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  1. #1
    Join Date
    Jan 2011
    Posts
    0

    Mach 3 DRO/Gcode doesn't match

    Hey guys. Sort of a noob to CNC, not so much to machining.

    Here's the deal. I've got my CNC machine all set up, and I'm using Mach 3. I can go anywhere in my 98"x50" table within 0.003." I am certain that my backlash is compensated properly, I am not missing any steps, and that my steps per are dead on. In short, if I enter the MDI screen and give a "g0" instruction, the machine goes exactly where I expect it to, and the on-screen DRO and real-life measurements reflect that.

    My problem arises when I am running G-code. My on-screen DRO (incidentally where the real life tool is) gets out of sync with the G-code instructions.

    You can see from the screenshot below that I am stepping the G-Code with the "Single BLK" command and that Mach3 just received the "G1 9.6894" command, but my router actually moved to +9.7064, which is 17 thousanths out! This is verified by real life measurement.


    Here are the links to my G-Code.
    Part I'm discussing
    Other Part I'm having trouble with

    I'm not sure what I'm supposed to do here, the errors seem to be random anywhere up to 0.035". I have tried enabling/disabling backlash compensation (and restarting program like it says), it only makes things worse due to wiggly backlash.

    The crazy thing is, if I stop the G-code, click "goto z" and then goto the MDI page, it now includes that stupid offset. For example "G0 y0.2" goes to +0.217, no matter what I "G0" it adds .017 to it and sends that to the DRO and the machine.

    Please help a confused man.

    Thanks
    -GB Ward

  2. #2
    Join Date
    Mar 2003
    Posts
    35538
    What are your steps/unit set to?
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  3. #3
    Join Date
    Jan 2011
    Posts
    0
    X Axis:
    Steps Per: 1419.221006
    Velocity: 469.68
    Acceleration: 10.019581

    Y Axis:
    Steps Per: 1418.450557
    Velocity: 469.44
    Acceleration: 10.015506

    Z Axis:
    Steps Per: 8024.030299
    Velocity: 30
    Acceleration: 3

  4. #4
    Join Date
    Mar 2003
    Posts
    35538
    How old is that version of Mach3? Looks like 2.63 maybe?

    I'd recommend a newer version first.

    Another guess it's it's related to CV and backlash comp.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  5. #5
    Join Date
    Jan 2011
    Posts
    0
    Thanks. Upgrading appears to work.

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