diff --git a/nhf/materials.py b/nhf/materials.py
index 9408164..f87b796 100644
--- a/nhf/materials.py
+++ b/nhf/materials.py
@@ -43,7 +43,7 @@ ROLE_COLOR_MAP = {
     Role.PARENT:     _color('blue4', 0.6),
     Role.CASING:     _color('dodgerblue3', 0.6),
     Role.CHILD:      _color('darkorange2', 0.6),
-    Role.DAMPING:    _color('springgreen', 0.8),
+    Role.DAMPING:    _color('springgreen', 1.0),
     Role.STRUCTURE:  _color('gray', 0.4),
     Role.DECORATION: _color('lightseagreen', 0.4),
     Role.ELECTRONIC: _color('mediumorchid', 0.5),
diff --git a/nhf/parts/joints.py b/nhf/parts/joints.py
index 3ff76e9..594c2cb 100644
--- a/nhf/parts/joints.py
+++ b/nhf/parts/joints.py
@@ -1,8 +1,8 @@
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from typing import Optional
 import math
 import cadquery as Cq
-import nhf.parts.springs as springs
+from nhf.parts.springs import TorsionSpring
 from nhf import Role
 import nhf.utils
 
@@ -158,99 +158,6 @@ class HirthJoint:
             offset=offset)
         return result.solve()
 
-def comma_joint(radius=30,
-                shaft_radius=10,
-                height=10,
-                flange=10,
-                flange_thickness=25,
-                n_serration=16,
-                serration_angle_offset=0,
-                serration_height=5,
-                serration_inner_radius=20,
-                serration_theta=2 * math.pi / 48,
-                serration_tilt=-30,
-                right_handed=False):
-    """
-    Produces a "o_" shaped joint, with serrations to accomodate a torsion spring
-    """
-    assert flange_thickness <= radius
-    flange_poly = [
-        (0, radius - flange_thickness),
-        (0, radius),
-        (flange + radius, radius),
-        (flange + radius, radius - flange_thickness)
-    ]
-    if right_handed:
-        flange_poly = [(x, -y) for x,y in flange_poly]
-    sketch = (
-        Cq.Sketch()
-        .circle(radius)
-        .polygon(flange_poly, mode='a')
-        .circle(shaft_radius, mode='s')
-    )
-    serration_poly = [
-        (0, 0), (radius, 0),
-        (radius, radius * math.tan(serration_theta))
-    ]
-    serration = (
-        Cq.Workplane('XY')
-        .sketch()
-        .polygon(serration_poly)
-        .circle(radius, mode='i')
-        .circle(serration_inner_radius, mode='s')
-        .finalize()
-        .extrude(serration_height)
-        .translate(Cq.Vector((-serration_inner_radius, 0, height)))
-        .rotate(
-            axisStartPoint=(0, 0, 0),
-            axisEndPoint=(0, 0, height),
-            angleDegrees=serration_tilt)
-        .val()
-    )
-    serrations = (
-        Cq.Workplane('XY')
-        .polarArray(radius=serration_inner_radius,
-                    startAngle=0+serration_angle_offset,
-                    angle=360+serration_angle_offset,
-                    count=n_serration)
-        .eachpoint(lambda loc: serration.located(loc))
-    )
-    result = (
-        Cq.Workplane()
-        .add(sketch)
-        .extrude(height)
-        .union(serrations)
-        .clean()
-    )
-
-    result.polyline([
-        (0, 0, height - serration_height),
-        (0, 0, height + serration_height)],
-        forConstruction=True).tag("serrated")
-    result.polyline([
-        (0, radius, 0),
-        (flange + radius, radius, 0)],
-        forConstruction=True).tag("tail")
-    result.faces('>X').tag("tail_end")
-    return result
-
-def comma_assembly():
-    joint1 = comma_joint()
-    joint2 = comma_joint()
-    spring = springs.torsion_spring()
-    result = (
-        Cq.Assembly()
-        .add(joint1, name="joint1", color=Cq.Color(0.8,0.8,0.5,0.3))
-        .add(joint2, name="joint2", color=Cq.Color(0.8,0.8,0.5,0.3))
-        .add(spring, name="spring", color=Cq.Color(0.5,0.5,0.5,1))
-        .constrain("joint1?serrated", "spring?bot", "Plane")
-        .constrain("joint2?serrated", "spring?top", "Plane")
-        .constrain("joint1?tail", "FixedAxis", (1, 0, 0))
-        .constrain("joint2?tail", "FixedAxis", (-1, 0, 0))
-        .solve()
-    )
-    return result
-
 @dataclass
 class TorsionJoint:
     """
@@ -268,6 +175,13 @@ class TorsionJoint:
     2. A slotted annular extrusion where the slot allows the spring to rest
     3. An outer and an inner annuli which forms a track the rider can move on
     """
+    spring: TorsionSpring = field(default_factory=lambda: TorsionSpring(
+        radius=10.0,
+        thickness=2.0,
+        height=15.0,
+        tail_length=35.0,
+        right_handed=False,
+    ))
 
