I've had very bad experiences with parts from Autocad - any version.
This has been true even when the part was really very simple. Even on
the rare occasion when an Autocad file is buildable, they're full of
little holes when you look closely. Cadkey is almost as bad as Autocad,
but seems to be able to handle very simple parts a little better.
My best experiences have been with Pro/E and SDRC, but SDRC has a
tendency to "braid" small rounds, which makes them difficult to
accurately finish. This effect is strongly scale related - rounds of
slightly different radius on the same part have a different quality of
faceting. Unigraphics files are usually pretty good, especially when
created by a skilled user.
Many problems are addresable in the better syustems be increasing facet
resolution, but at the cost of excessive slice times. Angle control
variations don't do a lot in Pro/E, but sometimes help in SDRC. It's
important to educate users that making an STL look great in a viewer is
irrelevant once you drop below the resolution of the process - you're
only aggrivating the RP machine operator. In extreme cases, you're
hurting yourself, because you're stealing time (in slicing and viewing
huge files) that the machine operator might have used to make better
choices in orientation, supports, or the dividing of large parts for
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
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