New Eiki crown design using conformal mapping

nhf/touhou/shiki_eiki/crown.py

@@ -357,6 +357,10 @@ class Crown(Model):
         return sketch.assemble()
 
     def side_guard(self) -> Cq.Workplane:
+        """
+        Constructs the side guard using a cone. Via Gauss's Theorema Egregium,
+        the surface of the cone can be deformed into a plane.
+        """
         angle = 360 / 5
         outer = Cq.Solid.makeCone(
             radius1=self.radius_lower + self.side_guard_thickness,
@@ -399,7 +403,48 @@ class Crown(Model):
         )
         return shell * profile - channel
 
+    def front_surrogate(self) -> Cq.Workplane:
+        """
+        Create a surrogate cylindrical section structure for the front since we
+        cannot bend extrusions
+        """
+        angle = 360 / 5
+        outer = Cq.Solid.makeCone(
+            radius1=self.radius_lower + self.thickness,
+            radius2=self.radius_upper + self.thickness,
+            height=self.height,
+            angleDegrees=angle,
+        )
+        inner = Cq.Solid.makeCone(
+            radius1=self.radius_lower,
+            radius2=self.radius_upper,
+            height=self.height,
+            angleDegrees=angle,
+        )
+        shell = (
+            outer.cut(inner)
+            .rotate((0,0,0), (0,0,1), -angle/2)
+        )
+        dx = math.sin(math.radians(angle / 2)) * self.radius_middle
+        profile = (
+            Cq.Workplane('YZ')
+            .polyline([
+                (0, self.height),
+                (-dx, self.height / 2),
+                (-dx, 0),
+                (dx, 0),
+                (dx, self.height / 2),
+            ])
+            .close()
+            .extrude(self.radius_upper + self.side_guard_thickness)
+            .val()
+        )
+        return shell * profile
+
     def assembly(self) -> Cq.Assembly:
+        """
+        New assembly using conformal mapping on the cone.
+        """
         side_guard = self.side_guard()
         a = Cq.Assembly()
         for i in range(1,5):
@@ -409,6 +454,11 @@ class Crown(Model):
                 material=self.material_side,
                 loc=Cq.Location(rz=i*360/5)
             )
+        a.addS(
+            self.front_surrogate(),
+            name="front",
+            material=self.material,
+        )
         return a
 
     def old_assembly(self) -> Cq.Assembly: