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Thread: Arc rejection problem

  1. #1
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    Unhappy Arc rejection problem

    Hello All,
    I have a problem with KMotion on my lathe I don't understand. I have a turning shape generated in fusion 360. I can run it in Mach 3 all through to the end. The code is generated as Fanuc turn. When I try to run the same code with KMotion I have to delete the G50 and G54 lines. It then runs until it gets to the first G3 arc command. It stops and gives the message -Radius to end differs from radius to start. I have seen the same problem anytime I try to do manual code it will not run an ellipse. It seem it will only accept a true arc.Is there a setting in K motion I need to change? Thanks for any help.
    Scott

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  2. #2
    Community Moderator ger21's Avatar
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    Default Re: Arc rejection problem

    Could be because Mach3 has a "feature" that allows you to run arcs that are not true arcs. I believe that Mach3 will allow endpoints of arcs to be off by as much as 0.5"
    Most other controls won't allow this.

    Gerry

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


  3. #3
    Gold Member TomKerekes's Avatar
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    Default Re: Arc rejection problem

    Hi Scott,

    Did you do the math? Are the beginning radius and ending radius different? KMotionCNC only allows incremental IJK (arc center is relative to previous point).

    The latest Versions allow you to specify an allowed tolerance.

    Maybe you are in the wrong plane? G17 G18 G19

    Post a code fragment that fails.

    Regards

    TK
    http://dynomotion.com


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    Default Re: Arc rejection problem

    It would seem that since this code is meant to run in Fanuc controls that it would be pretty widely accepted. Where would I look in the KMotion files to see if I can change the setting to allow tollerance in the arcs? I have included a snip of the code. It is line 38 that will not run.

    Thanks,
    Scott

    Attached Thumbnails Attached Thumbnails Arc rejection problem-fanuc-turn-test-snip-png  


  5. #5
    Gold Member TomKerekes's Avatar
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    Default Re: Arc rejection problem

    Hi Scott,

    I did the math. Please check me. Take the previous position and add IK to get the center. Then compute the lengths from the start and end to the centers.

    There is 0.01492 difference. That is quite large. I wouldn't recommend allowing it. You should investigate why your code generator has such a large error.

    The Tolerance is on the Tool Setup | Trajectory Planner Screen.

    Arc rejection problem-radiusdifference-png

    Regards

    TK
    http://dynomotion.com


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    Default Re: Arc rejection problem

    Thanks for your help Tom. I will review and try to understand the arc generation process better. In this instance where Mach allows it and kMotion does not, does that mean the arc may be machined differently on multiple passes or just that it will have the same error each pass?



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    Gold Member TomKerekes's Avatar
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    Default Re: Arc rejection problem

    Hi Scott,

    If the GCode is consistent I would expect the motion to be consistent, but misplaced and with a discontinuity (jump) between the end of the arc and the beginning of subsequent motion path.

    Regards

    TK
    http://dynomotion.com


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    Default Re: Arc rejection problem

    One last question Tom. Is there a post you recommend to use for turning with KMotion?
    Thanks,
    Scott



  9. #9
    Gold Member TomKerekes's Avatar
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    Default Re: Arc rejection problem

    Hi Scott,

    Alexander contributed one here you might try:
    Known KMotionCNC CAD/CAM Post Processors - Dynomotion

    Regards

    TK
    http://dynomotion.com


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    Default Re: Arc rejection problem

    Thanks for all your help Tom. I will give that a try.
    Scott



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Arc rejection problem

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