nhf/build.py

@@ -0,0 +1,307 @@
+"""
+The NHF build system
+
+Usage: For any parametric assembly, inherit the `Model` class, and mark the
+output objects with the `@target` decorator. Each marked function should only
+take `self` as an argument.
+```python
+class BuildScaffold(Model):
+
+    @target(name="obj1")
+    def o1(self):
+        return Cq.Solid.makeBox(10, 10, 10)
+
+    def o2(self):
+        return Cq.Solid.makeCylinder(10, 20)
+```
+"""
+from enum import Enum
+from pathlib import Path
+from typing import Union, Optional
+from functools import wraps
+import traceback
+from colorama import Fore, Style
+import cadquery as Cq
+import nhf.checks as NC
+import nhf.utils
+
+TOL=1e-6
+
+class TargetKind(Enum):
+
+    STL = "stl",
+    DXF = "dxf",
+
+    def __init__(self, ext: str):
+        self.ext = ext
+
+class Target:
+    """
+    Marks a function's output for serialization
+    """
+
+    def __init__(self,
+                 method,
+                 name: Optional[str] = None,
+                 prototype: bool = False,
+                 kind: TargetKind = TargetKind.STL,
+                 **kwargs):
+        self._method = method
+        self.name = name
+        self.prototype = prototype
+        self.kind = kind
+        self.kwargs = kwargs
+    def __str__(self):
+        return f"<target {self.name}.{self.kind.ext} {self._method}>"
+    def __call__(self, obj, *args, **kwargs):
+        """
+        Raw call function which passes arguments directly to `_method`
+        """
+        return self._method(obj, *args, **kwargs)
+
+    @property
+    def file_name(self) -> Optional[str]:
+        """
+        Output file name
+        """
+        if self.name:
+            return f"{self.name}.{self.kind.ext}"
+        else:
+            return None
+
+    def write_to(self, obj, path: str) -> bool:
+        """
+        Returns false if target is `None`
+        """
+        x = self._method(obj)
+        if x is None:
+            return False
+        if self.kind == TargetKind.STL:
+            assert isinstance(x, Union[
+                Cq.Workplane, Cq.Shape, Cq.Compound, Cq.Assembly])
+            if isinstance(x, Cq.Workplane):
+                x = x.val()
+            if isinstance(x, Cq.Assembly):
+                x = x.toCompound().fuse(tol=TOL)
+            x.exportStl(path, **self.kwargs)
+        elif self.kind == TargetKind.DXF:
+            if isinstance(x, Cq.Sketch):
+                # https://github.com/CadQuery/cadquery/issues/1575
+                x = (
+                    Cq.Workplane()
+                    .add(x._faces)
+                    .add(x._wires)
+                    .add(x._edges)
+                )
+            assert isinstance(x, Cq.Workplane)
+            Cq.exporters.exportDXF(x, path, **self.kwargs)
+        else:
+            assert False, f"Invalid kind: {self.kind}"
+        return True
+
+    @classmethod
+    def methods(cls, subject):
+        """
+        List of all methods of a class or objects annotated with this decorator.
+        """
+        def g():
+            for name in dir(subject):
+                if name == 'target_names':
+                    continue
+                method = getattr(subject, name)
+                if hasattr(method, '_target'):
+                    yield method._target
+        return {method.name: method for method in g()}
+
+
+def target(**deco_kwargs):
+    """
+    Decorator for annotating a build output
+    """
+    def f(method):
+        @wraps(method)
+        def wrapper(self, *args, **kwargs):
+            return method(self, *args, **kwargs)
+        wrapper._target = Target(method, **deco_kwargs)
+        return wrapper
+    return f
+
+class Assembly:
+    """
+    Marks a function's output for assembly property checking
+    """
+
+    def __init__(self,
+                 method,
+                 collision_check: bool = True,
+                 **kwargs):
+        self._method = method
+        self.name = method.__name__
+        self.collision_check = collision_check
+        self.kwargs = kwargs
+    def __str__(self):
+        return f"<assembly {self.name} {self._method}>"
+    def __call__(self, obj, *args, **kwargs):
+        """
+        Raw call function which passes arguments directly to `_method`
+        """
+        return self._method(obj, *args, **kwargs)
+
+    def check(self, obj):
+        x = self._method(obj)
+        assert isinstance(x, Cq.Assembly)
+        if self.collision_check:
+            intersections = NC.pairwise_intersection(x)
+            assert not intersections, f"In {self}, collision detected: {intersections}"
+
+    @classmethod
+    def methods(cls, subject):
+        """
+        List of all methods of a class or objects annotated with this decorator.
+        """
+        def g():
+            for name in dir(subject):
+                if name == 'target_names':
+                    continue
+                method = getattr(subject, name)
+                if hasattr(method, '_assembly'):
+                    yield method._assembly
+        return {method.name: method for method in g()}
+
+def assembly(**deco_kwargs):
+    """
+    Decorator for annotating an assembly output
+    """
+    def f(method):
+        @wraps(method)
+        def wrapper(self, *args, **kwargs):
+            return method(self, *args, **kwargs)
+        wrapper._assembly = Assembly(method, **deco_kwargs)
+        return wrapper
+    return f
+
+
+
+class Submodel:
+    """
+    Marks a function's output as a submodel
+    """
+
+    def __init__(self,
+                 method,
+                 name: str,
+                 prototype: bool = False,
+                 **kwargs):
+        self._method = method
+        self.name = name
+        self.prototype = prototype
+        self.kwargs = kwargs
+    def __str__(self):
+        return f"<submodel {self.name} {self._method}>"
+    def __call__(self, obj, *args, **kwargs):
+        """
+        Raw call function which passes arguments directly to `_method`
+        """
+        return self._method(obj, *args, **kwargs)
+
+    @property
+    def file_name(self):
+        """
+        Output file name
+        """
+        return self.name
+
+    def write_to(self, obj, path: str):
+        x = self._method(obj)
+        assert isinstance(x, Model), f"Unexpected type: {type(x)}"
+        x.build_all(path)
+
+    @classmethod
+    def methods(cls, subject):
+        """
+        List of all methods of a class or objects annotated with this decorator.
+        """
+        def g():
+            for name in dir(subject):
+                if name == 'target_names':
+                    continue
+                method = getattr(subject, name)
+                if hasattr(method, '_submodel'):
+                    yield method._submodel
+        return {method.name: method for method in g()}
+
+
+def submodel(name, **deco_kwargs):
+    """
+    Decorator for annotating a build output
+    """
+    def f(method):
+        @wraps(method)
+        def wrapper(self, *args, **kwargs):
+            return method(self, *args, **kwargs)
+        wrapper._submodel = Submodel(method, name, **deco_kwargs)
+        return wrapper
+    return f
+
+class Model:
+    """
+    Base class for a parametric assembly
+    """
+    def __init__(self, name: Optional[str] = None):
+        self.name = name
+
+    @property
+    def target_names(self) -> list[str]:
+        """
+        List of decorated target functions
+        """
+        return list(Target.methods(self).keys())
+
+    def check_all(self) -> int:
+        """
+        Build all models and run all the checks. Return number of checks passed
+        """
+        total = 0
+        for t in Target.methods(self).values():
+            result = t(self)
+            if result:
+                total += 1
+        for t in Assembly.methods(self).values():
+            t.check(self)
+            total += 1
+        return total
+
+    def build_all(self, output_dir: Union[Path, str] = "build", verbose=1):
+        """
+        Build all targets in this model and write the results to file
+        """
+        output_dir = Path(output_dir)
+        targets = Target.methods(self)
+        for t in targets.values():
+            file_name = t.file_name
+            if file_name is None:
+                assert len(targets) == 1, "Only one anonymous target is permitted"
+                output_file = output_dir.with_suffix('.' + t.kind.ext)
+            else:
+                output_file = output_dir / file_name
+
+            if output_file.is_file():
+                if verbose >= 1:
+                    print(f"{Fore.GREEN}Skipping{Style.RESET_ALL} {output_file}")
+                continue
+            output_file.parent.mkdir(exist_ok=True, parents=True)
+
+            if verbose >= 1:
+                print(f"{Fore.BLUE}Building{Style.RESET_ALL} {output_file}")
+
+            try:
+                flag = t.write_to(self, str(output_file))
+                if flag and verbose >= 1:
+                    print(f"{Fore.GREEN}Built{Style.RESET_ALL} {output_file}")
+            except Exception as e:
+                print(f"{Fore.RED}Failed to build{Style.RESET_ALL} {output_file}: {e}")
+                traceback.print_exc()
+
+        for t in Submodel.methods(self).values():
+            d = output_dir / t.name
+            t.write_to(self, str(d))

nhf/checks.py

@@ -0,0 +1,64 @@
+import cadquery as Cq
+
+def binary_intersection(a: Cq.Assembly) -> Cq.Shape:
+    objs = [s.toCompound() for _, s in a.traverse()
+            if isinstance(s, Cq.Assembly)]
+    obj1, obj2 = objs[:2]
+    return obj1.intersect(obj2)
+
+def visualize_intersection(assembly: Cq.Assembly, tol: float=1e-6) -> Cq.Shape:
+    """
+    Given an assembly, test the pairwise intersection volume of its components.
+    Return the pairs whose intersection volume exceeds `tol`.
+    """
+    m = {name: (i, shape.moved(loc))
+         for i, (shape, name, loc, _)
+         in enumerate(assembly)}
+    for name, (i1, sh1) in m.items():
+        for name2, (i2, sh2) in m.items():
+            if name == name2:
+                assert i1 == i2
+                continue
+            if i2 <= i1:
+                # Remove the upper diagonal
+                continue
+            head = name.split('/', 2)[1]
+            head2 = name2.split('/', 2)[1]
+            if head == head2:
+                # Do not test into subassemblies
+                continue
+
+            isect = sh1.intersect(sh2)
+            vol = isect.Volume()
+            if vol > tol:
+                return isect
+    return None
+
+def pairwise_intersection(assembly: Cq.Assembly, tol: float=1e-6) -> list[(str, str, float)]:
+    """
+    Given an assembly, test the pairwise intersection volume of its components.
+    Return the pairs whose intersection volume exceeds `tol`.
+    """
+    m = {name: (i, shape.moved(loc))
+         for i, (shape, name, loc, _)
+         in enumerate(assembly)}
+    result = []
+    for name, (i1, sh1) in m.items():
+        for name2, (i2, sh2) in m.items():
+            if name == name2:
+                assert i1 == i2
+                continue
+            if i2 <= i1:
+                # Remove the upper diagonal
+                continue
+            head = name.split('/', 2)[1]
+            head2 = name2.split('/', 2)[1]
+            if head == head2:
+                # Do not test into subassemblies
+                continue
+
+
+            vol = sh1.intersect(sh2).Volume()
+            if vol > tol:
+                result.append((name, name2, vol))
+    return result

