16
AutoCAD and Its Applications—Advanced
Copyright Goodheart-Willcox Co., Inc.
Like surface modeling, solid modeling represents the shape of objects, but it
also provides data related to the physical properties of the objects. Solid models can
be analyzed to determine mass, volume, moments of inertia, and centroid. A solid
model is not just a skin, it represents a solid object. Some third-party programs allow
you to perform fi nite element analysis (FEA) on the model. Solid model fi les can also
be exported for use in stereolithography, rapid prototyping, and 3D printing. These
processes can produce a plastic or polymer prototype for analysis and testing. This is
discussed in Chapter 14. In addition, solid models can be rendered. Most 3D objects
are created as solid models.
In AutoCAD, solid models can be created from primitives. Primitives are basic
shapes used as the foundation to create complex shapes. Some of these basic shapes
include boxes, cylinders, spheres, and cones. Detailed shapes and primitives can be
created using 3D mesh primitives, mesh modeling techniques, and surface modeling.
A 3D mesh object, which is a type of surface model, can have a free-fl owing shape
because the size of the mesh can be adjusted to achieve various levels of smoothness.
Mesh objects can be converted to solids for use in model construction. See Chapter 9
for a detailed discussion on 3D mesh modeling. Solid primitives also can be modifi ed
to create a fi nished product. See Figure 1-18.
Surface and solid models can be exported from AutoCAD for use in animation
and rendering software, such as Autodesk 3ds Max®. Rendered models can be used in
any number of presentation formats, including slide shows, black-and-white or color
prints, and animations recorded to video fi les. Surface and solid models can also be
used to create virtual worlds for entertainment and gaming applications.
3D Object Snaps 3D Object Snaps
The construction and editing of a 3D model can be more effi cient with the use of 3D
object snaps. These work in the same manner as the standard 2D object snaps and can be set
using the
3D Object Snap
tab of the
Drafting Settings
dialog box. If you use 3D object snaps,
turn on only those options you need to construct the object. See Figure 1-19.
The Vertex,
Midpoint on
edge,
Center of
face, Perpendicular, and
Nearest to face
3D
object snap modes should be familiar to you from your work in 2D. The
Knot
3D object
DSETTINGS
Type
DSETTINGS
DS
SE
DDRMODES
A
B
Figure 1-18.
A—The two
cylinders and
the box are solid
primitives. B—With
a couple of quick
modifications,
the large cylinder
becomes a shaft with
a machined keyway.