[OpenSCAD] Newbie question

tjhowse tjhowse at gmail.com
Thu May 23 02:42:40 EDT 2019


I've long incorporated a "zff = 0.0001" factor - Z-Fight Fudge, to get rid
of the annoying tenuous pseudo-surfaces you get when subtracting with
overlapping co-planar faces. It's not an elegant solution but it works.

On Thu, 23 May 2019 at 16:18, lar3ry <lar3ry at sasktel.net> wrote:

> G. Wade Johnson wrote
> > The problem in both cases is a subtle issue that we all dealt with. The
> > shape you want to difference cannot be the exact same length as shape
> > you are subtracting from. Otherwise, you end up with a very thin
> > membrane at each end.
>
> Are you speaking of the preview? If so, I would not consider that a
> membrane. It's congruent surfaces interfering with the preview. The render
> gives exactly what I would expect, a hollow cylinder.
>
>
> > Try
> >
> > difference() {
> >    translate([0,37,15]) rotate([90,0,0]) cylinder(h=20,r=5);
> >    translate([0,37,15]) rotate([90,0,0]) cylinder(h=21,r=4);
> > }
> >
> > I normally have a constant eps, defined at the top of my file, that I
> > add to the lengths like this to make it obvious that I am using a fudge
> > factor
> >
> > eps=0.01;
> >
> > difference() {
> >    translate([0,37,15]) rotate([90,0,0]) cylinder(h=20,r=5);
> >    translate([0,37,15]) rotate([90,0,0]) cylinder(h=20+eps,r=4);
> > }
> >
> > The second example works the same way with a small addition (like eps),
> > Doesn't work as well, adding a 1. (Wall thickness is not what you
> > expect in that case.)
>
> I don't get it. The two examples you gave resulted in exactly the same
> object.
> Yes I do realize that this can sometimes create an STL that has errors, but
> if that happens, THAT's when I take steps to get rid of the problem.
>
> Larry
>
>
>
> --
> Sent from: http://forum.openscad.org/
>
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