modifications to OpenSCAD. Here is why.
OpenSCAD uses the cgal.org geometry engine. OpenSCAD uses 2 of CGAL's
1. Nef Polyhedron
2. "Ordinary" Polyhedron
file output. CGAL requires that conversion from Nef poly to 'ordinary' poly
be done only on 2 manifold shapes.
structure and pull out triangles. Its quite a bit of work.
Ah
I thought it might have been the many coincidental points of
intersection. I fixed it
by offsetting the three sets of cross beams by +/0/- epsilon (the beams
are 1mm, epsilon is 0.01mm).
That produced some slivers at the boundary of the cylinder, so I ALSO
reduced the size of the cylinder by epsilon.
It's all good now - all of these features are just at the limit of what
my PLA printer will print so that the resulting object is robust (i.e.,
doesn't fall apart).
But
now I wonder - it seems that OpenSCAD has a design decision to NOT
export STL if the result is not manifold. I think this is a mistake
(especially since there are no tools to help you fix the non-manifold
vertices, or even LOCATE them). In my opinion, a better choice would be to
output the STL with a warning (STL is perfectly capable of representing all
sorts of evil surfaces!). Then, I could use MeshLab or netfabb to repair
the mesh. As it is, I can't get my hands on the mesh to try to repair it.
or
can I? Is there something I'm missing?
--
Kenneth Sloan
Post by Marius KintelPost by Kenneth SloanWhy is this not a manifold surface? Is this a bug in OpenSCAD? How
can I work around it?
Post by Marius KintelHm, it looks like you have a freak intersection exactly on four point
on your cylinder, causing it to create four linear objects with no volume.
Post by Marius KintelMaking your cylinder a tiny bit smaller seems to fix it.
-Marius
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