union(){
difference(){
import("D:/Core XY/D-Bot_latest/files/1-Hotend_Clamp_E3Dv6.stl",convexity=10);
translate([0,0,-0.5]) cube([50,20,43]);
translate([0,20,4]) cube([50,30,43]);
}
translate([13,23.5,0]) cube([15,12,4]); //fillin
}
Using F5 this displays properly but F6 render just ends up with the fillin and no Hotend clamp/

This is the error
ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion violation! Expr: e_below != SHalfedge_handle() File: /mxe/usr/x86_64-w64-mingw32.static.posix/include/CGAL/Nef_3/SNC_FM_decorator.h Line: 426

Am I doing something wrong?

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1

Have you tried to clean up the stl file?

[www.formware.co]

Probably a problem with STL. We can't reproduce unless you provide STL.

The free IdeaMaker slicer from Raise3d has automatic STL repair. You can import, repair, then export from it. There are other approaches as well.