     # Radius limit for rotating components
     radius_track: float = 40
@@ -275,7 +189,6 @@ class TorsionJoint:
     track_disk_height: float = 10
     rider_disk_height: float = 8
 
-    radius_spring: float = 15
     radius_axle: float = 6
 
     # If true, cover the spring hole. May make it difficult to insert the spring
@@ -283,12 +196,6 @@ class TorsionJoint:
     spring_hole_cover_track: bool = False
     spring_hole_cover_rider: bool = False
 
-    # Also used for the height of the hole for the spring
-    spring_thickness: float = 2
-    spring_height: float = 15
-
-    spring_tail_length: float = 35
-
     groove_radius_outer: float = 35
     groove_radius_inner: float = 20
     # Gap on inner groove to ease movement
@@ -301,23 +208,19 @@ class TorsionJoint:
     rider_slot_begin: float = 0
     rider_slot_span: float = 90
 
-    right_handed: bool = False
-
 
     def __post_init__(self):
         assert self.radius_track > self.groove_radius_outer
-        assert self.radius_rider > self.groove_radius_outer
-        assert self.groove_radius_outer > self.groove_radius_inner + self.groove_inner_gap
-        assert self.groove_radius_inner > self.radius_spring
-        assert self.spring_height > self.groove_depth, "Groove is too deep"
-        assert self.radius_spring > self.radius_axle
+        assert self.radius_rider > self.groove_radius_outer > self.groove_radius_inner + self.groove_inner_gap
+        assert self.groove_radius_inner > self.spring.radius > self.radius_axle
+        assert self.spring.height > self.groove_depth, "Groove is too deep"
 
     @property
     def total_height(self):
         """
         Total height counting from bottom to top
         """
-        return self.track_disk_height + self.rider_disk_height + self.spring_height
+        return self.track_disk_height + self.rider_disk_height + self.spring.height
 
     @property
     def radius(self):
@@ -326,28 +229,24 @@ class TorsionJoint:
         """
         return max(self.radius_rider, self.radius_track)
 
-    @property
-    def _radius_spring_internal(self):
-        return self.radius_spring - self.spring_thickness
-
     def _slot_polygon(self, flip: bool=False):
-        r1 = self.radius_spring - self.spring_thickness
-        r2 = self.radius_spring
-        flip = flip != self.right_handed
+        r1 = self.spring.radius_inner
+        r2 = self.spring.radius
+        flip = flip != self.spring.right_handed
         if flip:
             r1 = -r1
             r2 = -r2
         return [
             (0, r2),
-            (self.spring_tail_length, r2),
-            (self.spring_tail_length, r1),
+            (self.spring.tail_length, r2),
+            (self.spring.tail_length, r1),
             (0, r1),
         ]
     def _directrix(self, height, theta=0):
         c, s = math.cos(theta), math.sin(theta)
-        r2 = self.radius_spring
-        l = self.spring_tail_length
-        if self.right_handed:
+        r2 = self.spring.radius
+        l = self.spring.tail_length
+        if self.spring.right_handed:
             r2 = -r2
         # This is (0, r2) and (l, r2) transformed by right handed rotation
         # matrix `[[c, -s], [s, c]]`
@@ -356,16 +255,6 @@ class TorsionJoint:
             (c * l - s * r2, s * l + c * r2, height),
         ]
 
