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Glossary 143
OBJ file
The OBJ file format is an open format for representing 3D
geometry of objects. It does not include features such as
color or texture, nor does it specify a fixed size; it solely
represents the shape. However, OBJ files can have a com-
panion MTL file, where the MTL file stores properties such
as color and texture. OBJ file format is an open format,
first developed by Wavefront Technologies, and now used
by other 3D graphics applications, including 3D printing.
OBJ files are very commonly used for 3D art, design, and
graphics in general, but
.stl
files are more commonly used
in the specific arena of 3D printing, as
.stl
files are some-
what simpler, and more easily correctable. Note that as
OBJ files often were not created with 3D printing in mind,
models in OBJ format frequently are less “ready to print”
than a typical
.stl
file might be. Some lovely OBJ for-
mat models may not be suitable for 3D printing; others,
though printable, may require some adjustment of orienta-
tion (
ROTATE
), size (
SCALE
), and position (
MOVE
) prior to
printing. 61 , See also CAD , MTL file &
.stl
file
over-extrusion
When the extruder outputs a surplus of plastic, over-ex-
trusion results. Over and under-extrusion are caused by a
mismatch between the slicer’s expectations and reality: the
slicer expects that when a millimeter of raw filament is fed
into the extruder, a specific volume
V
e
of plastic will then
be extruded — output by the extruder. When the actual
volume of plastic output,
V
a
, exceeds V
e
, over-extrusion re-
sults; when V
a
is less than V
e
, under-extrusion results.