Fully closed shelling

cadquery/cq.py

@@ -1118,8 +1118,6 @@ def shell(self, thickness: float) -> "Workplane":
         solidRef = self.findSolid()
 
         faces = [f for f in self.objects if isinstance(f, Face)]
-        if len(faces) < len(self.objects):
-            raise ValueError("Shelling requires that faces are selected")
 
         s = solidRef.shell(faces, thickness)
         return self.newObject([s])

cadquery/occ_impl/shapes.py

@@ -10,7 +10,6 @@
     Any,
     overload,
     TypeVar,
-    Callable,
     cast as tcast,
 )
 from typing_extensions import Literal, Protocol
@@ -51,6 +50,7 @@
     BRepBuilderAPI_Transformed,
     BRepBuilderAPI_RightCorner,
     BRepBuilderAPI_RoundCorner,
+    BRepBuilderAPI_MakeSolid,
 )
 
 # properties used to store mass calculation result
@@ -158,10 +158,9 @@
 
 from OCP.IFSelect import IFSelect_ReturnStatus
 
-from OCP.TopAbs import TopAbs_ShapeEnum
+from OCP.TopAbs import TopAbs_ShapeEnum, TopAbs_Orientation
 
 from math import pi, sqrt
-from functools import reduce
 import warnings
 
 TOLERANCE = 1e-6
@@ -1563,16 +1562,35 @@ def shell(
         """
 
         occ_faces_list = TopTools_ListOfShape()
-        for f in faceList:
-            occ_faces_list.Append(f.wrapped)
 
-        shell_builder = BRepOffsetAPI_MakeThickSolid(
-            self.wrapped, occ_faces_list, thickness, tolerance
-        )
+        if faceList:
+            for f in faceList:
+                occ_faces_list.Append(f.wrapped)
+
+            shell_builder = BRepOffsetAPI_MakeThickSolid(
+                self.wrapped, occ_faces_list, thickness, tolerance
+            )
+
+            shell_builder.Build()
+            rv = shell_builder.Shape()
 
-        shell_builder.Build()
+        else:  # if no faces provided a watertight solid will be constructed
+            shell_builder = BRepOffsetAPI_MakeThickSolid(
+                self.wrapped, occ_faces_list, thickness, tolerance
+            )
+
+            shell_builder.Build()
+            s1 = self.__class__(shell_builder.Shape()).Shells()[0].wrapped
+            s2 = self.Shells()[0].wrapped
+
+            # s1 can be outer or inner shell depending on the thickness sign
+            if thickness > 0:
+                rv = BRepBuilderAPI_MakeSolid(s1, s2).Shape()
+            else:
+                rv = BRepBuilderAPI_MakeSolid(s2, s1).Shape()
 
-        return self.__class__(shell_builder.Shape())
+        # fix needed for the orientations
+        return self.__class__(rv) if faceList else self.__class__(rv).fix()
 
     def isInside(
         self: ShapeProtocol, point: VectorLike, tolerance: float = 1.0e-6

tests/test_cadquery.py

@@ -1816,6 +1816,18 @@ def testSimpleShell(self):
         self.saveModel(s)
         self.assertEqual(23, s.faces().size())
 
+    def testClosedShell(self):
+        """
+            Create a hollow box
+        """
+        s1 = Workplane("XY").box(2, 2, 2).shell(-0.1)
+        self.assertEqual(12, s1.faces().size())
+        self.assertTrue(s1.val().isValid())
+
+        s2 = Workplane("XY").box(2, 2, 2).shell(0.1)
+        self.assertEqual(32, s2.faces().size())
+        self.assertTrue(s2.val().isValid())
+
     def testOpenCornerShell(self):
         s = Workplane("XY").box(1, 1, 1)
         s1 = s.faces("+Z")