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Crazy Circles in CAD Drawings

Discussion in 'CNC Tutorials' started by SignTorch, 4/28/23.

  1. SignTorch

    SignTorch Artist

    • Vinyl CuttingVinyl Cutting, CNC RouterCNC Router, Designer / ArtistDesigner / Artist, Hobby / PersonalHobby / Personal
    • Corel DrawCorel Draw, Adobe PhotoshopAdobe Photoshop, V-Carve ProV-Carve Pro
    Vidor, TX
    When you see wild, crazy circles in drawings, it is due to the arc start and end angles getting reversed

    instead of tracking a small section of an arc, it tracks the opposite part which is a nearly complete circle

    in gcode G2 and G3 codes might be swapped - in dxf the 50 and 51 arc group codes might be swapped, or the 42 polyline bulge factor group code is negated

    not sure how that happens but its not a rare phenomenon - some software either reads or writes those codes backwards

    the way the arcs here repeat vertically suggests there is a series of tiny nearly straight nearly vertical arcs with a substantial radius and a miniscule included angle subject to rounding errors on the x coordinates of the arc end points - especially if the y coordinates straddle the arc centerline -

    as shown in the exagerated colored diagram - the problem is in getting the red part of the arc instead of the blue part

    arcinv. invarc.

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