-
-    def spring(self):
-        return springs.torsion_spring(
-            radius=self.radius_spring,
-            height=self.spring_height,
-            thickness=self.spring_thickness,
-            tail_length=self.spring_tail_length,
-            right_handed=self.right_handed,
-        )
-
     def track(self):
         # TODO: Cover outer part of track only. Can we do this?
         groove_profile = (
@@ -373,14 +262,14 @@ class TorsionJoint:
             .circle(self.radius_track)
             .circle(self.groove_radius_outer, mode='s')
             .circle(self.groove_radius_inner, mode='a')
-            .circle(self.radius_spring, mode='s')
+            .circle(self.spring.radius, mode='s')
         )
         spring_hole_profile = (
             Cq.Sketch()
             .circle(self.radius_track)
-            .circle(self.radius_spring, mode='s')
+            .circle(self.spring.radius, mode='s')
         )
-        slot_height = self.spring_thickness
+        slot_height = self.spring.thickness
         if not self.spring_hole_cover_track:
             slot_height += self.groove_depth
         slot = (
@@ -400,7 +289,7 @@ class TorsionJoint:
             .faces('>Z')
             .tag("spring")
             .placeSketch(spring_hole_profile)
-            .extrude(self.spring_thickness)
+            .extrude(self.spring.thickness)
             # If the spring hole profile is not simply connected, this workplane
             # will have to be created from the `spring-mate` face.
             .faces('>Z')
@@ -425,7 +314,7 @@ class TorsionJoint:
         wall_profile = (
             Cq.Sketch()
             .circle(self.radius_rider, mode='a')
-            .circle(self.radius_spring, mode='s')
+            .circle(self.spring.radius, mode='s')
             .parray(
                 r=0,
                 a1=rider_slot_begin,
@@ -451,7 +340,7 @@ class TorsionJoint:
                 .reset()
             )
             #.circle(self._radius_wall, mode='a')
-        middle_height = self.spring_height - self.groove_depth - self.rider_gap - self.spring_thickness
+        middle_height = self.spring.height - self.groove_depth - self.rider_gap - self.spring.thickness
         result = (
             Cq.Workplane('XY')
             .cylinder(
@@ -471,8 +360,8 @@ class TorsionJoint:
             .extrude(self.groove_depth + self.rider_gap)
             .faces(tag="spring")
             .workplane()
-            .circle(self._radius_spring_internal)
-            .extrude(self.spring_height)
+            .circle(self.spring.radius_inner)
+            .extrude(self.spring.height)
             .faces("<Z")
             .workplane()
             .hole(self.radius_axle * 2)
@@ -490,10 +379,10 @@ class TorsionJoint:
                             forConstruction=True).tag(f"dir{j}")
         return result
 
-    def rider_track_assembly(self, directrix=0):
+    def rider_track_assembly(self, directrix: int = 0, deflection: float = 0):
         rider = self.rider()
         track = self.track()
-        spring = self.spring()
+        spring = self.spring.generate(deflection=deflection)
         result = (
             Cq.Assembly()
             .addS(spring, name="spring", role=Role.DAMPING)
diff --git a/nhf/parts/springs.py b/nhf/parts/springs.py
index c695d23..80c1915 100644
--- a/nhf/parts/springs.py
+++ b/nhf/parts/springs.py
@@ -1,59 +1,75 @@
 import math
+from typing import Optional
+from dataclasses import dataclass
 import cadquery as Cq
 
-def torsion_spring(radius=12,
-                   height=20,
-                   thickness=2,
-                   omega=90,
-                   tail_length=25,
-                   right_handed: bool = False):
+@dataclass
+class TorsionSpring:
     """
-    Produces a torsion spring with abridged geometry since sweep is very slow in
-    cq-editor.
+    A torsion spring with abridged geometry (since sweep is slow)
     """
-    if right_handed:
-        omega = -omega
-    base = (
-        Cq.Workplane('XY')
-        .cylinder(height=height, radius=radius,
-                  centered=(True, True, False))
-    )
-    base.faces(">Z").tag("top")
-    base.faces("<Z").tag("bot")
+    # Outer radius
+    radius: float = 12.0
+    height: float = 20.0
+    thickness: float = 2.0
 