nhf/diag.py

@@ -0,0 +1,42 @@
+import cadquery as Cq
+
+def tidy_repr(obj):
+    """Shortens a default repr string"""
+    return repr(obj).split(".")[-1].rstrip(">")
+
+
+def _ctx_str(self):
+    return (
+        tidy_repr(self)
+        + ":\n"
+        + f"    pendingWires: {self.pendingWires}\n"
+        + f"    pendingEdges: {self.pendingEdges}\n"
+        + f"    tags: {self.tags}"
+    )
+
+
+Cq.cq.CQContext.__str__ = _ctx_str
+
+
+def _plane_str(self):
+    return (
+        tidy_repr(self)
+        + ":\n"
+        + f"    origin: {self.origin.toTuple()}\n"
+        + f"    z direction: {self.zDir.toTuple()}"
+    )
+
+
+Cq.occ_impl.geom.Plane.__str__ = _plane_str
+
+
+def _wp_str(self):
+    out = tidy_repr(self) + ":\n"
+    out += f"  parent: {tidy_repr(self.parent)}\n" if self.parent else "  no parent\n"
+    out += f"  plane: {self.plane}\n"
+    out += f"  objects: {self.objects}\n"
+    out += f"  modelling context: {self.ctx}"
+    return out
+
+
+Cq.Workplane.__str__ = _wp_str

nhf/geometry.py

@@ -0,0 +1,110 @@
+"""
+Geometry functions
+"""
+from typing import Tuple, Optional
+import math
+
+def min_radius_contraction_span_pos(
+        d_open: float,
+        d_closed: float,
+        theta: float,
+    ) -> Tuple[float, float]:
+    """
+    Calculates the position of the two ends of an actuator, whose fully opened
+    length is `d_open`, closed length is `d_closed`, and whose motion spans a
+    range `theta` (in radians). Returns (r, phi): If one end of the actuator is
+    held at `(r, 0)`, then the other end will trace an arc `r` away from the
+    origin with span `theta`
+
+    Let `P` (resp. `P'`) be the position of the front of the actuator when its
+    fully open (resp. closed), `Q` be the position of the back of the actuator,
+    we note that `OP = OP' = OQ`.
+    """
+    assert d_open > d_closed
+    assert 0 < theta < math.pi
+
+    pq2 = d_open * d_open
+    p_q2 = d_closed * d_closed
+    # angle of PQP'
+    psi = 0.5 * theta
+    # |P-P'|, via the triangle PQP'
+    pp_2 = pq2 + p_q2 - 2 * d_open * d_closed * math.cos(psi)
+    r2 = pp_2 / (2 - 2 * math.cos(theta))
+    # Law of cosines on POQ:
+    phi = math.acos(1 - pq2 / 2 / r2)
+    return math.sqrt(r2), phi
+
+def min_tangent_contraction_span_pos(
+        d_open: float,
+        d_closed: float,
+        theta: float,
+    ) -> Tuple[float, float, float]:
+    """
+    Returns `(r, phi, r')` where `r` is the distance of the arm to origin, `r'`
+    is the distance of the base to origin, and `phi` the angle in the open
+    state.
+    """
+    assert d_open > d_closed
+    assert 0 < theta < math.pi
+    # Angle of OPQ = OPP'
+    pp_ = d_open - d_closed
+    pq = d_open
+    p_q = d_closed
+
+    a = (math.pi - theta) / 2
+    # Law of sines on POP'
+    r = math.sin(a) / math.sin(theta) * pp_
+    # Law of cosine on OPQ
+    oq = math.sqrt(r * r + pq * pq - 2 * r * pq * math.cos(a))
+    # Law of sines on OP'Q. Not using OPQ for numerical reasons since the angle
+    # `phi` could be very close to `pi/2`
+    phi_ = math.asin(math.sin(a) / oq * p_q)
+    phi = phi_ + theta
+    assert theta <= phi < math.pi
+    return r, phi, oq
+
+def contraction_span_pos_from_radius(
+        d_open: float,
+        d_closed: float,
+        theta: float,
+        r: Optional[float] = None,
+        smaller: bool = True,
+    ) -> Tuple[float, float, float]:
+    """
+    Returns `(r, phi, r')`
+
+    Set `smaller` to false to use the other solution, which has a larger
+    profile.
+    """
+    if r is None:
+        return min_tangent_contraction_span_pos(
+            d_open=d_open,
+            d_closed=d_closed,
+            theta=theta)
+    assert 0 < theta < math.pi
+    assert d_open > d_closed
+    assert r > 0
+    # Law of cosines
+    pp_ = r * math.sqrt(2 * (1 - math.cos(theta)))
+    d = d_open - d_closed
+    assert pp_ > d, f"Triangle inequality is violated. This joint is impossible: {pp_}, {d}"
+    assert d_open + d_closed > pp_, f"The span is too great to cover with this stroke length: {pp_}"
+    # Angle of PP'Q, via a numerically stable acos
+    beta = math.acos(
+        - d / pp_ * (1 + d / (2 * d_closed))
+        + pp_ / (2 * d_closed))
+    # Two solutions based on angle complementarity
+    if smaller:
+        contra_phi = beta - (math.pi - theta) / 2
+    else:
+        # technically there's a 2pi in front
+        contra_phi = -(math.pi - theta) / 2 - beta
+    # Law of cosines, calculates `r'`
+    r_ = math.sqrt(
+        r * r + d_closed * d_closed - 2 * r * d_closed * math.cos(contra_phi)
+    )
+    # sin phi_ / P'Q = sin contra_phi / r'
+    phi_ = math.asin(math.sin(contra_phi) / r_ * d_closed)
+    assert phi_ > 0, f"Actuator would need to traverse pass its minimal point, {math.degrees(phi_)}"
+    assert 0 <= theta + phi_ <= math.pi
+    return r, theta + phi_, r_

nhf/parts/box.py

@@ -0,0 +1,157 @@
+import cadquery as Cq
+from dataclasses import dataclass, field
+from typing import Tuple, Optional, Union, Callable
+from nhf.build import Model, TargetKind, target
+import nhf.utils
+
+def box_with_centre_holes(
+        length: float,
+        width: float,
+        height: float,
+        hole_loc: list[float],
+        hole_diam: float = 6.0,
+        ) -> Cq.Workplane:
+    """
+    Creates a box with holes along the X axis, marked `conn0, conn1, ...`. The
+    box's y axis is centred
+    """
+    result = (
+        Cq.Workplane('XY')
+        .box(length, width, height, centered=(False, True, False))
+        .faces(">Z")
+        .workplane()
+    )
+    plane = result
+    for i, x in enumerate(hole_loc):
+        result = result.moveTo(x, 0).hole(hole_diam)
+        plane.moveTo(x, 0).tagPlane(f"conn{i}")
+    return result
+
+@dataclass
+class Hole:
+    x: float
+    y: float = 0.0
+    diam: Optional[float] = None
+    tag: Optional[str] = None
+    face: Optional[Cq.Face] = None
+
+    @property
+    def rev_tag(self) -> str:
+        assert self.tag is not None
+        return self.tag + "_rev"
+
+    def cutting_geometry(self, default_diam: Optional[float] = None) -> Cq.Face:
+        if self.face is not None:
+            return self.face
+        diam = self.diam if self.diam is not None else default_diam
+        assert diam is not None
+        return Cq.Face.makeFromWires(Cq.Wire.makeCircle(diam/2, Cq.Vector(), Cq.Vector(0,0,1)))
+
+@dataclass
+class MountingBox(Model):
+    """
+    Create a box with marked holes
+    """
+    length: float = 100.0
+    width: float = 60.0
+    thickness: float = 1.0
+
+    # List of (x, y), diam
+    holes: list[Hole] = field(default_factory=lambda: [])
+    hole_diam: Optional[float] = None
+
+    centred: Tuple[bool, bool] = (False, True)
+
+    generate_side_tags: bool = True
+    # Generate tags on the opposite side
+    generate_reverse_tags: bool = False
+
+    centre_bot_top_tags: bool = False
+    centre_left_right_tags: bool = False
+
+    # Determines the position of side tags
+    flip_y: bool = False
+
+    profile_callback: Optional[Callable[[Cq.Sketch], Cq.Sketch]] = None
+
+    def __post_init__(self):
+        assert self.thickness > 0
+        for i, hole in enumerate(self.holes):
+            if hole.tag is None:
+                hole.tag = f"conn{i}"
+
+    @target(kind=TargetKind.DXF)
+    def profile(self) -> Cq.Sketch:
+        bx, by = 0, 0
+        if not self.centred[0]:
+            bx = self.length / 2
+        if not self.centred[1]:
+            by = self.width / 2
+        result = (
+            Cq.Sketch()
+            .push([(bx, by)])
+            .rect(self.length, self.width)
+        )
+        for hole in self.holes:
+            face = hole.cutting_geometry(default_diam=self.hole_diam)
+            result.push([(hole.x, hole.y)]).each(lambda l:face.moved(l), mode='s')
+        if self.profile_callback:
+            result = self.profile_callback(result)
+        return result
+
+    def generate(self) -> Cq.Workplane:
+        """
+        Creates box shape with markers
+        """
+        result = (
+            Cq.Workplane('XY')
+            .placeSketch(self.profile())
+            .extrude(self.thickness)
+        )
+        plane = result.copyWorkplane(Cq.Workplane('XY')).workplane(offset=self.thickness)
+        reverse_plane = result.copyWorkplane(Cq.Workplane('XY'))
+        for hole in self.holes:
+            assert hole.tag
+            plane.moveTo(hole.x, hole.y).tagPlane(hole.tag)
+            if self.generate_reverse_tags:
+                reverse_plane.moveTo(hole.x, hole.y).tagPlane(hole.rev_tag, '-Z')
+
+        if self.generate_side_tags:
+            xn, xp = 0, self.length
+            if self.centred[0]:
+                xn -= self.length/2
+                xp -= self.length/2
+            yn, yp = 0, self.width
+            if self.centred[1]:
+                yn -= self.width/2
+                yp -= self.width/2
+
+            tag_x = xn + (self.length/2 if self.centre_left_right_tags else 0)
+            result.copyWorkplane(Cq.Workplane('XZ', origin=(tag_x, yn, self.thickness))).tagPlane("left")
+            result.copyWorkplane(Cq.Workplane('ZX', origin=(tag_x, yp, self.thickness))).tagPlane("right")
+
+            tag_y = yn + (self.width/2 if self.centre_bot_top_tags else 0)
+            result.copyWorkplane(Cq.Workplane('ZY', origin=(xn, tag_y, self.thickness))).tagPlane("bot")
+            result.copyWorkplane(Cq.Workplane('YZ', origin=(xp, tag_y, self.thickness))).tagPlane("top")
+            result.faces(">Z").tag("dir")
+        return result
+
+    def marked_assembly(self) -> Cq.Assembly:
+        result = (
+            Cq.Assembly()
+            .add(self.generate(), name="box")
+        )
+        for hole in self.holes:
+            result.markPlane(f"box?{hole.tag}")
+            if self.generate_reverse_tags:
+                result.markPlane(f"box?{hole.rev_tag}")
+        if self.generate_side_tags:
+            (
+                result
+                .markPlane("box?left")
+                .markPlane("box?right")
+                .markPlane("box?dir")
+                .markPlane("box?top")
+                .markPlane("box?bot")
+            )
+        return result.solve()

