Hi

I've been suffering in OpenSCAD with the lack of chamfer and fillet
operations.  Spent time trying to
figure out sweep() (Sorry Oskar, you haven't made something that's readable
or useable; Ronaldo you fixed it.  Sorry Ronaldo, you haven't either, though
your posts have code that are must-haves that a improved, even minimal,
sweep() must have.  Maybe please put it into a downloadable library.  Better
yet get OpenSCAD to incorporate the thing. Jeez.)  Failed.

Here's a simple idea.  CGAL is based on half-spaces, 3D planes with one side
"in" and one side "out"; any triangle in 3-space defines its plane, and a
bunch of them together (with their "in" sides, half-spaces, intersected)
create an arbitrary object surface.  I think this is not news.

But..

Every intersection or union of half-spaces could be softened by a chamfer or
fillet, defined as a plane cutting the corner.  Here's a bad hand
illustration suggesting where and how a fillet can be fitted to the two
planes.

http://forum.openscad.org/file/t3073/IMG-1360_-_Copy.jpg

I don't know how to work with this or the CGAL community.  Please help me
understand, how can we get a modification into CGAL so that
union_with_fillet() and intersection_with_chamfer() are some available
options in the library? And if we did wouldn't it enable OpenSCAD to have
those functions also? Can this be done? How can it be done?  What do you
want me to do if it needs to be done, and what can you do to help it be
done? Yes I am a mere newbie, but hey this is an issue that has plagued and
limited OpenSCAD for many years, let's fix it. I'll try to help where I can.

Tom

Thomas C Veatch PhD
tomveatch.com

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A 3D version of offset() would do that. Sadly, that seems impractical to do
in OpenSCAD code.

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I Hear you. iv'e been peculating for years about this subject. Spoiler
edge-centric chamfer has unsolvable edge cases. In fact you can get into
trouble even in open-cascade based software. But that is not a reason to try
something that work in all sane cases. The user just have to take more adult
care.  I know scary concept.

The Idea was much like your to  make the  boolean of A and B. Make a copy
and trow out all points and edges that was  in the  in the  A/B input
geometry. Now you have a path along the exact boundary of A/B.
http://forum.openscad.org/file/t1678/polytools.png
http://forum.openscad.org/file/t1678/polytools3.png
This boundary could be sweept with some corner function (chamfer
/fillet,pretty). The caveat is that  the boundary branch breaks and that the
surrounding geometry might be to "thin" to support a naive implementation.

Now construct a second boundary offset pushing out on the surface each A and
B.
As A and B not necessarily meat at 90 degree the varying  amount of offset
had to be considered along the boundary depending on what angle A/B meet.
Graceful failure has to be defined each point where no true solution can be
found. At sharp points should radius shrink, adapt  or just run out? so many
ways to mess up.
http://forum.openscad.org/file/t1678/polytools2.png
http://forum.openscad.org/file/t1678/polytools4.png

These three boundaries together is the information needed to construct some
profile sweep on rails.
Said sweep must handle any kind of wild and branching boundary .

This is all in the simplest union case. Cooking up a chamfer  between two
unioned primitives might be doable but from there on the pain begin.

--
Sent from: http://forum.openscad.org/

I Hear you. iv'e been peculating for years about this subject. Spoiler
edge-centric chamfer has unsolvable edge cases. In fact you can get into
trouble even in open-cascade based software. But that is not a reason not to
try something that work in most sane cases. The user just have to take more
adult care.  I know scary concept.

The Idea was much like your to  make the  boolean of A and B. Make a copy
and trow out all points and edges that was  in the  in the  A/B input
geometry. Now you have a path along the exact boundary of A/B.
http://forum.openscad.org/file/t1678/polytools.png
http://forum.openscad.org/file/t1678/polytools3.png
This boundary could be sweept with some corner function (chamfer
/fillet,pretty). The caveat is that  the boundary branch breaks and that the
surrounding geometry might be to "thin" to support a naive implementation.

Now construct a second boundary offset pushing out on the surface each A and
B.
As A and B not necessarily meat at 90 degree the varying  amount of offset
had to be considered along the boundary depending on what angle A/B meet.
Graceful failure has to be defined each point where no true solution can be
found. At sharp points should radius shrink, adapt  or just run out? so many
ways to mess up.
http://forum.openscad.org/file/t1678/polytools2.png
http://forum.openscad.org/file/t1678/polytools4.png

These three boundaries together is the information needed to construct some
profile sweep on rails.
Said sweep must handle any kind of wild and branching boundary .

This is all in the simplest union case. Cooking up a chamfer  between two
unioned primitives might be doable but from there on the pain begin.

--
Sent from: http://forum.openscad.org/