Graphics Reference
In-Depth Information
After clients submit their design ile John's next step is to convert the ile
into a special format for 3D printing called STL. STL is an industry-standard,
decades-old ile format that was originally created by Chuck Hull, the inventor
of SL printing and founder of 3D Systems. The STL ile format is somewhat
analogous to the PostScript ile format that translates computer documents
into something a 2D paper printer can read and work with.
“A big part of my job is quality control to make sure that the STL ile is
going to be able to do what it's supposed to,” said John. Today's STL ile format
harkens back to an era when people asked much less of their 3D printers. The
job of the STL ile isn't an easy one. The STL format has had a long and distin-
guished life but it simply can't keep up with advances in printing technology
and design software.
The challenge lies in the fact that the STL ile must somehow translate
design complexities and intricate details that may be straightforward in digital
form, but can be dificult to convey to a 3D print head. For example, engineer-
ing software grew up in the era of manufacturing machines that cut objects
rather than made them out of layers. Therefore, relecting its manufacturing
lineage, engineering design software is still learning how to think in additive
rather than subtractive operations.
After a design ile has been converted to STL, the STL “wraps” the design
object's digital “shape” inside a virtual surface, called a mesh, that's made up of
thousands (or sometimes millions) of interlocked polygons. Each interlocked
polygon (triangles are frequently used) in the surface mesh holds information
about an object's shape. Somewhat confusing to non-engineers, in a design
ile conversion, anything designated as a surface includes any portion of the
designed object that touches air. For example, a design object's surface can be
on the outside of a designed object, or in its hollow interior.
When the STL conversion is complete, the virtual surface of the newly
wrapped STL ile must be watertight, somewhat similar to the process of coat-
ing a physical object in some kind of waterprooing sealant. A watertight STL
ile is one whose surface mesh accurately and completely covers and captures
the design object's surfaces curves and interior hollows. Like a hole or gap in
a sealed and waterproofed pair of suede shoes, gaps in an STL ile's surface
mesh will cause problems later down the road.
Once the STL ile is watertight and ready to go, the bridge connecting
CAD and CAM is nearly complete. The object to be 3D printed, now snuggly
wrapped in a watertight surface mesh, must be prepared for its inal phase:
the layered fabrication process. At this point, the STL ile does its inal bit of
 
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