AutoCAD and Its Applications—Comprehensive 2013, 20th Edition Page 1087 (1089 of 1650)

Chapter 1 Introduction to Three-Dimensional Modeling
31
Figure 1-18.
A—These 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.
A
B
Figure 1-19.
The 3D object snaps
can be set in the
Drafting Settings
dialog box.
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 files. Surface and solid models can also be fi
used to create virtual worlds for entertainment and gaming applications.
3D Object Snaps 3D Object Snaps
with the use ficient
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.
DSETTINGS
Type
DSETTINGS
DS
SE
DDRMODES

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Chapter 1 Introduction to Three-Dimensional Modeling
31
Figure 1-18.
A—These 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.
A
B
Figure 1-19.
The 3D object snaps
can be set in the
Drafting Settings
dialog box.
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 files. Surface and solid models can also be fi
used to create virtual worlds for entertainment and gaming applications.
3D Object Snaps 3D Object Snaps
with the use ficient
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.
DSETTINGS
Type
DSETTINGS
DS
SE
DDRMODES

Help

30
AutoCAD and Its Applications—Advanced
Exercise 1-5
Complete the exercise on the companion website.
www.g-wlearning.com/CAD
3D Construction Techniques 3D Construction Techniques
Before constructing a 3D model, you should determine the purpose of your
design. What will the model be used for—manufacturing, analysis, or presentation?
This helps you determine which tools you should use to construct and display the
model. Three-dimensional objects can be drawn as solids, meshes, or surfaces and
displayed in wireframe, hidden-line removed, and shaded views.
A wireframe object, or model, is an object constructed of lines in 3D space. t
Wireframe models are hard to visualize because it is diffi to determine the angle ficult
of view and the nature of the surfaces represented by the lines. The
HIDE
command
has no effect on a true wireframe model because there is nothing to hide. All lines are
always visible because there are no surfaces or faces between the lines. True wireframe
models have very limited applications.
Surface modeling represents solid objects by creating a skin in the shape of the g
object. However, there is nothing inside of the object. Think of a surface model as a
balloon filled with air. A surface model looks more like the real object than a wire- fi
frame and can be used for rendering. Surface models are often constructed for applica-
tions such as civil engineering terrain modeling, automobile body design, sheet metal
design and fabrication, and animation. Surface modeling techniques are discussed in
Chapter 10.
Like surface modeling, solid modeling represents the shape of objects, but it also g
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 finite element analysis (FEA) on the model. Solid model files fi can also be fi
exported for use in stereolithography and rapid prototyping. These processes can
render 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-flowing t shape fl
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 modifiedfi
to create a fi nished product. See fi Figure 1-18.
NOTE OT TE
If the image is rendered in the viewport, clean the screen using the
ZOOM, PAN, REGEN, or
REDRAW
command. Setting the rendering
destination as the viewport is discussed in Chapter 15.

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32
AutoCAD and Its Applications—Advanced
There are six 3D object snaps. With the exception of the knot snap, these should
be familiar to you from your work in 2D. The knot 3D object snap option refers to a fit fi
curve spline and the point at which one curve ends and the next curve begins.
The 3D AutoSnap markers that appear when drawing can be displayed in a
different color than 2D AutoSnap markers. Set the color for 3D AutoSnap markers by
accessing the
Display
tab in the
Options
dialog box. Pick the
Colors…
button in the
Window Elements
area to access the
Drawing Window Colors
dialog box. Select the
desired context in the
Context:
list and then select a color for the
3d Autosnap marker
element in the
Interface element:
list. Drawing window customization is covered in
detail in AutoCAD and Its Applications—Customization and Programming.g g
Sample 3D Construction Sample 3D Construction
The example provided here illustrates how you can move from a layout sketch to
an exact 2D drawing with parametric constraints, then quickly extrude the object into
a 3D solid model. Techniques illustrated here are discussed throughout the book. The
object shown is the plastic housing for a 24/15-pin cable connector. The final rendition fi
of this object would include internal cutouts, rounded edges, and holes, but are not
shown in this example.
Creating a 2D Sketch
A 2D layout can be drawn quickly using the
Drafting & Annotation
workspace. In
doing so, you can create a quick sketch without close attention to exact dimensions
or you can use direct distance entry and polar tracking for accuracy. If appropriate,
constraints can then be used to apply accurate dimensions and geometric relation-
ships, such as perpendicularity and parallelism, to the object. See Figure 1-20A. In this
example, only half of the object is drawn, since it is symmetrical. Then the
MIRROR
command is used to complete the layout. See Figure 1-20B.
Converting to a Region
The object is still composed of just 2D lines. Therefore, it must be changed to an
object that can be converted into a solid model. The
REGION
command is used for this
purpose. After selecting this command, you are prompted to select objects. Be sure to
Application Menu
Options
Type
OPTIONS
OP
OPTIONS
Figure 1-20.
A—Half of the 2D object is drawn using geometric constraints. B—The object is mirrored to
create a full profile of the connector body. C—The object is now a “region” and is displayed
in the southwest isometric viewpoint.
B
A C
REGION
Ribbon
Home
Draw
Region
Type
REGION
REG

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