Sheetmetal > Designing in Sheetmetal Design > Using Forms > Forms with Hollows
  
Forms with Hollows
Your form can contain a combination of convex and concave geometry, creating hollows. The hollows in the form must not drop below the base plane or mating surface, meaning all the form geometry must be on the same side of the base plane.
 
* Make sure that the distance between the hollow surface and the outer surface allows for the material thickness of the sheet metal.
Form Reference Part
Allow for Material Thickness
1. Allowance for the sheet metal material thickness