Part Modeling > Engineering Features > Shell > Restrictions on Creating Shell Features
Restrictions on Creating Shell Features
Note the following restrictions on creating Shell features:
If the part has a corner between more than three surfaces, the Shell feature may be geometrically undefined. In this case, the problem area is highlighted. The surface to be removed must be surrounded by edges (a fully revolved surface of revolution is not valid), and the surfaces that intersect the edge must form an angle through the solid geometry of less than 180°. As long as this condition is met, you can select any sculpted surfaces as the surface to be removed.
Surfaces selected in a collector cannot be selected in any other collector. For example, if you select a surface in the Removed surfaces collector, then you cannot select the same surface in the Non-default thickness collector or the Excluded surfaces collector.