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What is the right way to make cross section?

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What is the right way to make cross section?

OpenSCAD mailing list-2
Hi,

I am probably trying the wrong way to make a cross section.  In general, I do:


difference(){
  union(){
    module1();
    module2();
    .....
    .....
   modulen();
 }
   rotate([200,0,0])
    rotate([0,90,0])
    linear_extrude(height=70,center=false,convexity=10)
    polygon([[0,0],[50,20],[-50,20],[0,0]]);
}

The problem is that when I open the .scad file in FreeCad to create a 2D b&w drawing, FreeCad puts the back-side view of cutting wedge and the modules also on the page and from there on the whole thing is FUBARed.  See the light gray big triangle and circles on the attached picture.  OpenSCAD does not do it.  So it is obviously a FreeCad issue, but it might be an issue because I am doing the cross section wrongly.
I am looking forward to any hint that shows me the right way, so I can do my little project.

Thanks ahead,
Infocean



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Re: What is the right way to make cross section?

JordanBrown
What you are doing looks plausible, but a concrete runable example would be helpful.

In what you show, the only thing I would be concerned about is that one edge of your wedge is on the x=0 plane, and if your model is also based on the x=0 plane then you could have a Z-fighting problem of some kind.

(A Z-fighting problem is, in this case, where you subtract B from A, and they have a face in the same place so the program can't quite figure out whether it's not there, or is there but is zero thickness.)

The normal solution to such a problem is to shift the "negative" object just a little so that there's no ambiguity.


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