title: OpenSCAD render is empty
body: <p>I’m in the process of designing a helix, and have done the blade in AutoCAD, to later on export it to .stl and finish the design in OpenSCAD.</p>
  
  <p>The problem here is that when I try to render it (F6), the result is incomplete (only Joints.stl shows up). Although I have tried to fix both .stl files several times, the problem persists.</p>
  
  <p>Thanks in advance</p>
  
  <p>Edit: If it helps I made the .stl using AutoCAD and Blender.</p>
  
  <p>(this is my code)</p>
  
  <pre><code>module pal() {
  
      translate([1.5,100,0.2])
          rotate([0,-10,0])   
  import("Helix_Final.stl", convexity=100);
  
  }
  pal();
  rotate([0,0,120])
      pal();
  rotate([0,0,-120])
      pal();
  
  translate([0,0,8.4])
  import("Joints.stl");
  </code></pre>
  
  <p><a href="https://drive.google.com/uc?authuser=0&amp;id=1EpiPwwBbHvDU-XiVnH4-6qGgI6qFOPBP&amp;export=download" rel="nofollow noreferrer">Helix_Final.stl</a>
  <a href="https://drive.google.com/uc?id=1-MqW6KNoeSvJoWMKQ1P3MCsRnlzfRvlu&amp;export=download" rel="nofollow noreferrer">Joints.stl</a></p>
  
  <p>It also gives the following log:</p>
  
  <pre><code>Saved backup file: C:/Users/eleme/Documents/OpenSCAD/backups/Joints¿-backup-
  qHp13132.scad
  Compiling design (CSG Tree generation)...
  Rendering Polygon Mesh using CGAL...
  ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion violation! 
  Expr: e-&gt;incident_sface() != SFace_const_handle() File: /opt/mxe/usr/x86_64-w64-
  mingw32.static/include/CGAL/Nef_S2/SM_const_decorator.h Line: 326 
  ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion violation! 
  Expr: e-&gt;incident_sface() != SFace_const_handle() File: /opt/mxe/usr/x86_64-w64-
  mingw32.static/include/CGAL/Nef_S2/SM_const_decorator.h Line: 326 
  ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion violation! 
  Expr: e-&gt;incident_sface() != SFace_const_handle() File: /opt/mxe/usr/x86_64-w64-                
  mingw32.static/include/CGAL/Nef_S2/SM_const_decorator.h Line: 326 
  Geometries in cache: 8
  Geometry cache size in bytes: 11954368
  CGAL Polyhedrons in cache: 1
  CGAL cache size in bytes: 1378168
  Total rendering time: 0 hours, 0 minutes, 11 seconds
     Top level object is a 3D object:
     Simple:        yes
     Vertices:      661
     Halfedges:    3182
     Edges:        1591
     Halffacets:   1864
     Facets:        932
     Volumes:         2
  Rendering finished.
  </code></pre>