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Basic Concepts of Creating Shells | 347
Basic Concepts of Creating Shells
Unlike other sketched or placed features, a shell feature is initially applied to
all the faces of your active part, instead of only those you select. It doesn’t
need parametric dimensions to control placement. A part can have only one
shell feature.
When you add a shell feature to a part, Mechanical Desktop creates new faces
by offsetting existing ones inside or outside of their original positions. You
can also choose the midplane option, which offsets faces by half the entered
value to one side and half to the other side.
Mechanical Desktop treats continuously tangent faces as a single face when
offsetting. This illustration shows the progression for adding a shell feature
to a part and then a thickness override to the cylindrical face. The faces tan-
gent to the cylindrical face are also offset in the operation.
You can change a shell feature in different ways. You can change the offset
type and offset values in the Shell Feature dialog box. If you choose to
exclude or reclaim faces, or change thickness overrides, you select faces on
your part. In both cases, to apply your modifications you must update the
part.
Adding Shell Features to Models
In this tutorial, you add a shell feature to the existing model of a clutch hous-
ing for a 250cc two-stroke engine. The shell feature requires an excluded face
and multiple thickness overrides.
You apply what you’ve learned in previous chapters about constrained
sketches and features to examine an existing part. You then add a shell fea-
ture to the part, later modifying it to suit your design requirements.