-    box_shift = -radius if right_handed else radius-thickness
-    result = (
-        base
-        .cylinder(height=height, radius=radius - thickness, combine='s',
-                  centered=(True, True, True))
-        .transformed(
-            offset=(0, box_shift),
-            rotate=(0, 0, 0))
-        .box(
-            length=tail_length,
-            width=thickness,
-            height=thickness,
-            centered=False)
-        .copyWorkplane(Cq.Workplane('XY'))
-        .transformed(
-            offset=(0, 0, height - thickness),
-            rotate=(0, 0, omega))
-        .center(-tail_length, box_shift)
-        .box(
-            length=tail_length,
-            width=thickness,
-            height=thickness,
-            centered=False)
-    )
-    r = -radius if right_handed else radius
-    plane = result.copyWorkplane(Cq.Workplane('XY'))
-    plane.polyline([(0, r, 0), (tail_length, r, 0)],
-                   forConstruction=True).tag("dir_bot")
-    omega = math.radians(omega)
-    c, s = math.cos(omega), math.sin(omega)
-    l = -tail_length
-    plane.polyline([
-        (-s * r,        c * r, height),
-        (c * l - s * r, c * r + s * l, height)],
-        forConstruction=True).tag("dir_top")
-    return result
+    # Angle (in degrees) between the two legs at neutral position
+    angle_neutral: float = 90.0
+
+    tail_length: float = 25.0
+    right_handed: bool = False
+
+    torsion_rate: Optional[float] = None
+
+    @property
+    def radius_inner(self) -> float:
+        return self.radius - self.thickness
+
+    def torque_at(self, theta: float) -> float:
+        return self.torsion_rate * theta
+
+    def generate(self, deflection: float = 0):
+        omega = self.angle_neutral + deflection
+        omega = -omega if self.right_handed else omega
+        base = (
+            Cq.Workplane('XY')
+            .cylinder(height=self.height, radius=self.radius,
+                      centered=(True, True, False))
+        )
+        base.faces(">Z").tag("top")
+        base.faces("<Z").tag("bot")
+
+        box_shift = -self.radius if self.right_handed else self.radius-self.thickness
+        tail = Cq.Solid.makeCylinder(
+            height=self.tail_length,
+            radius=self.thickness / 2)
+        # points cylinder to +X
+        dy = self.radius - self.thickness / 2
+        if self.right_handed:
+            dy = -dy
+        loc_dir_x = Cq.Location((0, 0, self.thickness / 2), (0, 1, 0), 90)
+        loc_shift = Cq.Location((0, dy, 0))
+        loc_top = Cq.Location((0, 0, self.height - self.thickness), (0, 0, 1), omega + 180)
+        result = (
+            base
+            .cylinder(
+                height=self.height,
+                radius=self.radius - self.thickness,
+                combine='s',
+                centered=(True, True, True))
+            .union(tail.located(loc_shift * loc_dir_x))
+            .union(tail.located(loc_top * loc_shift.inverse * loc_dir_x))
+            .clean()
+        )
+        r = -self.radius if self.right_handed else self.radius
+        plane = result.copyWorkplane(Cq.Workplane('XY'))
+        plane.polyline([(0, r, 0), (self.tail_length, r, 0)],
+                       forConstruction=True).tag("dir_bot")
+        omega = math.radians(omega)
+        c, s = math.cos(omega), math.sin(omega)
+        l = -self.tail_length
+        plane.polyline([
+            (-s * r,        c * r, self.height),
+            (c * l - s * r, c * r + s * l, self.height)],
+                       forConstruction=True).tag("dir_top")
+        return result
diff --git a/nhf/parts/test.py b/nhf/parts/test.py
index 7ba7311..b711efa 100644
--- a/nhf/parts/test.py
+++ b/nhf/parts/test.py
@@ -20,8 +20,6 @@ class TestJoints(unittest.TestCase):
                 isect = binary_intersection(assembly)
                 self.assertLess(isect.Volume(), 1e-6,
                                 "Hirth joint assembly must not have intersection")
-    def test_joints_comma_assembly(self):
-        joints.comma_assembly()
 
