Revising the model with Simplify3d, I can see the holes in it only after
slicing. It seems that the distance between the front and back surfaces in
those areas is much smaller than the filament thread diameter and the
slicer ignore them. Also, there is no observable holes when the model is
loaded in Sketchup (I load it with a fair scale up). So, it seems that
there is no genus in the model but a very very thin wall in some areas.

2018-02-25 19:16 GMT-03:00 Ronaldo Persiano rcmpersiano@gmail.com:

jon_bondy wrote

As Nophead said (his post was delayed, needing approval due to its size
BTW), NetFabb shows it has degenerate triangles. Unlike other issues, it
does not flag these with the big RED Cross.
You need to click on the Red Cross icon, make sure the check box is
selected, also press Update.

You see them as red lines:
http://forum.openscad.org/file/t359/jon_face_sample.jpg

These can generally be fixed (I've had ones it could not), via
Repair/Remove-Degenerated-Faces, I also do an auto repair after JIC.
Nopehead's post/email has the fixed STL attached.

BTW Jon, did you flatten the face to reduce overhangs?? Sorta looks that
way...

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Carsten:

That certainly did fix the problem!  Your tool gets better and better!

Thanks!

Jon

On 2/25/2018 3:26 PM, Carsten Arnholm wrote:

--
Sent from my desktop computer.
I do not receive emails while away from my desk,
nor do I receive texts on my main phone number
(which is a land line).
If you know that I am on the road, please text me.
If you know that I am home, please email me.

On 25/02/18 20:26, Carsten Arnholm wrote:

I guess I'm been asleep, which utility?

On 2018-02-26 10:31, Gadgetmind wrote:

It is a C++ utility I wrote (working name "abm_polyfix") for analyzing
and repairing polyhedra, reading from STL or AMF. It eliminates/merges
close vertices, eliminates zero area faces of various kinds, plus fixes
some non-manifold issues by splitting faces, etc.

Carsten Arnholm

On 26/02/18 10:36, arnholm@arnholm.org wrote:

Cool. Is it available for others to try? Linux friendly?

On 2018-02-26 11:51, Gadgetmind wrote:

The idea is to eventually provide a web service with this + more. This
is ongoing, if delayed. "abm_polyfix" runs on Windows and Linux like
everything I do.

In general I think the thread illustrates the somewhat fuzzy nature of
repairing problematic polyhedra in general and STL files in particular
(STLs do not provide any topology, it must be guessed). Several repair
tools exist but they appear to make different assumptions leading to
different results.

Carsten Arnholm

On 2/26/2018 7:41 AM, arnholm@arnholm.org wrote:

Are there other file formats that would be better?  Getting designers
like OpenSCAD and slicers to both implement something new would be
tough, but if there are clear benefits maybe it could be done.

On 26. feb. 2018 18:35, Jordan Brown wrote:

Yes, there are better formats (see below), but STL seems so entrenched
that it is very hard to get wide enough support for anything else. Some
requirements to a non-STL format I guess would be

1. Suited for polyhedron exchange between CAD applications, not just CAD
   to slicers.

2. Unambiguous format, with explicit topology

3. Efficient binary storage, plus equivalent ascii text version with
   same info. Binary/Ascii should be transparent to users.

4. It must be very simple.

etc.

OpenSCAD already support other 3D formats in addition to STL

OFF - http://paulbourke.net/dataformats/off/
AMF - https://en.wikipedia.org/wiki/Additive_Manufacturing_File_Format

Both of the above satisfy 1) and 2). AMF in its simplest form is quite
nice, but not terribly efficient, plus in my opinion it forgets 4) so it
will never become universal. OFF is a nice contender, but it does not
seem to be simple enough to be popular.

STL is both wasteful and ambiguous, it is just a sea of free floating
triangles. The binary format does not contain the same info as the text
format, etc. Its popularity is due to history only.

It seems to me super simplicity is a key. So any alternative format
should be even simpler than STL. Given that existing alternatives are
not very popular, we might as well propose something new to compete,
making simplicity the key feature while fixing some of the STL issues.
In my mind it could be something like

• simple file header to identify ASCII/Binary
• vertex coordinates stored only once
• triangle faces only
• faces defined by references to vertices, implicit normals

In other words, just the bare minimum, equivalent to the info that goes
into OpenSCAD polyhedron command. The text format would be more compact
than STL and simpler to read. The binary format would also be more
compact than STL since coordinates would be mentioned only once, and
therefore also not have any issues with interpretation.

You could say it is far too simple. But if you want it to be widely
adopted it must be extremely simple and fast. We could call it STL2 and
say it is how STL should have been defined in 1985 or so :-)

I don't have any illusions it would be successful, but if it was adopted
I think it would be helpful in avoiding some of the "damaged STL" issues
(not all) and enable easier sharing of models between various applications.

Just my thoughts, nothing else.

Carsten Arnholm

STL is unambiguous if it is written correctly and only used to represent a
manifold model with no self intersections. That is sufficient for 3D
printing as all 3D printed objects are manifold.

While other representations can also represent non-manifold objects it
pushes the problem downstream. How do you print a non-manifold object?

On 26 February 2018 at 19:44, Carsten Arnholm arnholm@arnholm.org wrote: