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Exploring Drafting
to the profi le to be drawn. For example, if you
are making a sketch that shows the front view
of a part, use the front (XY) sketch plane.
In parametric modeling, commands in
the software are typically referred to as tools.
Tools used to make sketches are similar to
drawing commands used in 2D CAD drafting.
Common sketch tools include the Line, Circle,
and Arc tools. The Line tool is used to create
straight and inclined lines. The Circle tool is
used to create circles. Circles can be drawn
by specifying a center point and radius or
by specifying three points on the perimeter.
Circles can also be drawn tangent to other
objects, such as lines and circles. The Arc tool
is used to create arcs. Methods for creating
arcs include specifying a center, start, and end
point, or a start point, end point, and a point
defi ning the radius. Arcs can also be drawn
tangent to other objects. Additional shapes,
such as rectangles, ellipses, polygons, and
splines, can be drawn by using the appropriate
sketch tool.
Modify tools are available when creating
a sketch. For example, you can move, rotate,
scale, mirror, trim, extend, or offset sketch
geometry. Tools are also available for creating
fi llets and chamfers. Modify tools are often
useful for making quick adjustments and
increasing productivity. For example, if you
are making a sketch of a symmetrical object,
draw half of it and use the Mirror sketch tool
to create the other half. A construction line
5. Repeat the previous steps to create
additional parts to be used in the assembly.
6. Construct an assembly model from the
individual parts. Mate the parts using the
appropriate assembly constraints.
7. Generate working drawings from the
assembly.
Creating Sketches
Creating sketches in parametric modeling
is similar to creating orthographic views, as
discussed in Chapter 9. A sketch is a 2D profi le
of an object, such as the front or top view of
the object. Therefore, the fi rst step in making a
sketch is to decide which profi le of the object
will be used for the sketch. This determines
how the part model will begin to take shape.
When making a sketch for the base feature of
an object, for example, the profi le is usually
one of the principal views of the object. This is
often the profi le that shows the basic contour
of the object. See Figure 7-26.
When starting a sketch, sketch mode is made
active and you are in the sketch environment.
Normally, a sketch defi ning the base feature
is made on one of three default sketch planes.
These are the front (XY), top (XZ), and right-
side (YZ) sketch planes. The point where the
three sketch planes intersect is the coordinate
system origin. The sketch plane you select
determines the orientation of the part that will
be modeled and should normally correspond
A B
Goodheart-Willcox Publisher
Figure 7-26. Constructing a part model in parametric modeling typically begins by identifying the base feature and
creating a 2D sketch. In this example, a sketch representing the front view is created. A—The sketch is made up of
lines, circles, and arcs and is created on the front plane. B—The base feature is created by extruding the sketch.
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