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Runaway Machine and Line

Discussion in 'CAM' started by cacope.nc, Feb 5, 2017.

  1. cacope.nc

    cacope.nc New

    Dec 27, 2016
    Likes Received:
    I have a C-beam machine being controlled by Grbl Panel.
    when drawing a design on paper with the machine, the pen should stop, lift and move to other location. Instead, the pen keeps moving in a line in the direction between the two points. The pen should stop at the arrow in the picture below.
    crown failure.jpg

    The gcode stopped bolded lines shown in the section of code below. This gcode was developed using ink scape and MakerCam.

    (Generated by PartKam Version 0.05)
    G20 G90 G40
    (follow path 1)
    G0 Z0.5
    (T0 M6)
    G0 X9.6728 Y1.6736
    G3 X9.6655 Y1.6138 I2.0421 J-0.2789
    G2 X9.6591 Y1.5595 I-2.4615 J0.2631
    G2 X9.655 Y1.5326 I-0.6064 J0.0784
    G2 X9.6233 Y1.3867 I-1.7961 J0.3138
    G2 X9.5169 Y1.0026 I-12.5677 J3.275
    (G2 X9.5151 Y1.003 I575.8389 J3144.4886)
    (G2 X9.5115 Y1.0036 I2301.836 J12569.6144)
    G3 X9.014 Y1.0934 I-17.817 J-97.2928
    G3 X8.756 Y1.138 I-4.6455 J-26.1203
    G3 X8.325 Y1.2062 I-3.9146 J-23.3448
    G3 X7.9432 Y1.2589 I-2.7188 J-18.2727
    G3 X6.985 Y1.3549 I-2.2534 J-17.6704
    G3 X5.9175 Y1.4066 I-1.5955 J-21.8844
    G0 Z0.5
    (Left Half Crown Outline)
    G0 X5.9182 Y8.5324
    G1 Z-0.0098 F320
    G3 X5.7843 Y8.6498 I-0.6466 J-0.602 F320
    G0 Z0.5
    When the bolded lines were commented out, the program ran normally.

    Why did the code fail? My idea is that large number in the I & J numbers caused GRBL to fail.. Can anyone tell me why??
  2. snokid

    snokid Journeyman

    Oct 11, 2014
    Likes Received:
    I and J are the values to arc center.

    the large numbers the largest being over 3 meters(assuming this is in mm)
    that should be hitting either your soft limits or hard limits depending on what you have set up.
    With a c-beam machine I'm guessing your machine isn't as big as a house!!! LOL
    I'm guessing you have something off screen in inkscape....
    hope that helps
  3. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder Resident Builder

    Aug 6, 2013
    Likes Received:
    Those 2 lines are very short arcs with very large radii and so long as the controller is in relative IJ mode they should not pose a problem.

    Put a
    just after the line with G90 in it. This will ensure that GRBL is in relative IJ mode.

    GRBL should remember this setting so you should not have to put this in every file.
    (unless you have files that unset it with a G90.1 !)
  4. cacope.nc

    cacope.nc New

    Dec 27, 2016
    Likes Received:
    Thank You everyone, I also reviewed my inkscape file and found the start of the overrun was at a node with long handle and minor angle. I straighten the node and shortened the handle and re-calculated g-code in MakerCam. Then, I re-ran the ink drawing on the cnc and found it ran properly with no runaway.

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