nhf/parts/electronics.py

@@ -0,0 +1,135 @@
+from dataclasses import dataclass, field
+from typing import Tuple
+import cadquery as Cq
+from nhf import Item, Role
+from nhf.parts.box import Hole, MountingBox
+import nhf.utils
+
+@dataclass(frozen=True)
+class ArduinoUnoR3(Item):
+    # From datasheet
+    mass: float = 25.0
+    length: float = 68.6
+    width: float = 53.4
+
+    # with clearance
+    base_height: float = 5.0
+    # aesthetic only for illustrating clearance
+    total_height: float = 50.0
+    roof_height: float = 20.0
+
+    # This is labeled in mirrored coordinates from top down (i.e. unmirrored from bottom up)
+    holes: list[Tuple[float, float]] = field(default_factory=lambda: [
+        (15.24, 2.54),
+        (15.24 - 1.270, 50.80), # x coordinate not labeled on schematic
+        (66.04, 17.78),
+        (66.04, 45.72),
+    ])
+    hole_diam: float = 3.0
+
+    @property
+    def name(self) -> str:
+        return "Arduino Uno R3"
+
+    @property
+    def role(self) -> Role:
+        return Role.ELECTRONIC
+
+    def generate(self) -> Cq.Assembly:
+        sketch = (
+            Cq.Sketch()
+            .polygon([
+                (0,0),
+                (self.length, 0),
+                (self.length, self.width),
+                (0,self.width)
+            ])
+            .push([(x, self.width - y) for x,y in self.holes])
+            .circle(self.hole_diam / 2, mode='s')
+        )
+        # pillar thickness
+        t = 3.0
+        pillar_height = self.total_height - self.base_height
+        pillar = Cq.Solid.makeBox(
+            t, t, pillar_height
+        )
+        roof = Cq.Solid.makeBox(
+            self.length, self.width, t
+        )
+        result = (
+            Cq.Workplane('XY')
+            .placeSketch(sketch)
+            .extrude(self.base_height)
+            .union(pillar.located(Cq.Location((0, 0, self.base_height))))
+            .union(pillar.located(Cq.Location((self.length - t, 0, self.base_height))))
+            .union(pillar.located(Cq.Location((self.length - t, self.width - t, self.base_height))))
+            .union(pillar.located(Cq.Location((0, self.width - t, self.base_height))))
+            .union(roof.located(Cq.Location((0, 0, self.total_height - t))))
+        )
+        plane = result.copyWorkplane(Cq.Workplane('XY'))
+        for i, (x, y) in enumerate(self.holes):
+            plane.moveTo(x, self.width - y).tagPlane(f"conn{i}", direction='-Z')
+        return result
+
+
+@dataclass(frozen=True)
+class BatteryBox18650(Item):
+    """
+    A number of 18650 batteries in series
+    """
+    mass: float = 17.4 + 68.80 * 3
+    length: float = 75.70
+    width_base: float = 61.46 - 18.48 - 20.18 * 2
+    battery_dist: float = 20.18
+    height: float = 19.66
+    # space from bottom to battery begin
+    thickness: float = 1.66
+    battery_diam: float = 18.48
+    battery_height: float = 68.80
+    n_batteries: int = 3
+
+    def __post_init__(self):
+        assert 2 * self.thickness < min(self.length, self.height)
+
+    @property
+    def name(self) -> str:
+        return f"BatteryBox 18650*{self.n_batteries}"
+
+    @property
+    def role(self) -> Role:
+        return Role.ELECTRONIC
+
+    def generate(self) -> Cq.Workplane:
+        width = self.width_base + self.battery_dist * (self.n_batteries - 1) + self.battery_diam
+        return (
+            Cq.Workplane('XY')
+            .box(
+                length=self.length,
+                width=width,
+                height=self.height,
+                centered=(True, True, False),
+            )
+            .copyWorkplane(Cq.Workplane('XY', origin=(0, 0, self.thickness)))
+            .box(
+                length=self.length - self.thickness*2,
+                width=width - self.thickness*2,
+                height=self.height - self.thickness,
+                centered=(True, True, False),
+                combine='cut',
+            )
+            .copyWorkplane(Cq.Workplane('XY', origin=(-self.battery_height/2, 0, self.thickness + self.battery_diam/2)))
+            .rarray(
+                xSpacing=1,
+                ySpacing=self.battery_dist,
+                xCount=1,
+                yCount=self.n_batteries,
+                center=True,
+            )
+            .cylinder(
+                radius=self.battery_diam/2,
+                height=self.battery_height,
+                direct=(1, 0, 0),
+                centered=(True, True, False),
+                combine=True,
+            )
+        )

nhf/parts/fasteners.py

@@ -0,0 +1,162 @@
+from dataclasses import dataclass
+import math
+import cadquery as Cq
+from typing import Optional
+from nhf import Item, Role
+import nhf.utils
+
+@dataclass(frozen=True)
+class FlatHeadBolt(Item):
+    diam_head: float
+    height_head: float
+    diam_thread: float
+    height_thread: float
+
+    @property
+    def name(self) -> str:
+        return f"Bolt M{int(self.diam_thread)} h{int(self.height_thread)}mm"
+
+    @property
+    def role(self) -> Role:
+        return Role.CONNECTION
+
+
+    def generate(self) -> Cq.Assembly:
+        head = Cq.Solid.makeCylinder(
+            radius=self.diam_head / 2,
+            height=self.height_head,
+        )
+        rod = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.diam_thread/ 2,
+                height=self.height_thread,
+                centered=(True, True, False))
+        )
+        rod.faces("<Z").tag("tip")
+        rod.faces(">Z").tag("root")
+        rod = rod.union(head.located(Cq.Location((0, 0, self.height_thread))))
+        return rod
+
+
+@dataclass(frozen=True)
+class ThreaddedKnob(Item):
+    """
+    A threaded rod with knob on one side
+    """
+    diam_thread: float
+    height_thread: float
+    diam_knob: float
+
+    diam_neck: float
+    height_neck: float
+    height_knob: float
+
+    @property
+    def name(self) -> str:
+        return f"Knob M{int(self.diam_thread)} h{int(self.height_thread)}mm"
+
+    def generate(self) -> Cq.Assembly:
+        knob = Cq.Solid.makeCylinder(
+            radius=self.diam_knob / 2,
+            height=self.height_knob,
+        )
+        neck = Cq.Solid.makeCylinder(
+            radius=self.diam_neck / 2,
+            height=self.height_neck,
+        )
+        thread = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.diam_thread / 2,
+                height=self.height_thread,
+                centered=(True, True, False))
+        )
+        thread.faces("<Z").tag("tip")
+        thread.faces(">Z").tag("root")
+
+        return (
+            Cq.Assembly()
+            .addS(thread, name="thread", role=Role.CONNECTION)
+            .addS(neck, name="neck", role=Role.HANDLE,
+                  loc=Cq.Location((0, 0, self.height_thread)))
+            .addS(knob, name="knob", role=Role.HANDLE,
+                  loc=Cq.Location((0, 0, self.height_thread + self.height_neck)))
+        )
+
+
+@dataclass(frozen=True)
+class HexNut(Item):
+    diam_thread: float
+    pitch: float
+
+    thickness: float
+    width: float
+
+    def __post_init__(self):
+        assert self.width > self.diam_thread
+
+    @property
+    def name(self):
+        return f"HexNut M{int(self.diam_thread)}-{self.pitch}"
+
+    @property
+    def role(self) -> Role:
+        return Role.CONNECTION
+
+    @property
+    def radius(self) -> float:
+        return self.width / math.sqrt(3)
+
+    def generate(self) -> Cq.Workplane:
+        result = (
+            Cq.Workplane("XY")
+            .sketch()
+            .regularPolygon(r=self.radius, n=6)
+            .circle(r=self.diam_thread/2, mode='s')
+            .finalize()
+            .extrude(self.thickness)
+        )
+        result.faces("<Z").tag("bot")
+        result.faces(">Z").tag("top")
+        result.copyWorkplane(Cq.Workplane('XY')).tagPlane("dirX", direction="+X")
+        return result
+
+    def cutting_face(self) -> Cq.Face:
+        return (
+            Cq.Sketch()
+            .regularPolygon(r=self.radius, n=6)
+            ._faces
+        )
+
+@dataclass(frozen=True)
+class Washer(Item):
+    diam_thread: float
+    diam_outer: float
+    thickness: float
+    material_name: Optional[float] = None
+
+    def __post_init__(self):
+        assert self.diam_outer > self.diam_thread
+    @property
+    def name(self):
+        suffix = (" " + self.material_name) if self.material_name else ""
+        return f"Washer M{int(self.diam_thread)}{suffix}"
+
+    @property
+    def role(self) -> Role:
+        return Role.CONNECTION
+
+    def generate(self) -> Cq.Workplane:
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.diam_outer/2,
+                height=self.thickness,
+            )
+            .faces(">Z")
+            .hole(self.diam_thread)
+        )
+        result.faces("<Z").tag("bot")
+        result.faces(">Z").tag("top")
+        return result

