Hey everyone, I am building a model of a plasma table using hiwin linear
rails and bearings.

Hiwin provides CAD files of their stuff, so I grabbed a dxf of the front
profile of the rail I am using and
extruded it in OpenSCAD to my desired length.  This works fine.

I also grabbed an STL of the bearing block (its a more complex shape than
the rail - cant linear extrude), which by itself imports fine.

When I try to render both of these items at the same time, I only see the
rail and get this error in the console:

Rendering Polygon Mesh using CGAL...
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
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

Any suggestions?
Thanks

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It helps if you can share your code. Also point to the STL & DXF.

Looks likely the STL has degenerate faces, you can check if with  Netfabb
Basic http://www.netfabb.com/downloadcenter.php?basic=1  .

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Thank you for your reply.

I ran the analysis in netfabb and I don't notice any problems - I may be
missing something though.

I put all of the files for this, including a netfab screenshot here:

http://files.albersllc.com/cad/

this code is essentially what I have uploaded in the .scad file and has the
same issue:

import("HGH20CA_Z0_C_SS_1.stl");
translate([0,0,20])
rotate([90,0,0])
linear_extrude(height = 1500, center = true)
import (file = "HGR20_rail_front.dxf");

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Hello

To me it seems this is a bug in OpenSCAD. When each part is exported as stl
one at a time and then imported it works well. In my opinion this is one
more reason to have an export() from the script, functionality.

jpmendes

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Hi

Forget my previous message. I made some mistake during my tests. When
importing both .stl the same errors occur.
Sorry for this.

jpmendes

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That is what I expect to see (I hadn't got to the point where I could
position the bearing block on the rail yet but those are the parts)  - When
I get a chance maybe I will try on my girlfriend's mac to see if that makes
a difference.

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Hi

Meshlab doesn't report errors, however Kisslicer does. See pictures:
http://forum.openscad.org/file/n15996/Capture.png
http://forum.openscad.org/file/n15996/Capture3.png

After repairing the model using the online
https://modelrepair.azurewebsites.net/
https://modelrepair.azurewebsites.net/  service
Meshlab start reporting some errors:

http://forum.openscad.org/file/n15996/Capture4.png

Cheers
jpmendes

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Thanks!!  I downloaded kisslicer and just opened and then saved the .stl from
there, using that file all is well.

I really appreciate all of you looking into this

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I wrote a program in AutoCad (older version 14) that reads and draws STL
files. The triangle faces are colored according to the Z value of the normal
vectors.  Triangles with a normal vector value of z=0.0 are RED, z=1.0 are
yellow, z>0.0 are green, z<0.0 are cyan, and z=-1.0 are blue. In the AutoCad
rendering of your STL file there are some faces on the end of your model and
also in some of the holes that appear to be not exactly vertical, although I
doubt that is the cause of your error message.
http://forum.openscad.org/file/n15998/HGH20CA_Z0_C_SS_1.jpg

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