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IndustryArena Forum > CAM Software > BobCad-Cam > Post generating really small erroneous radii circles?
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  1. #1
    Join Date
    Jun 2010
    Posts
    89

    Post generating really small erroneous radii circles?

    Hi again all,
    I am trying to carve out a letter C from a block of material and then run a chamfer along the edge.

    However, my chamfer pass, when posted is producing several arcs with .020 radii that should not be there. I cannot figure out why, or how to eliminate them.

    they are totally extraneous and all lines with radii .020 can be deleted and the post works fine. They seem to occur at sharp the parts of the inside contour where the arcs meet?

    How can I get bobcad to stop producing these small circles?

    As an example the posted code looks like

    Code:
    Arc Ccw X0.8769 Y1.6308 Radius0.515
    Arc Ccw X0.8012 Y1.6353 Radius0.6368
    Arc Ccw X0.7998 Y1.6353 Radius0.6368
    Arc Cw X0.7998 Y1.6353 Radius0.02
    Arc Cw X0.7997 Y1.6353 Radius0.02
    Arc Ccw X0.7966 Y1.6354 Radius0.5923
    I have attached a zip file with the bobcad file, my post, as well as the posted code.

    Appreciate any and all advice please.

    Thanks
    Brian
    Attached Files Attached Files

  2. #2
    Join Date
    Apr 2008
    Posts
    1577

    Re: Post generating really small erroneous radii circles?

    The chamfer feature almost always generates a toolpath with a small offset from the part profile.

    When connecting these offsets, there are two styles, "Intersectional" or "Roll". "Roll" is considered the safest as it keeps the cutter in contact with the part profile. If you look at this picture, you can see the the "Intersectional" style connection causes the cutter to slightly overshoot the corner. Imagine an extreme case like the point of a needle. If the cutter did not "Roll" over the point of the needle, it would really overshoot the corner and could collide with something else you didn't anticipate.

    Note that deleting the radius will cause the chamfer tool to clip the corner. Bad idea.
    Attached Thumbnails Attached Thumbnails C-SBC-2014-05-02-15-28-39.jpg  

  3. #3
    Join Date
    Jun 2010
    Posts
    89

    Re: Post generating really small erroneous radii circles?

    Hi I understand those. But it also generates extra curves not at the corners but at the top bottom and left side of the inside of the c. These are not sharp corners but where two arcs meet. These two arcs at this point should be parallel. It should not be the case you describe. I'm wondering if its because my geometry is imported? Is there overlapping lines or something.

  4. #4
    Join Date
    Apr 2008
    Posts
    1577

    Re: Post generating really small erroneous radii circles?

    It is the geometry for certain. If I explode the splines at the top of of the inside of the C, I get two arcs that are not tangential. Notice the "bad" arcs are in an opposite direction (CW instead of CCW). That's the tool "Rolling" over the "sharp" point there. If they are not tangent or parallel, there will be a small rollover.

    Because these are splines you are dealing with, you may be able to increase or decrease the Spline tolerance value to get rid of them but the geometry is the true culprit.

    Personally, I would try to explode the whole C shape into arcs, then use Reorganize - Make Tangential.

  5. #5
    Join Date
    Jun 2010
    Posts
    89

    Re: Post generating really small erroneous radii circles?

    Thanks SBC. That makes sense. Also, exploding the C into arcs and then reorganizing into tangential arcs made the sharp points go away. Thats great news!

    Brian

  6. #6
    Join Date
    Apr 2008
    Posts
    1577

    Re: Post generating really small erroneous radii circles?

    Glad you got it and sorry if I posted like you were a total newb and had no idea what was going on. It's hard to tell someone's user level in the forums so I just put it all out there.

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