nhf/parts/fibre.py

@@ -0,0 +1,58 @@
+"""
+A fibre, for bearing tension
+"""
+import cadquery as Cq
+from dataclasses import dataclass
+import nhf.utils
+
+def tension_fibre(
+        length: float,
+        hole_diam: float,
+        hole_twist: float=0,
+        thickness: float=0.5) -> Cq.Workplane:
+    """
+    A fibre which holds tension, with an eyes on each end.
+
+    """
+    eye_female = Cq.Solid.makeTorus(
+        radius1=hole_diam/2 + thickness/2,
+        radius2=thickness/2,
+        dir=(1,0,0),
+    )
+    hole_length_male = hole_diam * 2.5
+    hole_height_male = hole_diam * 1.2
+    eye_male = Cq.Solid.makeBox(
+        length=hole_length_male + thickness * 2,
+        width=thickness,
+        height=hole_height_male + thickness * 2,
+    ).located(
+        Cq.Location((-hole_length_male/2-thickness, -thickness/2, -hole_height_male/2-thickness))
+    ).cut(Cq.Solid.makeBox(
+        length=hole_length_male,
+        width=thickness,
+        height=hole_height_male,
+    ).located(Cq.Location((-hole_length_male/2, -thickness/2, -hole_height_male/2))))
+    height = length - hole_diam - thickness
+    assert height > 0, "String is too short to support the given hole sizes"
+    h1 = length/2 - hole_diam/2 - thickness/2
+    h2 = length/2 - hole_height_male - thickness/2
+    result = (
+        Cq.Workplane('XY')
+        .cylinder(
+            radius=thickness/2,
+            height=h1,
+            centered=(True, True, False),
+        )
+        .copyWorkplane(Cq.Workplane('YX'))
+        .cylinder(
+            radius=thickness/2,
+            height=h2,
+            centered=(True, True, False),
+        )
+        .union(eye_female.located(Cq.Location((0, 0,length/2))))
+        .union(eye_male.located(Cq.Location((0, 0,-length/2+hole_height_male/2+thickness/2), (0,0,1), hole_twist)))
+    )
+    result.copyWorkplane(Cq.Workplane(Cq.Plane(origin=(0,0,length/2), normal=(1,0,0)))).tagPlane("female")
+    conn1_normal, _ = (Cq.Location((0,0,0),(0,0,1),hole_twist) * Cq.Location((1,0,0))).toTuple()
+    result.copyWorkplane(Cq.Workplane(Cq.Plane(origin=(0,0,-length/2), normal=conn1_normal))).tagPlane("male")
+    return result

nhf/parts/handle.py

@@ -0,0 +1,385 @@
+"""
+This schematics file contains all designs related to tool handles
+"""
+from dataclasses import dataclass, field
+from typing import Union, Optional
+import cadquery as Cq
+import nhf.parts.metric_threads as metric_threads
+import nhf.utils
+
+class Mount:
+    """
+    Describes the internal connection between two cylinders
+    """
+
+    def diam_insertion_internal(self) -> float:
+        """
+        Diameter of the internal cavity in the insertion
+        """
+    def diam_connector_external(self) -> float:
+        """
+        Diameter of the external size of the connector
+        """
+    def external_thread(self, length: float) -> Cq.Shape:
+        """
+        Generates the external connector
+        """
+    def internal_thread(self, length: float) -> Cq.Shape:
+        """
+        Generates the internal connector
+        """
+
+@dataclass
+class ThreadedMount(Mount):
+
+    pitch: float = 3
+
+    # Major diameter of the internal threads, following ISO metric screw thread
+    # standard. This determines the wall thickness of the insertion.
+    diam_threading: float = 27
+
+    def diam_insertion_internal(self) -> float:
+        r = metric_threads.metric_thread_major_radius(
+            self.diam_threading,
+            self.pitch,
+            internal=True)
+        return r * 2
+    def diam_connector_external(self) -> float:
+        r = metric_threads.metric_thread_minor_radius(
+            self.diam_threading,
+            self.pitch)
+        return r * 2
+
+    def external_thread(self, length: float):
+        return metric_threads.external_metric_thread(
+            self.diam_threading,
+            self.pitch,
+            length,
+            top_lead_in=True)
+    def internal_thread(self, length: float):
+        return metric_threads.internal_metric_thread(
+            self.diam_threading,
+            self.pitch,
+            length)
+
+@dataclass
+class BayonetMount(Mount):
+    """
+    Bayonet type connection
+    """
+    diam_outer: float = 30
+    diam_inner: float = 27
+
+    # Angular span (in degrees) of the slider
+    pin_span: float = 15
+    pin_height: float = 5
+    # Wall at the bottom of the slot
+    gap: float = 3
+
+    # Angular span (in degrees) of the slot
+    slot_span: float = 90
+
+    # Number of pins equally distributed along a circle
+    n_pin: int = 2
+
+
+    def __post_init__(self):
+        assert self.diam_outer > self.diam_inner
+        assert self.n_pin * self.slot_span < 360
+        assert self.slot_span > self.pin_span
+
+    def diam_insertion_internal(self) -> float:
+        return self.diam_outer
+    def diam_connector_external(self) -> float:
+        return self.diam_inner
+
+    def external_thread(self, length: float):
+        assert length > self.pin_height + self.gap
+        pin = (
+            Cq.Workplane('XY')
+            .cylinder(
+                height=self.pin_height,
+                radius=self.diam_outer / 2,
+                angle=self.pin_span,
+                centered=(True, True, False))
+            .copyWorkplane(Cq.Workplane('XY'))
+            .cylinder(
+                height=self.pin_height,
+                radius=self.diam_inner / 2,
+                centered=(True, True, False),
+                combine="cut")
+            .val()
+        )
+        result = (
+            Cq.Workplane('XY')
+            .workplane(offset=self.gap)
+            .polarArray(radius=0, startAngle=0, angle=360, count=self.n_pin)
+            .eachpoint(lambda loc: pin.located(loc), combine='a')
+            .clean()
+        )
+        return result
+    def internal_thread(self, length: float):
+        assert length > self.pin_height + self.gap
+        slot = (
+            Cq.Workplane('XY')
+            .cylinder(
+                height=length - self.gap,
+                radius=self.diam_outer / 2,
+                angle=self.pin_span,
+                centered=(True, True, False)
+            )
+            .copyWorkplane(Cq.Workplane('XY'))
+            .cylinder(
+                height=self.pin_height,
+                radius=self.diam_outer / 2,
+                angle=self.slot_span,
+                centered=(True, True, False)
+            )
+            .val()
+        )
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                height=length,
+                radius=self.diam_outer / 2,
+                centered=(True, True, False),
+            )
+            .copyWorkplane(Cq.Workplane('XY'))
+            .workplane(offset=self.gap)
+            .polarArray(radius=0, startAngle=self.slot_span, angle=360, count=self.n_pin)
+            .cutEach(lambda loc: slot.located(loc))
+            .clean()
+            .copyWorkplane(Cq.Workplane('XY'))
+            .cylinder(
+                height=length,
+                radius=self.diam_inner / 2,
+                centered=(True, True, False),
+                combine="cut"
+            )
+        )
+        return result
+
+
+@dataclass
+class Handle:
+    """
+    Characteristic of a tool handle
+
+    This assumes the handle segment material does not have threads. Each segment
+    attaches to two insertions, which have threads on the inside. A connector
+    has threads on the outside and mounts two insertions.
+
+    Note that all the radial sizes are diameters (in mm).
+    """
+
+    # Outer and inner radii for the handle usually come in standard sizes
+    diam: float = 38
+    diam_inner: float = 33
+
+    mount: Optional[Mount] = field(default_factory=lambda: ThreadedMount())
+
+    # Internal cavity diameter. This determines the wall thickness of the connector
+    diam_connector_internal: float = 18.0
+
+    # If set to true, do not generate the connections
+    simplify_geometry: bool = True
+
+    # Length for the rim on the female connector
+    rim_length: float = 5
+
+    insertion_length: float = 30
+
+    # Amount by which the connector goes into the segment
+    connector_length: float = 60
+
+    def __post_init__(self):
+        assert self.diam > self.diam_inner, "Material thickness cannot be <= 0"
+        if self.mount:
+            assert self.diam_inner > self.mount.diam_insertion_internal(), "Threading radius is too big"
+            assert self.mount.diam_insertion_internal() >= self.mount.diam_connector_external()
+            assert self.mount.diam_connector_external() > self.diam_connector_internal, "Internal diameter is too large"
+        assert self.insertion_length > self.rim_length
+
+    def segment(self, length: float):
+        result = (
+            Cq.Workplane()
+            .cylinder(
+                radius=self.diam / 2,
+                height=length)
+            .faces(">Z")
+            .hole(self.diam_inner)
+        )
+        result.faces("<Z").tag("mate1")
+        result.faces(">Z").tag("mate2")
+        return result
+
+    def insertion(self, holes=[]):
+        """
+        This type of mount is used to connect two handlebar pieces. Each handlebar
+        piece is a tube which cannot be machined, so the mount connects to the
+        handle by glue.
+
+        Tags:
+        * lip: Co-planar Mates to the rod
+        * mate: Mates to the connector
+
+        WARNING: A tolerance lower than the defualt (maybe 5e-4) is required for
+        STL export.
+
+        Set `holes` to the heights for drilling holes into the model for resin
+        to flow out.
+        """
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.diam_inner / 2,
+                height=self.insertion_length - self.rim_length,
+                centered=[True, True, False])
+        )
+        result.faces(">Z").tag("rim")
+        if self.rim_length > 0:
+            result = (
+                result.faces(">Z")
+                .workplane()
+                .circle(self.diam / 2)
+                .extrude(self.rim_length)
+                .faces(">Z")
+                .hole(self.mount.diam_insertion_internal())
+            )
+        result.faces(">Z").tag("mate")
+        result.copyWorkplane(Cq.Workplane('XY')).tagPlane("dir", "+X")
+        if not self.simplify_geometry:
+            thread = self.mount.internal_thread(self.insertion_length).val()
+            result = result.union(thread)
+        for h in holes:
+            cyl = Cq.Solid.makeCylinder(
+                radius=2,
+                height=self.diam * 2,
+                pnt=(-self.diam, 0, h),
+                dir=(1, 0, 0))
+            result = result.cut(cyl)
+        return result
+
+    def connector(self, solid: bool = True):
+        """
+        Tags:
+        * mate{1,2}: Mates to the connector
+
+        WARNING: A tolerance lower than the defualt (maybe 2e-4) is required for
+        STL export.
+        """
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.diam / 2,
+                height=self.connector_length,
+            )
+        )
+        for (tag, selector) in [("mate1", "<Z"), ("mate2", ">Z")]:
+            result.faces(selector).tag(tag)
+            result = (
+                result
+                .faces(selector)
+                .workplane()
+                .circle(self.mount.diam_connector_external() / 2)
+                .extrude(self.insertion_length)
+            )
+        if not solid:
+            result = result.faces(">Z").hole(self.diam_connector_internal)
+        if not self.simplify_geometry:
+            thread = self.mount.external_thread(self.insertion_length).val()
+            result = (
+                result
+                .union(
+                    thread
+                    .located(Cq.Location((0, 0, -self.connector_length))))
+                .union(
+                    thread
+                    .rotate((0,0,0), (1,0,0), angleDegrees=180)
+                    .located(Cq.Location((0, 0, self.connector_length))))
+            )
+        result.copyWorkplane(Cq.Workplane('XY')).tagPlane("dir", "+X")
+        return result
+
+    def one_side_connector(self, height=None):
+        if height is None:
+            height = self.rim_length
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.diam / 2,
+                height=height,
+                centered=(True, True, False)
+            )
+        )
+        result.faces(">Z").tag("mate")
+        result.faces("<Z").tag("base")
+        result = (
+            result
+            .faces(">Z")
+            .workplane()
+            .circle(self.mount.diam_connector_external() / 2)
+            .extrude(self.insertion_length)
+        )
+        result.copyWorkplane(Cq.Workplane('XY')).tagPlane("dir", "+X")
+        if not self.simplify_geometry:
+            thread = self.mount.external_thread(self.insertion_length).val()
+            result = (
+                result
+                .union(
+                    thread
+                    # Avoids collision in some mating cases
+                    .rotate((0,0,0), (1,0,0), angleDegrees=180)
+                    .located(Cq.Location((0, 0, height + self.insertion_length))))
+            )
+        return result
+
+    def threaded_core(self, length):
+        """
+        Generates a threaded core for unioning with other components
+        """
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.mount.diam_connector_external / 2,
+                height=length,
+                centered=(True, True, False),
+            )
+        )
+        result.faces(">Z").tag("mate")
+        result.faces("<Z").tag("base")
+        if not self.simplify_geometry:
+            thread = self.mount.external_thread(length=length).val()
+            result = (
+                result
+                .union(thread)
+            )
+        return result
+
+    def connector_insertion_assembly(self):
+        connector_color = Cq.Color(0.8,0.8,0.5,0.3)
+        insertion_color = Cq.Color(0.7,0.7,0.7,0.3)
+        result = (
+            Cq.Assembly()
+            .add(self.connector(), name="c", color=connector_color)
+            .add(self.insertion(), name="i1", color=insertion_color)
+            .add(self.insertion(), name="i2", color=insertion_color)
+            .constrain("c?mate1", "i1?mate", "Plane")
+            .constrain("c?mate2", "i2?mate", "Plane")
+            .constrain("c?dir", "i1?dir", "Axis")
+            .constrain("c?dir", "i2?dir", "Axis")
+            .solve()
+        )
+        return result
+    def connector_one_side_insertion_assembly(self):
+        connector_color = Cq.Color(0.8,0.8,0.5,0.3)
+        insertion_color = Cq.Color(0.7,0.7,0.7,0.3)
+        result = (
+            Cq.Assembly()
+            .add(self.insertion(), name="i", color=connector_color)
+            .add(self.one_side_connector(), name="c", color=insertion_color)
+            .constrain("i?mate", "c?mate", "Plane")
+            .constrain("c?dir", "i?dir", "Axis")
+            .solve()
+        )
+        return result

