Error while designing a ring: CGAL error in CGAL_Nef_polyhedron3()
Hi!
I'm new to openscad and wanted to make a ring for my girlfriend to
3D-print, but I get the following error:
ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion
violation! Expr: e->incident_sface() != SFace_const_handle() File:
/mxe/usr/x86_64-w64-mingw32.static.posix/include/CGAL/Nef_S2/SM_const_decorator.h
Line: 329
Seems to be a problem with selfintersecting elements:
https://github.com/openscad/openscad/issues/791
Now my question: How can I avoid that? I dont know whats self intersecting,
maybe one of you has a solution.
Here my code:
reso=100; //500;
ring_aussen = 22;
ring_innen = 17.86;
ring_hoch = 6;
ring_rand = 2.5;//1.85;
dellenfaktor = 3.5;
ring_num_dellen = 360/dellenfaktor;
cubedim = ring_aussen+10;
diff = 0.4;
winkel = rands(-45,45,ring_num_dellen*dellenfaktor+1,123);
difference(){
rotate_extrude(convexity = 2, $fn = reso)
translate([ring_aussen/2-ring_hoch/2-ring_rand, 0, 0])
circle(r=ring_hoch/2+ring_rand, $fn=reso);
cylinder(r=ring_innen/2, h=ring_hoch*1.5, center=true, $fn=reso);
translate([0, 0, cubedim/2+ring_hoch/2])
cube(cubedim, center=true);
translate([0, 0, -cubedim/2-ring_hoch/2])
cube(cubedim, center=true);
for ( i = [0 : ring_num_dellen] ){
rotate([0,0,i*dellenfaktor])
translate([ring_aussen/2-ring_hoch/2-ring_rand, 0, 0])
rotate([0,winkel[i],0])
translate([(ring_hoch/2+ring_rand)*2-diff, 0, 0])
cube((ring_hoch/2+ring_rand)*2, center=true);
}
}
I'm new to openscad and wanted to make a ring for my girlfriend to
3D-print, but I get the following error:
ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion
violation! Expr: e->incident_sface() != SFace_const_handle() File:
/mxe/usr/x86_64-w64-mingw32.static.posix/include/CGAL/Nef_S2/SM_const_decorator.h
Line: 329
The rotate_extrude is not a manifold because the circle is touching the Y
axis. Just translate it a little bit to the right. Nice and simple design.
A simpler alternative would be to rotate_extrude the ring section. That
would avoid a non-manifold with any reasonable change of parameter values.
Something like this:
module section() {
difference() {
translate([ring_aussen/2-ring_hoch/2-ring_rand+.1, 0, 0])
circle(r=ring_hoch/2+ring_rand, $fn=reso);
square([ring_innen, ring_hoch*1.5],center=true);
translate([0, cubedim/2+ring_hoch/2])
square(cubedim, center=true);
translate([0, -(cubedim/2+ring_hoch/2)])
square(cubedim, center=true);
}
}
Em qui., 18 de jun. de 2020 às 15:30, Ronaldo Persiano <
rcmpersiano@gmail.com> escreveu:
I'm new to openscad and wanted to make a ring for my girlfriend to
3D-print, but I get the following error:
ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion
violation! Expr: e->incident_sface() != SFace_const_handle() File:
/mxe/usr/x86_64-w64-mingw32.static.posix/include/CGAL/Nef_S2/SM_const_decorator.h
Line: 329
The rotate_extrude is not a manifold because the circle is touching the Y
axis. Just translate it a little bit to the right. Nice and simple design.
A, thanks for the code Ronaldo, I see what you mean. After googling a bit
more I now know that its better to design in 2D and go 3D later in regards
to computation time, so your code helps me with that! :)
Additionally I found another way to solve my problem. Sometimes its better
to take a step back, look at what you've done and hit your head against a
wall. I don't need a complicated tube in ring-shape to then cut away
pieces. If I replace the following from my code:
rotate_extrude(convexity = 2, $fn = reso)
translate([ring_aussen/2-ring_hoch/2-ring_rand, 0, 0])
circle(r=ring_hoch/2+ring_rand, $fn=reso);
with a sphere like so:
sphere(r=ring_aussen/2, $fn=reso);
everything works exactly the same for what I want to do. But again, it's
starting with 3D objects, so your way seems better to me. Hope your and my
way help somebody else who stumble across our posts in his search for
answers.
On a sidenote: I'm 33 now, I grew up as a nerd with the possibilities of
the internet, yet it astounds me every time I see it in little details like
auto-generated parts around mails that I'm communicating with somebody
approximately 2300KM away. You're (I believe) portuguese, I'm german, yet
we talk in english. So thank you stranger and have a good day :)
Am Do., 18. Juni 2020 um 16:55 Uhr schrieb Ronaldo Persiano <
rcmpersiano@gmail.com>:
A simpler alternative would be to rotate_extrude the ring section. That
would avoid a non-manifold with any reasonable change of parameter values.
Something like this:
module section() {
difference() {
translate([ring_aussen/2-ring_hoch/2-ring_rand+.1, 0, 0])
circle(r=ring_hoch/2+ring_rand, $fn=reso);
square([ring_innen, ring_hoch*1.5],center=true);
translate([0, cubedim/2+ring_hoch/2])
square(cubedim, center=true);
translate([0, -(cubedim/2+ring_hoch/2)])
square(cubedim, center=true);
}
}
Em qui., 18 de jun. de 2020 às 15:30, Ronaldo Persiano <
rcmpersiano@gmail.com> escreveu:
I'm new to openscad and wanted to make a ring for my girlfriend to
3D-print, but I get the following error:
ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion
violation! Expr: e->incident_sface() != SFace_const_handle() File:
/mxe/usr/x86_64-w64-mingw32.static.posix/include/CGAL/Nef_S2/SM_const_decorator.h
Line: 329
The rotate_extrude is not a manifold because the circle is touching the Y
axis. Just translate it a little bit to the right. Nice and simple design.
If I replace the following from my code:
rotate_extrude(convexity = 2, $fn = reso)
translate([ring_aussen/2-ring_hoch/2-ring_rand, 0, 0])
circle(r=ring_hoch/2+ring_rand, $fn=reso);
with a sphere like so:
sphere(r=ring_aussen/2, $fn=reso);
everything works exactly the same for what I want to do.
Not exactly the same. It will depend on the random numbers you generate
because with rotate_extrude you are carving a torus surface and not a
sphere. If the random carving cut out all the rounded surface, then they
will be the same.
A side note on your side note: I live in Portugal now but I am from Brazil.
Have a good day!