RE: STL file toolkit

Date: Tue Nov 18 1997 - 02:03:09 EET


> Are STL files still a major problem? What is the current major RP
> problem?
STL files are a problem, but not a major one IMHO. The problems I see
are: inverted normals, unconnected facets and extreme file sizes. We
use five systems to generate STLs: Alias, ICEM Surf, CATIA, SolidWorks
and AutoCAD v14 (the majority being from CATIA). A good many of my
files are still from surface data (many parts still do not lend
themselves to solid modeling, i.e., body panels). As someone else said,
it is a training issue rather than a software issue. The unconnected
facets are almost always surfaces that have not been stitched together
and large file sizes are caused by too fine resolution (although the
native CATIA translator tends to make lage files anyway). I have no
idea what causes inverted normals (does anyone out there?)

> How do you repair your STL problems (3rd party software, CAD rework,
> service bureau, other)?
The majority of the the rework is done in either Magics or Imageware.
Inverted normals are generally a snap to fix -- just push a button. A
small number of unconnected facets can be repaired, but when it involves
poor CAD practice (unstitched contours/planes/etc) I have to send it
back to the CAD people for rework. Large files sizes are tough.
Although one can reduce the number of triangles, this almost always
takes away resolution from where you need it most. This size problem
mostly affects the LOM as it slices on the fly. We solved that here by
adding memory and a faster processor (64Mb & P133). The SLA preslices,
so the time spent is in Maestro and doesn't adversly effect the build.

> Do STL problems prevent your using RP effectively?
Not very often now that my CAD guys know what is needed to get good RP
parts. I had a 1/2 day seminar to show them the problems and offer
suggestions/solutions. It was quite effective.

> Does it cost, time, effort?
Time and effort (are they really different). Average repair time is 30
minutes, because we verify all files on Magics or I-ware. If I could
trust the STL file, I could save at least half of that. Slicing really
large files in Maestro is time consuming as is a simple thing like
transferring the files over the network.

If we were a service bureau, this would of course cost us (well, the
customer) money.

> If a service bureau repairs your they tell you, give you
> updated
> data?

> Can you use your CAD data on ANY RP system without problems? If no
> why?
I have no problems specific to CAD systems that I'm aware of (except as
outlined above).

> Which CAD systems produce the worst STL files?
See above.

> Has RP reached the limit of the STL file? Why?
I don't think so. The issue as stated before, is people, not
technology. It would be quite difficult to change input formats
(witness SLC from 3D), and simply not necessary as RP machines are not
accurate enough to need a "better" format. When we are able to create
tooling masters that do not require finishing, then the input format
will be the limiting factor.

> Dan Davis
> Division Head, RP&M
> Perusahaan Otomobil Nasional Berhad (PROTON)
Hicom Industrial Estate
Batu 3 PO Box 7100
Shah Alam, Selangor D. E.
> +60 3 511-1055
> +60 3 515-2380 direct fax

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