     def torsion_joint_case(self, joint: joints.TorsionJoint, slot: int):
         assert 0 <= slot and slot < joint.rider_n_slots
diff --git a/nhf/touhou/houjuu_nue/joints.py b/nhf/touhou/houjuu_nue/joints.py
index 05acc97..5d2b895 100644
--- a/nhf/touhou/houjuu_nue/joints.py
+++ b/nhf/touhou/houjuu_nue/joints.py
@@ -1,9 +1,10 @@
+import math
 from dataclasses import dataclass, field
 from typing import Optional, Tuple
 import cadquery as Cq
 from nhf import Material, Role
 from nhf.build import Model, target, assembly
-import nhf.parts.springs as springs
+from nhf.parts.springs import TorsionSpring
 from nhf.parts.joints import TorsionJoint
 from nhf.parts.box import box_with_centre_holes
 import nhf.utils
@@ -23,10 +24,12 @@ class ShoulderJoint(Model):
         rider_disk_height=5.0,
         # M8 Axle
         radius_axle=3.0,
-        # inner diameter = 9
-        radius_spring=9/2 + 1.2,
-        spring_thickness=1.3,
-        spring_height=7.5,
+        spring=TorsionSpring(
+            # inner diameter = 9
+            radius=9/2 + 1.2,
+            thickness=1.3,
+            height=7.5,
+        ),
     ))
 
     # On the parent side, drill vertical holes
@@ -189,12 +192,12 @@ class ShoulderJoint(Model):
             .addS(self.child(), name="child",
                   role=Role.CHILD, material=mat)
             .constrain("child/core", "Fixed")
-            .addS(self.torsion_joint.spring(), name="spring_top",
+            .addS(self.torsion_joint.spring.generate(), name="spring_top",
                   role=Role.DAMPING, material=mat_spring)
             .addS(self.parent(wing_root_wall_thickness),
                   name="parent_top",
                   role=Role.PARENT, material=mat)
-            .addS(self.torsion_joint.spring(), name="spring_bot",
+            .addS(self.torsion_joint.spring.generate(), name="spring_bot",
                   role=Role.DAMPING, material=mat_spring)
             .addS(self.parent(wing_root_wall_thickness),
                   name="parent_bot",
@@ -280,25 +283,27 @@ class DiskJoint(Model):
     """
     Sandwiched disk joint for the wrist and elbow
     """
+    spring: TorsionSpring = field(default_factory=lambda: TorsionSpring(
+        radius=9 / 2,
+        thickness=1.3,
+        height=6.5,
+        tail_length=45.0,
+        right_handed=False,
+    ))
 
     radius_housing: float = 22.0
     radius_disk: float = 20.0
-    radius_spring: float = 9 / 2
     radius_axle: float = 3.0
 
     housing_thickness: float = 5.0
     disk_thickness: float = 5.0
     # Gap between disk and the housing
     #disk_thickness_gap: float = 0.1
-    spring_thickness: float = 1.3
-    spring_height: float = 6.5
-    spring_tail_length: float = 45.0
 
     # 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
+    spring_angle_at_0: float = 30.0
+    spring_slot_offset: float = 15.0
+
     wall_inset: float = 2.0
 
     # Angular span of movement
@@ -317,18 +322,9 @@ class DiskJoint(Model):
         assert self.radius_disk > self.radius_axle
         assert self.housing_upper_carve_offset > 0
 
-    def spring(self):
-        return springs.torsion_spring(
-            radius=self.radius_spring,
-            height=self.spring_height,
-            thickness=self.spring_thickness,
-            tail_length=self.spring_tail_length,
-            right_handed=False,
-        )
-
     @property
     def neutral_movement_angle(self) -> Optional[float]:
-        a = self.spring_angle_neutral - self.spring_angle
+        a = self.spring.angle_neutral - self.spring_angle_at_0
         if 0 <= a and a <= self.movement_angle:
             return a
         return None
@@ -346,7 +342,7 @@ class DiskJoint(Model):
         """
         Distance between the spring track and the outside of the upper housing
         """
-        return self.housing_thickness + self.disk_thickness - self.spring_height
+        return self.housing_thickness + self.disk_thickness - self.spring.height
 