nhf/parts/item.py

@@ -0,0 +1,67 @@
+from typing import Union, Optional
+from collections import Counter
+from dataclasses import dataclass
+import cadquery as Cq
+from nhf.materials import Role, KEY_ROLE, KEY_ITEM
+
+@dataclass(frozen=True)
+class Item:
+    """
+    A pre-fabricated item
+    """
+    mass: float
+
+    #@property
+    #def mass(self) -> float:
+    #    """
+    #    Mass, in grams
+    #    """
+    #    return self._mass
+
+    #@mass.setter
+    #def mass(self, value):
+    #    assert value >= 0, "Mass cannot be negative"
+    #    self._mass = value
+
+    @property
+    def name(self) -> str:
+        pass
+
+    @property
+    def role(self) -> Optional[Role]:
+        return None
+
+    def generate(self, **kwargs) -> Union[Cq.Solid, Cq.Assembly, Cq.Workplane]:
+        """
+        Creates an assembly for this item. Subclass should implement this
+        """
+        return Cq.Assembly()
+
+    def assembly(self, **kwargs) -> Cq.Assembly:
+        """
+        Interface for creating assembly with the necessary metadata
+        """
+        a = self.generate(**kwargs)
+        if isinstance(a, Cq.Workplane) or isinstance(a, Cq.Solid):
+            a = Cq.Assembly(a)
+        if role := self.role:
+            a.metadata[KEY_ROLE] = role
+            a.color = role.color_avg()
+        assert isinstance(a, Cq.Assembly)
+        assert KEY_ITEM not in a.metadata
+        a.metadata[KEY_ITEM] = self
+        return a
+
+    @staticmethod
+    def count(a: Cq.Assembly) -> Counter:
+        """
+        Counts the number of items
+        """
+        occ = Counter()
+        for _, obj in a.traverse():
+            if KEY_ITEM not in obj.metadata:
+                continue
+            item = obj.metadata[KEY_ITEM]
+            assert isinstance(item, Item)
+            occ[item.name] += 1
+        return occ

nhf/parts/joints.py

@@ -0,0 +1,431 @@
+from dataclasses import dataclass, field
+from typing import Optional
+import math
+import cadquery as Cq
+from nhf.parts.springs import TorsionSpring
+from nhf import Role
+import nhf.utils
+
+TOL = 1e-6
+
+@dataclass(frozen=True)
+class HirthJoint:
+    """
+    A Hirth joint attached to a cylindrical base
+    """
+
+    # r
+    radius: float = 60
+    # r_i
+    radius_inner: float = 40
+    base_height: float = 20
+    n_tooth: float = 16
+    # h_o
+    tooth_height: float = 16
+
+    def __post_init__(self):
+        # Ensures tangent doesn't blow up
+        assert self.n_tooth >= 5
+        assert self.radius > self.radius_inner
+
+    @property
+    def tooth_angle(self):
+        return 360 / self.n_tooth
+
+    @property
+    def total_height(self):
+        return self.base_height + self.tooth_height
+
+    @property
+    def joint_height(self):
+        return 2 * self.base_height + self.tooth_height
+
+
+    def generate(self, is_mated=False, tol=0.01):
+        """
+        is_mated: If set to true, rotate the teeth so they line up at 0 degrees.
+
+        FIXME: Mate is not exact when number of tooth is low
+        """
+        phi = math.radians(self.tooth_angle)
+        alpha = 2 * math.atan(self.radius / self.tooth_height * math.tan(phi/2))
+        #alpha = math.atan(self.radius * math.radians(180 / self.n_tooth) / self.tooth_height)
+        gamma = math.radians(90 / self.n_tooth)
+        # Tooth half height
+        l = self.radius * math.cos(gamma)
+        a = self.radius * math.sin(gamma)
+        t = a / math.tan(alpha / 2)
+        beta = math.asin(t / l)
+        dx = self.tooth_height * math.tan(alpha / 2)
+        profile = (
+            Cq.Workplane('YZ')
+            .polyline([
+                (0, 0),
+                (dx, self.tooth_height),
+                (-dx, self.tooth_height),
+            ])
+            .close()
+            .extrude(-self.radius)
+            .val()
+            .rotate((0, 0, 0), (0, 1, 0), math.degrees(beta))
+            .moved(Cq.Location((0, 0, self.base_height)))
+        )
+        core = Cq.Solid.makeCylinder(
+            radius=self.radius_inner,
+            height=self.tooth_height,
+            pnt=(0, 0, self.base_height),
+        )
+        angle_offset = self.tooth_angle / 2 if is_mated else 0
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.radius,
+                height=self.base_height + self.tooth_height,
+                centered=(True, True, False))
+            .faces(">Z")
+            .tag("bore")
+            .cut(core)
+            .polarArray(
+                radius=self.radius,
+                startAngle=angle_offset,
+                angle=360,
+                count=self.n_tooth)
+            .cutEach(
+                lambda loc: profile.moved(loc),
+            )
+        )
+        (
+            result
+            .polyline([
+                (0, 0, self.base_height),
+                (0, 0, self.base_height + self.tooth_height)
+            ], forConstruction=True)
+            .tag("mate")
+        )
+        (
+            result
+            .polyline([(0, 0, 0), (1, 0, 0)], forConstruction=True)
+            .tag("dirX")
+        )
+        (
+            result
+            .polyline([(0, 0, 0), (0, 1, 0)], forConstruction=True)
+            .tag("dirY")
+        )
+        return result
+
+    def add_constraints(self,
+                        assembly: Cq.Assembly,
+                        parent: str,
+                        child: str,
+                        offset: int = 0):
+        angle = offset * self.tooth_angle
+        (
+            assembly
+            .constrain(f"{parent}?mate", f"{child}?mate", "Plane")
+            .constrain(f"{parent}?dirX", f"{child}?dirX",
+                       "Axis", param=angle)
+            .constrain(f"{parent}?dirY", f"{child}?dirX",
+                       "Axis", param=90 - angle)
+        )
+
+    def assembly(self, offset: int = 1):
+        """
+        Generate an example assembly
+        """
+        tab = (
+            Cq.Workplane('XY')
+            .box(100, 10, 2, centered=False)
+        )
+        obj1 = (
+            self.generate()
+            .faces(tag="bore")
+            .cboreHole(
+                diameter=10,
+                cboreDiameter=20,
+                cboreDepth=3)
+            .union(tab)
+        )
+        obj2 = (
+            self.generate(is_mated=True)
+            .union(tab)
+        )
+        result = (
+            Cq.Assembly()
+            .addS(obj1, name="obj1", role=Role.PARENT)
+            .addS(obj2, name="obj2", role=Role.CHILD)
+        )
+        self.add_constraints(
+            result,
+            parent="obj1",
+            child="obj2",
+            offset=offset)
+        return result.solve()
+
+@dataclass
+class TorsionJoint:
+    """
+    This jonit consists of a rider puck on a track puck. IT is best suited if
+    the radius has to be small and vertical space is abundant.
+
+    The rider part consists of:
+    1. A cylinderical base
+    2. A annular extrusion with the same radius as the base, but with slots
+        carved in
+    3. An annular rider
+
+    The track part consists of:
+    1. A cylindrical base
+    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(
+        mass=float('nan'),
+        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
+    radius_rider: float = 38
+    track_disk_height: float = 10
+    rider_disk_height: float = 8
+
+    radius_axle: float = 6
+
+    # If true, cover the spring hole. May make it difficult to insert the spring
+    # considering the stiffness of torsion spring steel.
+    spring_hole_cover_track: bool = False
+    spring_hole_cover_rider: bool = False
+
+    groove_radius_outer: float = 35
+    groove_radius_inner: float = 20
+    # Gap on inner groove to ease movement
+    groove_inner_gap: float = 0.2
+    groove_depth: float = 5
+    rider_gap: float = 1
+    rider_n_slots: float = 4
+
+    # Degrees of the first and last rider slots
+    rider_slot_begin: float = 0
+    rider_slot_span: float = 90
+
+
+    def __post_init__(self):
+        assert self.radius_track > self.groove_radius_outer
+        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"
+        assert self.groove_depth < self.spring.height - self.spring.thickness * 2
+        if self.rider_n_slots == 1:
+            assert self.rider_slot_span == 0.0, "Non-zero span is impossible with multiple riders"
+
+    @property
+    def total_height(self):
+        """
+        Total height counting from bottom to top
+        """
+        return self.track_disk_height + self.rider_disk_height + self.spring.height
+
+    @property
+    def radius(self):
+        """
+        Maximum radius of this joint
+        """
+        return max(self.radius_rider, self.radius_track)
+
+    def _slot_polygon(self, flip: bool=False):
+        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),
+            (0, r1),
+        ]
+    def _directrix(self, height, theta=0):
+        c, s = math.cos(theta), math.sin(theta)
+        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]]`
+        return [
+            (-s * r2,         c * r2, height),
+            (c * l - s * r2, s * l + c * r2, height),
+        ]
+
+    def track(self):
+        # TODO: Cover outer part of track only. Can we do this?
+        groove_profile = (
+            Cq.Sketch()
+            .circle(self.radius_track)
+            .circle(self.groove_radius_outer, mode='s')
+            .circle(self.groove_radius_inner, mode='a')
+            .circle(self.spring.radius, mode='s')
+        )
+        spring_hole_profile = (
+            Cq.Sketch()
+            .circle(self.radius_track)
+            .circle(self.spring.radius, mode='s')
+        )
+        slot_height = self.spring.thickness
+        if not self.spring_hole_cover_track:
+            slot_height += self.groove_depth
+        slot = (
+            Cq.Workplane('XY')
+            .sketch()
+            .polygon(self._slot_polygon(flip=False))
+            .finalize()
+            .extrude(slot_height)
+            .val()
+        )
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.radius_track,
+                height=self.track_disk_height,
+                centered=(True, True, False))
+            .faces('>Z')
+            .tag("spring")
+            .placeSketch(spring_hole_profile)
+            .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')
+            .placeSketch(groove_profile)
+            .extrude(self.groove_depth)
+            .faces('>Z')
+            .hole(self.radius_axle * 2)
+            .cut(slot.moved(Cq.Location((0, 0, self.track_disk_height))))
+        )
+        result.faces("<Z").tag("bot")
+        # Insert directrix
+        result.polyline(self._directrix(self.track_disk_height),
+                        forConstruction=True).tag("dir")
+        return result
+
+    def rider(self, rider_slot_begin=None, reverse_directrix_label=False):
+        if not rider_slot_begin:
+            rider_slot_begin = self.rider_slot_begin
+        def slot(loc):
+            wire = Cq.Wire.makePolygon(self._slot_polygon(flip=False))
+            face = Cq.Face.makeFromWires(wire)
+            return face.located(loc)
+        wall_profile = (
+            Cq.Sketch()
+            .circle(self.radius_rider, mode='a')
+            .circle(self.spring.radius, mode='s')
+            .parray(
+                r=0,
+                a1=rider_slot_begin,
+                da=self.rider_slot_span,
+                n=self.rider_n_slots)
+            .each(slot, mode='s')
+            #.circle(self._radius_wall, mode='a')
+        )
+        contact_profile = (
+            Cq.Sketch()
+            .circle(self.groove_radius_outer, mode='a')
+            .circle(self.groove_radius_inner + self.groove_inner_gap, mode='s')
+        )
+        if not self.spring_hole_cover_rider:
+            contact_profile = (
+                contact_profile
+                .parray(
+                    r=0,
+                    a1=rider_slot_begin,
+                    da=self.rider_slot_span,
+                    n=self.rider_n_slots)
+                .each(slot, mode='s')
+                .reset()
+            )
+            #.circle(self._radius_wall, mode='a')
+        middle_height = self.spring.height - self.groove_depth - self.rider_gap - self.spring.thickness
+        result = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.radius_rider,
+                height=self.rider_disk_height,
+                centered=(True, True, False))
+            .faces('>Z')
+            .tag("spring")
+            .workplane()
+            .placeSketch(wall_profile)
+            .extrude(middle_height)
+            .faces(tag="spring")
+            .workplane()
+            # The top face might not be in one piece.
+            .workplane(offset=middle_height)
+            .placeSketch(contact_profile)
+            .extrude(self.groove_depth + self.rider_gap)
+            .faces(tag="spring")
+            .workplane()
+            .circle(self.spring.radius_inner)
+            .extrude(self.spring.height)
+            .faces("<Z")
+            .workplane()
+            .hole(self.radius_axle * 2)
+        )
+        theta_begin = -math.radians(rider_slot_begin)
+        theta_span = math.radians(self.rider_slot_span)
+        if self.rider_n_slots <= 1:
+            theta_step = 0
+        elif abs(math.remainder(self.rider_slot_span, 360)) < TOL:
+            theta_step = theta_span / self.rider_n_slots
+        else:
+            theta_step = theta_span / (self.rider_n_slots - 1)
+        for i in range(self.rider_n_slots):
+            theta = theta_begin - i * theta_step
+            j = self.rider_n_slots - i - 1 if reverse_directrix_label else i
+            result.polyline(self._directrix(self.rider_disk_height, theta),
+                            forConstruction=True).tag(f"dir{j}")
+        return result
+
+    def rider_track_assembly(self, directrix: int = 0, deflection: float = 0):
+        rider = self.rider()
+        track = self.track()
+        spring = self.spring.assembly(deflection=deflection)
+        result = (
+            Cq.Assembly()
+            .addS(spring, name="spring", role=Role.DAMPING)
+            .addS(track, name="track", role=Role.PARENT)
+            .addS(rider, name="rider", role=Role.CHILD)
+        )
+        TorsionJoint.add_constraints(
+            result,
+            rider="rider", track="track", spring="spring",
+            directrix=directrix)
+        return result.solve()
+
+    @staticmethod
+    def add_constraints(assembly: Cq.Assembly,
+                        spring: str,
+                        rider: Optional[str] = None,
+                        track: Optional[str] = None,
+                        directrix: int = 0):
+        """
+        Add the necessary constraints to a RT assembly
+        """
+        if track:
+            (
+                assembly
+                .constrain(f"{track}?spring", f"{spring}?top", "Plane")
+                .constrain(f"{track}?dir", f"{spring}?dir_top",
+                           "Axis", param=0)
+            )
+        if rider:
+            (
+                assembly
+                .constrain(f"{rider}?spring", f"{spring}?bot", "Plane")
+                .constrain(f"{rider}?dir{directrix}", f"{spring}?dir_bot",
+                           "Axis", param=0)
+            )

