STL files - "totally unusable" ?

From: Vesna Cota (
Date: Fri Apr 14 2000 - 22:06:18 EEST

Hello Jorn and all the others,

I have been reading and listening about this "totally unusable STL files
from AutoCAD and Mechanical Desktop" for years and can't stop wondering
what's going on. I have been creating STL files from AutoCAD since its first
solid modeling extension AME became available. In all those years I seldom
had any problems.

I am using Mechanical Desktop now along with ProE, and you couldn't tell
which one I used to create the STL file. With AutoCAD it is very important
to set your facetres variable to a high value (default is 0.5, highest is
10, I never go below 8). With Mechanical Desktop I still use the AutoCAD
STLOUT command ( which means I explode my parts to make them genuine AutoCAD
solids ), mainly because the MDT amstlout command creates ASCII files and I
prefer smaller and cleaner binary output.
Obviously, once a bad stl file is created it takes much more effort to fix
it ( if possible at all) and it is difficult to know how it compares to the
original part if you don't have both. Before attempting to fix the STL file,
try to create a better STL output.

I never had any problems with metric parts, but it did happen with imperial
units. Because of the settings in AutoCAD, when working in inches the max
facetres setting of 10 may be too small and triangles may end up too big to
represent small radii, making them either disappear or turn into chamfers.
In those cases I would scale up the model (25.4 times as an example, but it
could be 100 or anything else as needed), create the STL output and let the
RP supplier know that the model is scaled up. He would scale the STL output
of the part down and keep the definition at the same time. It's not as
straight forward as typing stlout, but it works every time.

Another option may be to export the SAT file ( acisout in AutoCAD, amacisout
in Mechanical Desktop). Acis file can be imported in many other CAD packages
and the STL file can be exported from there. I never had to use this
approach. The acis file can be checked out using the ACIS viewer from
Spatial Technologies. Great tool, by the way!

If the Acis output doesn't work, I would suspect the part has a flaw.
Ultimately, it boils down to the poor design approach. And that will
generally have more to do with the training of the user than with the
software itself. ... which is a whole new story.

AutoCAD users may need more information regarding generation of good stl
files and some help if it doesn't work out. Hopefully this will provide a
bit of it.

I just started testing the Autodesk Inventor. I'll let you know how it


Vesna Cota
Industry Consultant
RPMV Technologies
10464 Hwy 48
Markham, Ontario
L3P 3J3 Canada

-----Original Message-----
From: []
Sent: Friday, April 14, 2000 10:32 AM
Subject: Re: - a new web service for RP

Jorn and list ;
You are absolutly right. We have recieved many files from Mechanical Desktop

and also the new Inventor from Autodesk. We have the same problem, the STL
files are totally unusable for RP. I have yet to recieve a valid STL file
from an Autodesk product (since 1983). I have the same problems with SDRC so

I guess Autodesk is not alone. It's no wonder why all the STL fix programs
are doing such a brisk business when the major Cad vendors put out such
Its funny we very seldom have any difficulties with ProE, Solidworks, Catia,

or even UG (used to be McAuto). So if it can be done why can't they all do
right. After all none of these systems are shareware, (maybe it is for those

who don't buy it legitimatly). My advise would be if you use this service
the file translated into Step (the international standard exchange format
PDES/STEP). With Step you have the best chance to get the most valid data
into your own native system, then produce your own STL files from there in
your native system. Once the file is tessellated into triangles it is
anybodies guess what is correct and what isn't.

    I have no real problems with ACIS (.sat), Parasolid (.par), or DXF
formats except they are all propriety and not internationally regulated or
licensed by the ISO. Thus they can be changed at any time by the vendors to
keep their competitors guessing Just look at the history of DXF every
is different. Most vendors wrote their DXF translators for Autocad 12 or
earlier and havn't updated the translator since (maybe thats why the DXF
translator is usually free). You get exactly what you pay for.

    Even with its shortcomings I believe this E-based system from Spatial
will have a huge impact on the entire industry (talk about the right idea at

the right time). Who knows they might be the next
My 2 cents
Bob Morton
Fusion Engineering

In a message dated 4/14/00 3:09:41 AM Central Daylight Time, writes:

<< Nice, nice ....

 First Spatial (usw. Autodesk) must fix thier .STL generator in order to be
succesfull in RP. We regulary receive .STL models from Mech.Desktop wich are

a real disaster to handle/repair, and often can't be used for running on our

Genisys FDM.

 Anyone experienced these kind of problems too? We now usually export the
ACIS-kernel-format and switch it to Parasolid-kernel-format (Vero
Visi-series) If we then make a .STL export, in 9 of 10 time a correct .STL
file is made.

 Kind regards,

 Jorn Berends
 JB Ventures BV >>

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