxxx comand in the gcode with a reduced print speed.

    Any idea what this speed drop could cause?



    DSCF6203_k.jpg DSCF6205_k.jpg DSCF6206_k.jpg
     
  2. Spoon Unit

    Spoon Unit Well-Known Member

    Joined:
    Sep 6, 2015
    Messages:
    1,095
    Likes Received:
    322
    Slicer settings could cause the drop to a lower speed. Could also just be the physics of many small co-located extrusions appearing to be slow speed. Pressure in the nozzle is something which can also be typically controlled by slicer settings (in S3D check out Coast at End and Coasting Distance), but can also be something controlled by printer firmware (http://marlinfw.org/docs/features/lin_advance.html).
     
  3. A Dragon In A Pie Costume

    A Dragon In A Pie Costume Well-Known Member

    Joined:
    Jul 6, 2016
    Messages:
    204
    Likes Received:
    15
    marlin rc8 had this issue, upgrading to the full release will solve it, might i ask if you are using any microstepping?
     
  4. rvator

    rvator Active Member

    Joined:
    Sep 20, 2016
    Messages:
    28
    Likes Received:
    6
    If I remember right, I had this issue with RC8 but the speed drops where more noticeable there and over a longer period. I think I solved this with Marlin bugfix-1.1.x.

    At the moment I suppose it has somthing to do with the slicer (Cura 2.6.1), because the very short speed drops occures while printing the outer wall but always at a station where internal structure adjoins.

    Yes, I am using microsteps: X-axis 16, Y-axis 8
     
    #4 rvator, Jul 28, 2017
    Last edited: Jul 28, 2017
  5. Spoon Unit

    Spoon Unit Well-Known Member

    Joined:
    Sep 6, 2015
    Messages:
    1,095
    Likes Received:
    322
    When I "upgraded" to Marlin 1.1, I found that the filament change procedure had, for some reason, inserted a new dependency on the temperatures re-stabilizing, that, for some reason at the time, I had trouble with. But I didn't really want it inserting that stabliization. Anyway one else use this feature and found a way to disable the extra stabilization?
     
  6. rvator

    rvator Active Member

    Joined:
    Sep 20, 2016
    Messages:
    28
    Likes Received:
    6
    I continued the investigation of my issue. I looked closer at the gcode and plotted the path of one outer wall. At the position where the speed drops occur there are more and closer located points (G1 commands) in the gcode. See figure 1.

    Gcode_Plot.JPG
    Here are examples of the original gcode for three print speeds (60,70,80mm/s)
    Org.jpg


    Then I deleted the points laying close together in the gcode by hand ( for a 4mm height and only in the front part) and printed the part again. Nearly all of the spedd drops during print disappeared!

    And here the result after deleting some points:

    Edit.jpg

    Could it be, that for points laying to close together a speed limit for the rumba board is reached ant it can't process the points in realtime?

    There is no reason for producing points so close together, but that is another problem concerning cura.
     
  7. dc42

    dc42 Well-Known Member

    Joined:
    Aug 16, 2016
    Messages:
    173
    Likes Received:
    70
    Are you printing from SD card, or over USB?
     
  8. rvator

    rvator Active Member

    Joined:
    Sep 20, 2016
    Messages:
    28
    Likes Received:
    6
    Have the issue with both USB (Repetier) and SD card
     
  9. dc42

    dc42 Well-Known Member

    Joined:
    Aug 16, 2016
    Messages:
    173
    Likes Received:
    70
    Can you share the gcode around those points? It may be that Cura isn't maintaining a uniform extrusion rate when the spacing is small - the fact that Cura insists on using absolute extruder coordinates makes this more likely. I've seen this happen with the code for printing skirts that Cura generates.
     
  10. rvator

    rvator Active Member

    Joined:
    Sep 20, 2016
    Messages:
    28
    Likes Received:
    6
    I already checked the Extrusion rate. I calculated the relativ extrusion from point to point and divided throu the total (X+Y) relative movement from point to point. I think it looks ok.


    Extrusion.JPG


    Still believe, the problem comes from the short speed drops but at the moment I cant say why they occur.
     

    Attached Files:

Share This Page