Hi, How do I solve this error? ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion violation! Expr: pe_prev->is_border() || !internal::Plane_constructor::get_plane(pe_prev->facet(),pe_prev->facet()->plane()).is_degenerate() File: /opt/mxe/usr/x86_64-w64-mingw32.static/include/CGAL/Nef_3/polyhedron_3_to_nef_3.h Line: 251 This is the code (Wheel_Guide.stl is attached) difference(){ union(){ translate([12.5,7.7,4.4]) cube([40,2,20.6]); translate([52.55,24,15]) rotate([0,90,0]) cylinder(h=4.8,r=3,$fn=60); import("Wheel_Guide.stl",convexity=10); } translate([11.6,13,4.8]) cube([41,1.1,22]); translate([52,23,15]) rotate([0,90,0]) cylinder(h=6,r=2.65,$fn=60); translate([40,32,-0.1]) cube([20,2,30]); } https://reprap.org/forum/read.php?313,705715,705715#msg-705715 Tue, 19 May 2026 03:38:51 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?313,705715,706485#msg-706485 https://reprap.org/forum/read.php?313,705715,706485#msg-706485 I came to the same conclusion and have designed the part using the original as a guide.
I did try and repair the modified stl but every program I tried did not find any errors.... strange.
It would have been interesting to discover the reason for the error so perhaps I could avoid whatever it is in the future.

Paul]]> appjaws1 OpenSCAD Sat, 10 Sep 2016 10:08:24 -0400 https://reprap.org/forum/read.php?313,705715,705800#msg-705800 https://reprap.org/forum/read.php?313,705715,705800#msg-705800 netfabb.azurewebsites.net] which currently seems to hang so I could not try it). I have a feeling that there is something amiss with that STL, because if I load it into Slic3r and then export as an STL (which will repair some STLs), Silc3r creates an invalid STL.

However the STL shape seems to be fairly simple, so my next step would be to model the entire thing with OpenScad. You can temporarily keep the STL imported to use as a template for your code, rendering with F5 to check dimensions & positions.

Dave]]> dmould OpenSCAD Wed, 07 Sep 2016 10:30:19 -0400 https://reprap.org/forum/read.php?313,705715,705715#msg-705715 https://reprap.org/forum/read.php?313,705715,705715#msg-705715 How do I solve this error?

ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion violation! Expr: pe_prev->is_border() || !internal::Plane_constructor::get_plane(pe_prev->facet(),pe_prev->facet()->plane()).is_degenerate() File: /opt/mxe/usr/x86_64-w64-mingw32.static/include/CGAL/Nef_3/polyhedron_3_to_nef_3.h Line: 251

This is the code (Wheel_Guide.stl is attached)

difference(){
union(){
translate([12.5,7.7,4.4]) cube([40,2,20.6]);
translate([52.55,24,15]) rotate([0,90,0]) cylinder(h=4.8,r=3,$fn=60);
import("Wheel_Guide.stl",convexity=10);
}
translate([11.6,13,4.8]) cube([41,1.1,22]);
translate([52,23,15]) rotate([0,90,0]) cylinder(h=6,r=2.65,$fn=60);
translate([40,32,-0.1]) cube([20,2,30]);
}]]> appjaws1 OpenSCAD Wed, 07 Sep 2016 04:25:19 -0400