diff --git a/nhf/materials.py b/nhf/materials.py
index 863ee3e..6108dc1 100644
--- a/nhf/materials.py
+++ b/nhf/materials.py
@@ -15,6 +15,7 @@ class Role(Enum):
 
     # Parent and child components in a load bearing joint
     PARENT = _color('blue4', 0.6)
+    CASING = _color('dodgerblue3', 0.6)
     CHILD = _color('darkorange2', 0.6)
     DAMPING = _color('springgreen', 0.5)
     STRUCTURE = _color('gray', 0.4)
diff --git a/nhf/touhou/houjuu_nue/parts.py b/nhf/touhou/houjuu_nue/parts.py
index a3a5bfb..bdf458e 100644
--- a/nhf/touhou/houjuu_nue/parts.py
+++ b/nhf/touhou/houjuu_nue/parts.py
@@ -1,4 +1,5 @@
 from dataclasses import dataclass
+from typing import Optional, Tuple
 import cadquery as Cq
 from nhf import Role
 from nhf.build import Model, target
@@ -25,8 +26,12 @@ class DiskJoint(Model):
     spring_thickness: float = 1.3
     spring_height: float = 6.5
     spring_tail_length: float = 45.0
-    spring_angle: float = 90.0
-    spring_angle_shift: float = 0
+
+    # Spring angle at 0 degrees of movement
+    spring_angle: float = 30.0
+    # Angle at which the spring exerts no torque
+    spring_angle_neutral: float = 90.0
+    spring_angle_shift: float = 30
     wall_inset: float = 2.0
 
     # Angular span of movement
@@ -55,15 +60,22 @@ class DiskJoint(Model):
         )
 
     @property
-    def total_thickness(self):
+    def neutral_movement_angle(self) -> Optional[float]:
+        a = self.spring_angle_neutral - self.spring_angle
+        if 0 <= a and a <= self.movement_angle:
+            return a
+        return None
+
+    @property
+    def total_thickness(self) -> float:
         return self.housing_thickness * 2 + self.disk_thickness
 
     @property
-    def opening_span(self):
+    def opening_span(self) -> float:
         return self.movement_angle + self.tongue_span
 
     @property
-    def housing_upper_carve_offset(self):
+    def housing_upper_carve_offset(self) -> float:
         return self.housing_thickness + self.disk_thickness - self.spring_height
 
     @property
@@ -147,8 +159,7 @@ class DiskJoint(Model):
         result = result.cut(
             self
             .wall()
-            .mirror("XY")
-            .located(Cq.Location((0, 0, self.housing_thickness + self.disk_thickness)))
+            .located(Cq.Location((0, 0, self.disk_thickness - self.wall_inset)))
             #.rotate((0, 0, 0), (1, 0, 0), 180)
             #.located(Cq.Location((0, 0, self.disk_thickness + self.housing_thickness)))
         )
@@ -165,7 +176,7 @@ class DiskJoint(Model):
                 width=self.spring_thickness,
                 height=self.housing_thickness
             ).located(Cq.Location((0, self.radius_spring_internal, 0))))
-        ).rotate((0, 0, 0), (0, 0, 1), self.spring_angle - self.spring_angle_shift)
+        ).rotate((0, 0, 0), (0, 0, 1), 180 + self.spring_angle - self.spring_angle_shift)
         result = (
             Cq.Workplane('XY')
             .cylinder(
@@ -192,7 +203,8 @@ class DiskJoint(Model):
             result = result.union(tube)
         wall = (
             self.wall()
-            .rotate((0, 0, 0), (1, 0, 0), 180)
+            .rotate((0, 0, 0), (0, 0, 1), self.tongue_span)
+            .mirror("XY")
             .located(Cq.Location((0, 0, self.disk_thickness + self.housing_thickness + self.wall_inset)))
         )
         result = (
@@ -202,18 +214,47 @@ class DiskJoint(Model):
         )
         return result
 
+    def add_constraints(self,
+                        assembly: Cq.Assembly,
+                        housing_lower: str,
+                        housing_upper: str,
+                        disk: str,
+                        angle: Tuple[float, float, float] = (0, 0, 0),
+                        ) -> Cq.Assembly:
+        """
+        The angle supplied must be perpendicular to the disk normal.
+        """
+        (
+            assembly
+            .constrain(f"{disk}?mate_bot", f"{housing_lower}?mate", "Plane")
+            .constrain(f"{disk}?mate_top", f"{housing_upper}?mate", "Plane")
+            .constrain(f"{housing_lower}?dir", f"{housing_upper}?dir", "Axis")
+            .constrain(f"{disk}?dir", "FixedRotation", angle)
+        )
 
-    def assembly(self) -> Cq.Assembly:
+
+    def assembly(self, angle: Optional[float] = 0) -> Cq.Assembly:
+        if angle is None:
+            angle = self.movement_angle
+            if angle is None:
+                angle = 0
+        else:
+            assert 0 <= angle <= self.movement_angle
         result = (
             Cq.Assembly()
             .add(self.disk(), name="disk", color=Role.CHILD.color)
             .add(self.housing_lower(), name="housing_lower", color=Role.PARENT.color)
-            .add(self.housing_upper(), name="housing_upper", color=Role.PARENT.color)
-            .constrain("disk?mate_bot", "housing_lower?mate", "Plane")
-            .constrain("disk?mate_top", "housing_upper?mate", "Plane")
-            .solve()
+            .add(self.housing_upper(), name="housing_upper", color=Role.CASING.color)
+            .constrain("housing_lower", "Fixed")
         )
-        return result
+        self.add_constraints(
+            result,
+            housing_lower="housing_lower",
+            housing_upper="housing_upper",
+            disk="disk",
+            angle=(0, 0, angle),
+        )
+        return result.solve()
 
 if __name__ == '__main__':
     p = DiskJoint()
diff --git a/nhf/touhou/houjuu_nue/test.py b/nhf/touhou/houjuu_nue/test.py
index 2f610d5..c5a9d27 100644
--- a/nhf/touhou/houjuu_nue/test.py
+++ b/nhf/touhou/houjuu_nue/test.py
@@ -1,8 +1,24 @@
 import unittest
 import cadquery as Cq
 import nhf.touhou.houjuu_nue as M
+import nhf.touhou.houjuu_nue.parts as MP
 from nhf.checks import pairwise_intersection
 
+class TestDiskJoint(unittest.TestCase):
+
+    def test_collision_0(self):
+        j = MP.DiskJoint()
+        assembly = j.assembly(angle=0)
+        self.assertEqual(pairwise_intersection(assembly), [])
+    def test_collision_mid(self):
+        j = MP.DiskJoint()
+        assembly = j.assembly(angle=j.movement_angle / 2)
+        self.assertEqual(pairwise_intersection(assembly), [])
+    def test_collision_max(self):
+        j = MP.DiskJoint()
+        assembly = j.assembly(angle=j.movement_angle)
+        self.assertEqual(pairwise_intersection(assembly), [])
+
 class Test(unittest.TestCase):
 
     def test_hs_joint_parent(self):