     @property
     def housing_upper_dz(self) -> float:
@@ -355,42 +351,17 @@ class DiskJoint(Model):
         """
         return self.total_thickness / 2 - self.housing_thickness
 
-    @property
-    def radius_spring_internal(self):
-        return self.radius_spring - self.spring_thickness
-
     @target(name="disk")
     def disk(self) -> Cq.Workplane:
         cut = (
             Cq.Solid.makeBox(
-                length=self.spring_tail_length,
-                width=self.spring_thickness,
+                length=self.spring.tail_length,
+                width=self.spring.thickness,
                 height=self.disk_thickness,
             )
-            .located(Cq.Location((0, self.radius_spring_internal, 0)))
-            .rotate((0, 0, 0), (0, 0, 1), self.spring_angle_shift)
+            .located(Cq.Location((0, self.spring.radius_inner, 0)))
+            .rotate((0, 0, 0), (0, 0, 1), self.spring_slot_offset)
         )
-        result = (
-            Cq.Workplane('XY')
-            .cylinder(
-                height=self.disk_thickness,
-                radius=self.radius_disk,
-                centered=(True, True, False)
-            )
-            .copyWorkplane(Cq.Workplane('XY'))
-            .cylinder(
-                height=self.disk_thickness,
-                radius=self.radius_spring,
-                centered=(True, True, False),
-                combine='cut',
-            )
-            .cut(cut)
-        )
-        plane = result.copyWorkplane(Cq.Workplane('XY'))
-        plane.tagPlane("dir", direction="+X")
-        plane.workplane(offset=self.disk_thickness).tagPlane("mate_top")
-        result.copyWorkplane(Cq.Workplane('YX')).tagPlane("mate_bot")
-
         radius_tongue = self.radius_disk + self.tongue_length
         tongue = (
             Cq.Solid.makeCylinder(
@@ -402,7 +373,29 @@ class DiskJoint(Model):
                 radius=self.radius_disk,
             ))
         )
-        result = result.union(tongue, tol=TOL)
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                height=self.disk_thickness,
+                radius=self.radius_disk,
+                centered=(True, True, False)
+            )
+            .union(tongue, tol=TOL)
+            .copyWorkplane(Cq.Workplane('XY'))
+            .cylinder(
+                height=self.disk_thickness,
+                radius=self.spring.radius,
+                centered=(True, True, False),
+                combine='cut',
+            )
+            .cut(cut)
+        )
+        plane = result.copyWorkplane(Cq.Workplane('XY'))
+        theta = math.radians(self.spring_slot_offset)
+        plane.tagPlane("dir", direction=(math.cos(theta), math.sin(theta), 0))
+        plane.workplane(offset=self.disk_thickness).tagPlane("mate_top")
+        result.copyWorkplane(Cq.Workplane('YX')).tagPlane("mate_bot")
+
         return result
 
     def wall(self) -> Cq.Compound:
@@ -433,9 +426,6 @@ class DiskJoint(Model):
         )
         result.faces(">Z").tag("mate")
         result.faces(">Z").workplane().tagPlane("dirX", direction="+X")
-        # two directional vectors are required to make the angle constrain
-        # unambiguous
-        result.faces(">Z").workplane().tagPlane("dirY", direction="+Y")
         result = result.cut(
             self
             .wall()
@@ -447,16 +437,17 @@ class DiskJoint(Model):
 