nhf/parts/metric_threads.py

@@ -0,0 +1,422 @@
+# Copyright (c) 2020-2024, Nerius Anthony Landys.  All rights reserved.
+#   neri-engineering 'at' protonmail.com
+#   https://svn.code.sf.net/p/nl10/code/cq-code/common/metric_threads.py
+# This file is public domain.  Use it for any purpose, including commercial
+# applications.  Attribution would be nice, but is not required.  There is no
+# warranty of any kind, including its correctness, usefulness, or safety.
+#
+# Simple code example to create meshing M3x0.5 threads:
+###############################################################################
+#
+#     male   = external_metric_thread(3.0, 0.5, 4.0, z_start= -0.85,
+#                                     top_lead_in=True)
+#
+#     # Please note that the female thread is meant for a hole which has
+#     # radius equal to metric_thread_major_radius(3.0, 0.5, internal=True),
+#     # which is in fact very slightly larger than a 3.0 diameter hole.
+#
+#     female = internal_metric_thread(3.0, 0.5, 1.5,
+#                                     bottom_chamfer=True, base_tube_od= 4.5)
+#
+###############################################################################
+# Left hand threads can be created by employing one of the "mirror" operations.
+# Thanks for taking the time to understand and use this code!
+
+import math
+import cadquery as cq
+
+###############################################################################
+# The functions which have names preceded by '__' are not meant to be called
+# externally; the remaining functions are written with the intention that they
+# will be called by external code.  The first section of code consists of
+# lightweight helper functions; the meat and potatoes of this library is last.
+###############################################################################
+
+# Return value is in degrees, and currently it's fixed at 30.  Essentially this
+# results in a typical 60 degree equilateral triangle cutting bit for threads.
+def metric_thread_angle():
+    return 30
+
+# Helper func. to make code more intuitive and succinct.  Degrees --> radians.
+def __deg2rad(degrees):
+    return degrees * math.pi / 180
+
+# In the absence of flat thread valley and flattened thread tip, returns the
+# amount by which the thread "triangle" protrudes outwards (radially) from base
+# cylinder in the case of external thread, or the amount by which the thread
+# "triangle" protrudes inwards from base tube in the case of internal thread.
+def metric_thread_perfect_height(pitch):
+    return pitch / (2 * math.tan(__deg2rad(metric_thread_angle())))
+
+# Up the radii of internal (female) thread in order to provide a little bit of
+# wiggle room around male thread.  Right now input parameter 'diameter' is
+# ignored.  This function is only used for internal/female threads.  Currently
+# there is no practical way to adjust the male/female thread clearance besides
+# to manually edit this function.  This design route was chosen for the sake of
+# code simplicity.
+def __metric_thread_internal_radius_increase(diameter, pitch):
+    return 0.1 * metric_thread_perfect_height(pitch)
+
+# Returns the major radius of thread, which is always the greater of the two.
+def metric_thread_major_radius(diameter, pitch, internal=False):
+    return (__metric_thread_internal_radius_increase(diameter, pitch) if
+            internal else 0.0) + (diameter / 2)
+
+# What portion of the total pitch is taken up by the angled thread section (and
+# not the squared off valley and tip).  The remaining portion (1 minus ratio)
+# will be divided equally between the flattened valley and flattened tip.
+def __metric_thread_effective_ratio():
+    return 0.7
+
+# Returns the minor radius of thread, which is always the lesser of the two.
+def metric_thread_minor_radius(diameter, pitch, internal=False):
+    return (metric_thread_major_radius(diameter, pitch, internal)
+            - (__metric_thread_effective_ratio() *
+               metric_thread_perfect_height(pitch)))
+
+# What the major radius would be if the cuts were perfectly triangular, without
+# flat spots in the valleys and without flattened tips.
+def metric_thread_perfect_major_radius(diameter, pitch, internal=False):
+    return (metric_thread_major_radius(diameter, pitch, internal)
+            + ((1.0 - __metric_thread_effective_ratio()) *
+               metric_thread_perfect_height(pitch) / 2))
+
+# What the minor radius would be if the cuts were perfectly triangular, without
+# flat spots in the valleys and without flattened tips.
+def metric_thread_perfect_minor_radius(diameter, pitch, internal=False):
+    return (metric_thread_perfect_major_radius(diameter, pitch, internal)
+            - metric_thread_perfect_height(pitch))
+
+# Returns the lead-in and/or chamfer distance along the z axis of rotation.
+# The lead-in/chamfer only depends on the pitch and is made with the same angle
+# as the thread, that being 30 degrees offset from radial.
+def metric_thread_lead_in(pitch, internal=False):
+    return (math.tan(__deg2rad(metric_thread_angle()))
+            * (metric_thread_major_radius(256.0, pitch, internal)
+               - metric_thread_minor_radius(256.0, pitch, internal)))
+
+# Returns the width of the flat spot in thread valley of a standard thread.
+# This is also equal to the width of the flat spot on thread tip, on a standard
+# thread.
+def metric_thread_relief(pitch):
+    return (1.0 - __metric_thread_effective_ratio()) * pitch / 2
+
+
+###############################################################################
+# A few words on modules external_metric_thread() and internal_metric_thread().
+# The parameter 'z_start' is added as a convenience in order to make the male
+# and female threads align perfectly.  When male and female threads are created
+# having the same diameter, pitch, and n_starts (usually 1), then so long as
+# they are not translated or rotated (or so long as they are subjected to the
+# same exact translation and rotation), they will intermesh perfectly,
+# regardless of the value of 'z_start' used on each.  This is in order that
+# assemblies be able to depict perfectly aligning threads.
+
+# Generates threads with base cylinder unless 'base_cylinder' is overridden.
+# Please note that 'use_epsilon' is activated by default, which causes a slight
+# budge in the minor radius, inwards, so that overlaps would be created with
+# inner cylinders.  (Does not affect thread profile outside of cylinder.)
+###############################################################################
+def external_metric_thread(diameter,  # Required parameter, e.g. 3.0 for M3x0.5
+                           pitch,     # Required parameter, e.g. 0.5 for M3x0.5
+                           length,    # Required parameter, e.g. 2.0
+                           z_start=0.0,
+                           n_starts=1,
+                           bottom_lead_in=False, # Lead-in is at same angle as
+                           top_lead_in   =False, # thread, namely 30 degrees.
+                           bottom_relief=False, # Add relief groove to start or
+                           top_relief   =False, # end of threads (shorten).
+                           force_outer_radius=-1.0, # Set close to diameter/2.
+                           use_epsilon=True, # For inner cylinder overlap.
+                           base_cylinder=True, # Whether to include base cyl.
+                           cyl_extend_bottom=-1.0,
+                           cyl_extend_top=-1.0,
+                           envelope=False): # Draw only envelope, don't cut.
+
+    cyl_extend_bottom = max(0.0, cyl_extend_bottom)
+    cyl_extend_top    = max(0.0, cyl_extend_top)
+
+    z_off             = (1.0 - __metric_thread_effective_ratio()) * pitch / 4
+    t_start           = z_start
+    t_length          = length
+    if bottom_relief:
+        t_start       = t_start  + (2 * z_off)
+        t_length      = t_length - (2 * z_off)
+    if top_relief:
+        t_length      = t_length - (2 * z_off)
+    outer_r           = (force_outer_radius if (force_outer_radius > 0.0) else
+                         metric_thread_major_radius(diameter,pitch))
+    inner_r           = metric_thread_minor_radius(diameter,pitch)
+    epsilon           = 0
+    inner_r_adj       = inner_r
+    inner_z_budge     = 0
+    if use_epsilon:
+        epsilon       = (z_off/3) / math.tan(__deg2rad(metric_thread_angle()))
+        inner_r_adj   = inner_r - epsilon
+        inner_z_budge = math.tan(__deg2rad(metric_thread_angle())) * epsilon
+
+    if envelope:
+        threads = cq.Workplane("XZ")
+        threads = threads.moveTo(inner_r_adj, -pitch)
+        threads = threads.lineTo(outer_r, -pitch)
+        threads = threads.lineTo(outer_r, t_length + pitch)
+        threads = threads.lineTo(inner_r_adj, t_length + pitch)
+        threads = threads.close()
+        threads = threads.revolve()
+
+    else: # Not envelope, cut the threads.
+        wire = cq.Wire.makeHelix(pitch=pitch*n_starts,
+                                 height=t_length+pitch,
+                                 radius=inner_r)
+        wire = wire.translate((0,0,-pitch/2))
+        wire = wire.rotate(startVector=(0,0,0), endVector=(0,0,1),
+                           angleDegrees=360*(-pitch/2)/(pitch*n_starts))
+        d_mid = ((metric_thread_major_radius(diameter,pitch) - outer_r)
+                 * math.tan(__deg2rad(metric_thread_angle())))
+        thread = cq.Workplane("XZ")
+        thread = thread.moveTo(inner_r_adj, -pitch/2 + z_off - inner_z_budge)
+        thread = thread.lineTo(outer_r, -(z_off + d_mid))
+        thread = thread.lineTo(outer_r, z_off + d_mid)
+        thread = thread.lineTo(inner_r_adj, pitch/2 - z_off + inner_z_budge)
+        thread = thread.close()
+        thread = thread.sweep(wire, isFrenet=True)
+        threads = thread
+        for addl_start in range(1, n_starts):
+            # TODO: Incremental/cumulative rotation may not be as accurate as
+            #       keeping 'thread' intact and rotating it by correct amount
+            #       on each iteration.  However, changing the code in that
+            #       regard may disrupt the delicate nature of workarounds
+            #       with repsect to quirks in the underlying B-rep library.
+            thread = thread.rotate(axisStartPoint=(0,0,0),
+                                   axisEndPoint=(0,0,1),
+                                   angleDegrees=360/n_starts)
+            threads = threads.union(thread)
+
+    square_shave = cq.Workplane("XY")
+    square_shave = square_shave.box(length=outer_r*3, width=outer_r*3,
+                                    height=pitch*2, centered=True)
+    square_shave = square_shave.translate((0,0,-pitch)) # Because centered.
+    # Always cut the top and bottom square.  Otherwise things don't play nice.
+    threads = threads.cut(square_shave)
+
+    if bottom_lead_in:
+        delta_r = outer_r - inner_r
+        rise = math.tan(__deg2rad(metric_thread_angle())) * delta_r
+        lead_in = cq.Workplane("XZ")
