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  1. #1
    Join Date
    Jul 2018
    Posts
    14

    how to stop arcs from being interpolated

    Hello,

    I draw a circle, extrude, then generate a 2.5D operation "face mill" . The type is spiral. It should be producing gcode with 02/3 arcs. What's wrong here? The program is like 2500 lines.

    -Point interpolation is unchecked.
    -Approximate arc by line is unchecked.
    -Geometry is not silhouette
    -It is not a spline since it is just a circle created in solidworks.
    postprocessor is aweaFANUC

    In visi, the postprocessor does not interpolate, producing the same path of about 50 lines or less. Here it is 2500 and producing poor surface.

  2. #2
    Join Date
    Jan 2012
    Posts
    36

    Re: how to stop arcs from being interpolated

    Hi cryptopsy,

    Unfortunately, there is no gcode command for a spiral. To be a true spiral, the arc (G2/G3) would not work because the spiral is actually a spline that is continuing to change as it gets bigger or smaller. Thus producing a point-to-point gcode.


    Highest Regards,
    Darrin - SolidCAM

  3. #3
    Join Date
    Jul 2018
    Posts
    14

    Re: how to stop arcs from being interpolated

    Quote Originally Posted by Mikay19 View Post
    Hi cryptopsy,

    Unfortunately, there is no gcode command for a spiral. To be a true spiral, the arc (G2/G3) would not work because the spiral is actually a spline that is continuing to change as it gets bigger or smaller. Thus producing a point-to-point gcode.


    Highest Regards,
    Darrin - SolidCAM
    What spiral type should i use to replace the spiral with g2/3 moves? There must be some type that permits this, since i generated it in visi.
    What if i want to do a helical path, would it interpolate arcs? Like in this exact example :
    https://www.youtube.com/watch?v=rg5ucsg-W

  4. #4
    Join Date
    Nov 2012
    Posts
    1267

    Re: how to stop arcs from being interpolated

    Edit: What kind of spirals are we talking about? A flat one ( R=var, Z=const)? Or a downward spiral (R=const, Z=var)?

  5. #5
    Join Date
    Jan 2012
    Posts
    36

    Re: how to stop arcs from being interpolated

    I am assuming that visi did an arc fit during the creation of the spiral. Which means it is not really a spiral but a series of larger/smaller arcs that are connected. I don't see a way to create a true spiral using arcs.

    Regards,
    Darrin - SolidCAM

  6. #6
    Join Date
    Jul 2018
    Posts
    14

    Re: how to stop arcs from being interpolated

    It is a spiral for a facing operation, so it is const Z and it doesn't have to be a true spiral.

  7. #7
    Join Date
    Jun 2010
    Posts
    4252

    Re: how to stop arcs from being interpolated

    A true spiral has a constantly changing radius of curvature.Neither CAM programs nor g-code can handle that.
    However, one can do a very good approximation by doing a number of 180 degree segments at decreasing radii.

    Cheers
    Roger

  8. #8
    Join Date
    Jan 2005
    Posts
    15362

    Re: how to stop arcs from being interpolated

    Quote Originally Posted by RCaffin View Post
    A true spiral has a constantly changing radius of curvature.Neither CAM programs nor g-code can handle that.
    However, one can do a very good approximation by doing a number of 180 degree segments at decreasing radii.

    Cheers
    Roger
    Give me any possible curvature or spline you can come up with and I'm sure I can make the G-code for it in my cam program

    Here is a Spiral took me all of 2 minute's start to finish, of course it is not a true spiral, but anything is possible with a good cam program, the cam software I use has had this operation for about 15 years may be longer has many more useful operations like this
    Mactec54

  9. #9
    Join Date
    Jan 2012
    Posts
    36

    Re: how to stop arcs from being interpolated

    cryptopsy,

    RCaffin is correct, you can draw the path in pretty simply if you really want a spiral like path without so many lines.

    Darrin - SolidCAM

  10. #10
    Join Date
    Jul 2018
    Posts
    14

    Re: how to stop arcs from being interpolated

    Quote Originally Posted by RCaffin View Post
    A true spiral has a constantly changing radius of curvature.Neither CAM programs nor g-code can handle that.
    However, one can do a very good approximation by doing a number of 180 degree segments at decreasing radii.

    Cheers
    Roger
    Visi generates this automatically. I should not have to draw my own spirals, because if i want to change the width of cut , or i change the tools, i have to redraw the spiral.

  11. #11
    Join Date
    Jun 2010
    Posts
    4252

    Re: how to stop arcs from being interpolated

    I use a parametric program for spirals. Take radius R of spiral area, divide by 0.8*D, where D is the tool diameter, and you have the number of full loops needed. Both R & D are editable parameters. The 0.8 allows for path overlap. It's just maths, which g-code is well able to handle.

    Cheers
    Roger

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