174
Exploring Drafting
but it is free to translate (move) through the
hole with the screw subassembly.
Drawing Documentation
Part and assembly drawings are created
by inserting drawing views generated by
the software. Parametric modeling programs
typically provide tools for generating common
types of drawing views, such as orthographic
views. Drawings can be created at any time
during the modeling process. Typically,
drawings are created from parts, subassemblies,
and the top-level assembly for use in manu-
facturing. As previously discussed, drawings
are created as separate drawing fi les. A
drawing fi le is linked to the corresponding part
or assembly fi le and updates automatically if
the part or assembly is edited.
Creating Part and Assembly
Drawings
In order to create a part or assembly
drawing, some setup steps are required. It is
often useful to start a new drawing fi le using
a template. A drawing template contains user-
defi ned settings and a standard layout format,
including a title block and border. Most
programs provide predefi ned templates, but
custom templates can be created for specifi c
uses. For example, it may be necessary to create
For example, a grinding wheel can be
constrained so that it is allowed to rotate about
the appropriate axis, but all other degrees of
freedom are removed.
Assembly constraints are commonly referred
to as mates because they are used to align or
“mate” parts together. They can be used to
align parts face-to-face, along the same center
axis, or at an angle. Assembly constraints
are similar to geometric constraints used in
sketches. For example, a perpendicular assembly
constraint can be used to constrain a face of
a part so that it remains perpendicular to the
face of another part. Other types of assembly
constraints include the parallel, tangent,
concentric, coincident, distance, and angle
constraints.
Figure 7-33 shows a mechanical assembly of
a C-clamp. The components of the assembly
include the clamp body, the screw subassembly
shown in Figure 7-32, and a cap at the end of
the screw subassembly. The clamp body is the
fi rst component placed in the assembly and is
fully constrained (all degrees of freedom are
removed). The screw subassembly is assembled
prior to being mated to the clamp body. The
screw subassembly is constrained so that it
remains concentric to the hole in the clamp
body, but it is free to rotate about its axis and
translate (move) through the hole. The cap is
mated to the end of the screw subassembly
with concentric and coincident constraints,
Goodheart-Willcox Publisher
Figure 7-33. A C-clamp assembly made up of a clamp body, a screw subassembly, and an end cap. Each part is
positioned accurately and constrained to remove the appropriate degrees of freedom.
Copyright Goodheart-Willcox Co., Inc.