+        lead_in = lead_in.moveTo(inner_r - delta_r, -rise)
+        lead_in = lead_in.lineTo(outer_r + delta_r, 2 * rise)
+        lead_in = lead_in.lineTo(outer_r + delta_r, -pitch - rise)
+        lead_in = lead_in.lineTo(inner_r - delta_r, -pitch - rise)
+        lead_in = lead_in.close()
+        lead_in = lead_in.revolve()
+        threads = threads.cut(lead_in)
+
+    # This was originally a workaround to the anomalous B-rep computation where
+    # the top of base cylinder is flush with top of threads, without the use of
+    # lead-in.  It turns out that preferring the use of the 'render_cyl_early'
+    # strategy alleviates other problems as well.
+    render_cyl_early = (base_cylinder and ((not top_relief) and
+                                           (not (cyl_extend_top > 0.0)) and
+                                           (not envelope)))
+    render_cyl_late = (base_cylinder and (not render_cyl_early))
+    if render_cyl_early:
+        cyl = cq.Workplane("XY")
+        cyl = cyl.circle(radius=inner_r)
+        cyl = cyl.extrude(until=length+pitch+cyl_extend_bottom)
+        # Make rotation of cylinder consistent with non-workaround case.
+        cyl = cyl.rotate(axisStartPoint=(0,0,0), axisEndPoint=(0,0,1),
+                         angleDegrees=-(360*t_start/(pitch*n_starts)))
+        cyl = cyl.translate((0,0,-t_start+(z_start-cyl_extend_bottom)))
+        threads = threads.union(cyl)
+
+    # Next, make cuts at the top.
+    square_shave = square_shave.translate((0,0,pitch*2+t_length))
+    threads = threads.cut(square_shave)
+
+    if top_lead_in:
+        delta_r = outer_r - inner_r
+        rise = math.tan(__deg2rad(metric_thread_angle())) * delta_r
+        lead_in = cq.Workplane("XZ")
+        lead_in = lead_in.moveTo(inner_r - delta_r, t_length + rise)
+        lead_in = lead_in.lineTo(outer_r + delta_r, t_length - (2 * rise))
+        lead_in = lead_in.lineTo(outer_r + delta_r, t_length + pitch + rise)
+        lead_in = lead_in.lineTo(inner_r - delta_r, t_length + pitch + rise)
+        lead_in = lead_in.close()
+        lead_in = lead_in.revolve()
+        threads = threads.cut(lead_in)
+
+    # Place the threads into position.
+    threads = threads.translate((0,0,t_start))
+    if (not envelope):
+        threads = threads.rotate(axisStartPoint=(0,0,0), axisEndPoint=(0,0,1),
+                                 angleDegrees=360*t_start/(pitch*n_starts))
+
+    if render_cyl_late:
+        cyl = cq.Workplane("XY")
+        cyl = cyl.circle(radius=inner_r)
+        cyl = cyl.extrude(until=length+cyl_extend_bottom+cyl_extend_top)
+        cyl = cyl.translate((0,0,z_start-cyl_extend_bottom))
+        threads = threads.union(cyl)
+
+    return threads
+
+
+###############################################################################
+# Generates female threads without a base tube, unless 'base_tube_od' is set to
+# something which is sufficiently greater than 'diameter' parameter.  Please
+# note that 'use_epsilon' is activated by default, which causes a slight budge
+# in the major radius, outwards, so that overlaps would be created with outer
+# tubes.  (Does not affect thread profile inside of tube or beyond extents.)
+###############################################################################
+def internal_metric_thread(diameter,  # Required parameter, e.g. 3.0 for M3x0.5
+                           pitch,     # Required parameter, e.g. 0.5 for M3x0.5
+                           length,    # Required parameter, e.g. 2.0.
+                           z_start=0.0,
+                           n_starts=1,
+                           bottom_chamfer=False, # Chamfer is at same angle as
+                           top_chamfer   =False, # thread, namely 30 degrees.
+                           bottom_relief=False, # Add relief groove to start or
+                           top_relief   =False, # end of threads (shorten).
+                           use_epsilon=True, # For outer cylinder overlap.
+                           # The base tube outer diameter must be sufficiently
+                           # large for tube to be rendered.  Otherwise ignored.
+                           base_tube_od=-1.0,
+                           tube_extend_bottom=-1.0,
+                           tube_extend_top=-1.0,
+                           envelope=False): # Draw only envelope, don't cut.
+
+    tube_extend_bottom = max(0.0, tube_extend_bottom)
+    tube_extend_top    = max(0.0, tube_extend_top)
+
+    z_off              = (1.0 - __metric_thread_effective_ratio()) * pitch / 4
+    t_start            = z_start
+    t_length           = length
+    if bottom_relief:
+        t_start        = t_start  + (2 * z_off)
+        t_length       = t_length - (2 * z_off)
+    if top_relief:
+        t_length       = t_length - (2 * z_off)
+    outer_r            = metric_thread_major_radius(diameter,pitch,
+                                                    internal=True)
+    inner_r            = metric_thread_minor_radius(diameter,pitch,
+                                                    internal=True)
+    epsilon            = 0
+    outer_r_adj        = outer_r
+    outer_z_budge      = 0
+    if use_epsilon:
+        # High values of 'epsilon' sometimes cause entire starts to disappear.
+        epsilon        = (z_off/5) / math.tan(__deg2rad(metric_thread_angle()))
+        outer_r_adj    = outer_r + epsilon
+        outer_z_budge  = math.tan(__deg2rad(metric_thread_angle())) * epsilon
+
+    if envelope:
+        threads = cq.Workplane("XZ")
+        threads = threads.moveTo(outer_r_adj, -pitch)
+        threads = threads.lineTo(inner_r, -pitch)
+        threads = threads.lineTo(inner_r, t_length + pitch)
+        threads = threads.lineTo(outer_r_adj, t_length + pitch)
+        threads = threads.close()
+        threads = threads.revolve()
+
+    else: # Not envelope, cut the threads.
+        wire = cq.Wire.makeHelix(pitch=pitch*n_starts,
+                                 height=t_length+pitch,
+                                 radius=inner_r)
+        wire = wire.translate((0,0,-pitch/2))
+        wire = wire.rotate(startVector=(0,0,0), endVector=(0,0,1),
+                           angleDegrees=360*(-pitch/2)/(pitch*n_starts))
+        thread = cq.Workplane("XZ")
+        thread = thread.moveTo(outer_r_adj, -pitch/2 + z_off - outer_z_budge)
+        thread = thread.lineTo(inner_r, -z_off)
+        thread = thread.lineTo(inner_r, z_off)
+        thread = thread.lineTo(outer_r_adj, pitch/2 - z_off + outer_z_budge)
+        thread = thread.close()
+        thread = thread.sweep(wire, isFrenet=True)
+        threads = thread
+        for addl_start in range(1, n_starts):
+            # TODO: Incremental/cumulative rotation may not be as accurate as
+            #       keeping 'thread' intact and rotating it by correct amount
+            #       on each iteration.  However, changing the code in that
+            #       regard may disrupt the delicate nature of workarounds
+            #       with repsect to quirks in the underlying B-rep library.
+            thread = thread.rotate(axisStartPoint=(0,0,0),
+                                   axisEndPoint=(0,0,1),
+                                   angleDegrees=360/n_starts)
+            threads = threads.union(thread)
+        # Rotate so that the external threads would align.
+        threads = threads.rotate(axisStartPoint=(0,0,0), axisEndPoint=(0,0,1),
+                                 angleDegrees=180/n_starts)
+
+    square_len = max(outer_r*3, base_tube_od*1.125)
+    square_shave = cq.Workplane("XY")
+    square_shave = square_shave.box(length=square_len, width=square_len,
+                                    height=pitch*2, centered=True)
+    square_shave = square_shave.translate((0,0,-pitch)) # Because centered.
+    # Always cut the top and bottom square.  Otherwise things don't play nice.
+    threads = threads.cut(square_shave)
+
+    if bottom_chamfer:
+        delta_r = outer_r - inner_r
+        rise = math.tan(__deg2rad(metric_thread_angle())) * delta_r
+        chamfer = cq.Workplane("XZ")
+        chamfer = chamfer.moveTo(inner_r - delta_r, 2 * rise)
+        chamfer = chamfer.lineTo(outer_r + delta_r, -rise)
+        chamfer = chamfer.lineTo(outer_r + delta_r, -pitch - rise)
+        chamfer = chamfer.lineTo(inner_r - delta_r, -pitch - rise)
+        chamfer = chamfer.close()
+        chamfer = chamfer.revolve()
+        threads = threads.cut(chamfer)
+
+    # This was originally a workaround to the anomalous B-rep computation where
+    # the top of base tube is flush with top of threads w/o the use of chamfer.
+    # This is now being made consistent with the 'render_cyl_early' strategy in
+    # external_metric_thread() whereby we prefer the "render early" plan of
+    # action even in cases where a top chamfer or lead-in is used.
+    render_tube_early = ((base_tube_od > (outer_r * 2)) and
+                         (not top_relief) and
+                         (not (tube_extend_top > 0.0)) and
+                         (not envelope))
+    render_tube_late = ((base_tube_od > (outer_r * 2)) and
+                        (not render_tube_early))
+    if render_tube_early:
+        tube = cq.Workplane("XY")
+        tube = tube.circle(radius=base_tube_od/2)
+        tube = tube.circle(radius=outer_r)
+        tube = tube.extrude(until=length+pitch+tube_extend_bottom)
+        # Make rotation of cylinder consistent with non-workaround case.
+        tube = tube.rotate(axisStartPoint=(0,0,0), axisEndPoint=(0,0,1),
+                           angleDegrees=-(360*t_start/(pitch*n_starts)))
+        tube = tube.translate((0,0,-t_start+(z_start-tube_extend_bottom)))
+        threads = threads.union(tube)
+
+    # Next, make cuts at the top.
+    square_shave = square_shave.translate((0,0,pitch*2+t_length))
+    threads = threads.cut(square_shave)
+
+    if top_chamfer:
+        delta_r = outer_r - inner_r
+        rise = math.tan(__deg2rad(metric_thread_angle())) * delta_r
+        chamfer = cq.Workplane("XZ")
+        chamfer = chamfer.moveTo(inner_r - delta_r, t_length - (2 * rise))
+        chamfer = chamfer.lineTo(outer_r + delta_r, t_length + rise)
+        chamfer = chamfer.lineTo(outer_r + delta_r, t_length + pitch + rise)
+        chamfer = chamfer.lineTo(inner_r - delta_r, t_length + pitch + rise)
+        chamfer = chamfer.close()
+        chamfer = chamfer.revolve()
+        threads = threads.cut(chamfer)
+
+    # Place the threads into position.
+    threads = threads.translate((0,0,t_start))
+    if (not envelope):
+        threads = threads.rotate(axisStartPoint=(0,0,0), axisEndPoint=(0,0,1),
+                                 angleDegrees=360*t_start/(pitch*n_starts))
+
+    if render_tube_late:
+        tube = cq.Workplane("XY")
+        tube = tube.circle(radius=base_tube_od/2)
+        tube = tube.circle(radius=outer_r)
+        tube = tube.extrude(until=length+tube_extend_bottom+tube_extend_top)
+        tube = tube.translate((0,0,z_start-tube_extend_bottom))
+        threads = threads.union(tube)
+
+    return threads

