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Constraining Sketches | 87
The ways a sketch can change size or shape are called degrees of freedom. For
example, a circle has two degrees of freedom—the location of its center and
its radius. If the center and radius are defined, the circle is fully constrained
and those values can be maintained.
Similarly, an arc has four degrees of freedom—center, radius, and the end-
points of the arc segment.
The degrees of freedom you define correspond to how fully the sketch is con-
strained. If you define all degrees of freedom, the arc is fully constrained. If you
do not define all degrees of freedom, the sketch is underconstrained.
Mechanical Desktop does not allow you to define a degree of freedom in
more than one way and thus prevents you from overconstraining a sketch.
Before you add constraints, study your sketch, and then decide how to con-
strain it. Usually, you need both geometric constraints and dimensions. See
“Constraining Tips” on page 86.
You should fully constrain sketches so that they update predictably as you
make changes. As you gain experience, you may want to underconstrain a
sketch while you work out fine points of a design, but doing so may allow
that feature to become distorted as you modify dimensions or constraints.
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