     @target(name="housing-upper")
     def housing_upper(self) -> Cq.Workplane:
+        carve_angle = -(self.spring_angle_at_0 - self.spring_slot_offset)
         carve = (
             Cq.Solid.makeCylinder(
-                radius=self.radius_spring,
+                radius=self.spring.radius,
                 height=self.housing_thickness
             ).fuse(Cq.Solid.makeBox(
-                length=self.spring_tail_length,
-                width=self.spring_thickness,
+                length=self.spring.tail_length,
+                width=self.spring.thickness,
                 height=self.housing_thickness
-            ).located(Cq.Location((0, -self.radius_spring, 0))))
-        ).rotate((0, 0, 0), (0, 0, 1), self.spring_angle - self.spring_angle_shift)
+            ).located(Cq.Location((0, -self.spring.radius, 0))))
+        ).rotate((0, 0, 0), (0, 0, 1), carve_angle)
         result = (
             Cq.Workplane('XY')
             .cylinder(
@@ -465,8 +456,11 @@ class DiskJoint(Model):
                 centered=(True, True, False),
             )
         )
+        theta = math.radians(carve_angle)
         result.faces("<Z").tag("mate")
-        result.copyWorkplane(Cq.Workplane('XY')).tagPlane("dir", direction="+X")
+        p_xy = result.copyWorkplane(Cq.Workplane('XY'))
+        p_xy.tagPlane("dirX", direction="+X")
+        p_xy.tagPlane("dir", direction=(math.cos(theta), math.sin(theta), 0))
         result = result.faces(">Z").hole(self.radius_axle * 2)
 
         # tube which holds the spring interior
@@ -490,28 +484,42 @@ class DiskJoint(Model):
             .cut(carve.located(Cq.Location((0, 0, -self.housing_upper_carve_offset))))
             .union(wall, tol=TOL)
         )
-        return result
+        return result.clean()
 
     def add_constraints(self,
                         assembly: Cq.Assembly,
                         housing_lower: str,
                         housing_upper: str,
                         disk: str,
-                        angle: float,
+                        angle: float = 0.0,
                         ) -> Cq.Assembly:
-        return (
+        deflection = angle - self.neutral_movement_angle
+        spring_name = disk.replace("/", "__Z") + "_spring"
+        (
             assembly
+            .addS(
+                self.spring.generate(deflection=-deflection),
+                name=spring_name,
+                role=Role.DAMPING,
+                material=Material.STEEL_SPRING)
             .constrain(f"{disk}?mate_bot", f"{housing_lower}?mate", "Plane")
             .constrain(f"{disk}?mate_top", f"{housing_upper}?mate", "Plane")
-            .constrain(f"{housing_lower}?dirX", f"{housing_upper}?dir", "Axis", param=0)
-            .constrain(f"{housing_lower}?dirX", f"{disk}?dir", "Axis", param=angle)
-            .constrain(f"{housing_lower}?dirY", f"{disk}?dir", "Axis", param=angle - 90)
+            .constrain(f"{housing_lower}?dirX", f"{housing_upper}?dirX", "Axis", param=0)
+            .constrain(f"{housing_upper}?dir", f"{spring_name}?dir_top", "Axis", param=0)
+            .constrain(f"{spring_name}?dir_bot", f"{disk}?dir", "Axis", param=0)
+            .constrain(f"{disk}?mate_bot", f"{spring_name}?bot", "Plane", param=0)
+            #.constrain(f"{housing_lower}?dirX", f"{housing_upper}?dir", "Axis", param=0)
+            #.constrain(f"{housing_lower}?dirX", f"{disk}?dir", "Axis", param=angle)
+            #.constrain(f"{housing_lower}?dirY", f"{disk}?dir", "Axis", param=angle - 90)
+        )
+        return (
+            assembly
         )
 
 
     def assembly(self, angle: Optional[float] = 0) -> Cq.Assembly:
         if angle is None:
-            angle = self.movement_angle
+            angle = self.neutral_movement_angle
             if angle is None:
                 angle = 0
         else:
@@ -521,7 +529,7 @@ class DiskJoint(Model):
             .addS(self.disk(), name="disk", role=Role.CHILD)
             .addS(self.housing_lower(), name="housing_lower", role=Role.PARENT)
             .addS(self.housing_upper(), name="housing_upper", role=Role.CASING)
-            #.constrain("housing_lower", "Fixed")
+            .constrain("housing_lower", "Fixed")
         )
         result = self.add_constraints(
             result,
@@ -627,10 +635,15 @@ class ElbowJoint:
             .rotate((0,0,0), (0,0,1), 180-self.parent_arm_span / 2)
         )
         housing = self.disk_joint.housing_upper()
+        housing_loc = Cq.Location(
+            (0, 0, housing_dz),
+            (0, 0, 1),
+            -self.disk_joint.tongue_span / 2
+        )
         result = (
             self.parent_beam.beam()
             .add(housing, name="housing",
-                 loc=axial_offset * Cq.Location((0, 0, housing_dz)))
+                 loc=axial_offset * housing_loc)
             .add(connector, name="connector",
                  loc=axial_offset)
             #.constrain("housing", "Fixed")
diff --git a/nhf/touhou/houjuu_nue/wing.py b/nhf/touhou/houjuu_nue/wing.py
index b520384..99fcde2 100644
--- a/nhf/touhou/houjuu_nue/wing.py
+++ b/nhf/touhou/houjuu_nue/wing.py
@@ -545,7 +545,8 @@ class WingProfile(Model):
         return result.solve()
 
     def assembly(self,
-                 parts: Optional[list[str]] = None
+                 parts: Optional[list[str]] = None,
+                 angle_elbow_wrist: float = 0.0,
                  ) -> Cq.Assembly():
         if parts is None:
             parts = ["s0", "shoulder", "s1", "elbow", "s2", "wrist", "s3"]
@@ -575,7 +576,7 @@ class WingProfile(Model):
                 .constrain("s1/shoulder_bot?conn1", "shoulder/child/lip_bot?conn1", "Plane")
             )
         if "elbow" in parts:
-            result.add(self.elbow_joint.assembly(), name="elbow")
+            result.add(self.elbow_joint.assembly(angle=angle_elbow_wrist), name="elbow")
         if "s1" in parts and "elbow" in parts:
             (
                 result
@@ -595,24 +596,25 @@ class WingProfile(Model):
                 .constrain("s2/elbow_bot?conn1", "elbow/child/bot?conn1", "Plane")
             )
         if "wrist" in parts:
-            result.add(self.wrist_joint.assembly(), name="wrist")
+            result.add(self.wrist_joint.assembly(angle=angle_elbow_wrist), name="wrist")
         if "s2" in parts and "wrist" in parts:
+            # Mounted backwards to bend in other direction
             (
                 result
-                .constrain("s2/wrist_top?conn0", "wrist/parent_upper/top?conn0", "Plane")
-                .constrain("s2/wrist_top?conn1", "wrist/parent_upper/top?conn1", "Plane")
-                .constrain("s2/wrist_bot?conn0", "wrist/parent_upper/bot?conn0", "Plane")
-                .constrain("s2/wrist_bot?conn1", "wrist/parent_upper/bot?conn1", "Plane")
+                .constrain("s2/wrist_top?conn0", "wrist/parent_upper/bot?conn0", "Plane")
+                .constrain("s2/wrist_top?conn1", "wrist/parent_upper/bot?conn1", "Plane")
+                .constrain("s2/wrist_bot?conn0", "wrist/parent_upper/top?conn0", "Plane")
+                .constrain("s2/wrist_bot?conn1", "wrist/parent_upper/top?conn1", "Plane")
             )
         if "s3" in parts:
             result.add(self.assembly_s3(), name="s3")
         if "s3" in parts and "wrist" in parts:
             (
                 result
-                .constrain("s3/wrist_top?conn0", "wrist/child/top?conn0", "Plane")
-                .constrain("s3/wrist_top?conn1", "wrist/child/top?conn1", "Plane")
-                .constrain("s3/wrist_bot?conn0", "wrist/child/bot?conn0", "Plane")
-                .constrain("s3/wrist_bot?conn1", "wrist/child/bot?conn1", "Plane")
+                .constrain("s3/wrist_top?conn0", "wrist/child/bot?conn0", "Plane")
+                .constrain("s3/wrist_top?conn1", "wrist/child/bot?conn1", "Plane")
+                .constrain("s3/wrist_bot?conn0", "wrist/child/top?conn0", "Plane")
+                .constrain("s3/wrist_bot?conn1", "wrist/child/top?conn1", "Plane")
             )
         if len(parts) > 1:
             result.solve()