nhf/parts/planar.py

@@ -0,0 +1,36 @@
+"""
+Operations on planar geometry (usually used for laser cutting parts)
+"""
+import math
+from typing import Tuple
+import cadquery as Cq
+
+def extrude_with_markers(
+        sketch: Cq.Sketch,
+        thickness: float,
+        tags: list[Tuple[str, Cq.Location]],
+        reverse: bool = False):
+    """
+    Extrudes a sketch and place tags on the sketch for mating.
+
+    Each tag is of the format `(name, loc)`, where the (must be 2d) location's
+    angle is specifies in degrees counterclockwise from +X. Two marks are
+    generated for each `name`, "{name}" for the location (with normal) and
+    "{name}_dir" for the directrix specified by the angle.
+
+    This simulates a process of laser cutting and bonding (for wood and acrylic)
+    """
+    result = (
+        Cq.Workplane('XY')
+        .placeSketch(sketch)
+        .extrude(thickness)
+    )
+    plane = result.faces("<Z" if reverse else ">Z").workplane()
+    sign = -1 if reverse else 1
+    for tag, p in tags:
+        (x, y), angle = p.to2d()
+        theta = sign * math.radians(angle)
+        direction = (math.cos(theta), math.sin(theta), 0)
+        plane.moveTo(x, sign * y).tagPlane(tag)
+        plane.moveTo(x, sign * y).tagPlane(f"{tag}_dir", direction)
+    return result

nhf/parts/springs.py

@@ -0,0 +1,79 @@
+import math
+from typing import Optional
+from dataclasses import dataclass
+import cadquery as Cq
+from nhf import Item, Role
+
+@dataclass(frozen=True)
+class TorsionSpring(Item):
+    """
+    A torsion spring with abridged geometry (since sweep is slow)
+    """
+    # Outer radius
+    radius: float = 12.0
+    height: float = 20.0
+    thickness: float = 2.0
+
+    # 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 name(self) -> str:
+        return f"TorsionSpring-{int(self.radius)}-{int(self.height)}"
+
+    @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) -> Cq.Workplane:
+        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")
+
+        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

nhf/parts/test.py

@@ -0,0 +1,125 @@
+import unittest
+import cadquery as Cq
+from nhf.checks import binary_intersection, pairwise_intersection
+from nhf.parts import joints, handle, metric_threads, springs
+import nhf.parts.fasteners as fasteners
+
+class TestFasteners(unittest.TestCase):
+
+    def test_hex_nut(self):
+        width = 18.9
+        height = 9.8
+        item = fasteners.HexNut(
+            mass=float('nan'),
+            diam_thread=12.0,
+            pitch=1.75,
+            thickness=9.8,
+            width=width,
+        )
+        obj = item.generate()
+        self.assertEqual(len(obj.vals()), 1)
+        bbox = obj.val().BoundingBox()
+        self.assertAlmostEqual(bbox.xlen, width)
+        self.assertAlmostEqual(bbox.zlen, height)
+
+class TestJoints(unittest.TestCase):
+
+    def test_joint_hirth(self):
+        j = joints.HirthJoint()
+        obj = j.generate()
+        self.assertIsInstance(
+            obj.val().solids(), Cq.Solid,
+            msg="Hirth joint must be in one piece")
+
+    def test_joints_hirth_assembly(self):
+        for n_tooth in [16, 20, 24]:
+            with self.subTest(n_tooth=n_tooth):
+                j = joints.HirthJoint()
+                assembly = j.assembly()
+                isect = binary_intersection(assembly)
+                self.assertLess(isect.Volume(), 1e-6,
+                                "Hirth joint assembly must not have intersection")
+
+    def torsion_joint_case(self, joint: joints.TorsionJoint, slot: int):
+        assert 0 <= slot and slot < joint.rider_n_slots
+        assembly = joint.rider_track_assembly(slot)
+        bbox = assembly.toCompound().BoundingBox()
+        self.assertAlmostEqual(bbox.zlen, joint.total_height)
+        self.assertAlmostEqual(bbox.xlen, joint.radius * 2)
+        self.assertAlmostEqual(bbox.ylen, joint.radius * 2)
+        self.assertEqual(pairwise_intersection(assembly), [])
+
+    def test_torsion_joint(self):
+        j = joints.TorsionJoint()
+        for slot in range(j.rider_n_slots):
+            with self.subTest(slot=slot, right_handed=False):
+                self.torsion_joint_case(j, slot)
+    def test_torsion_joint_right_handed(self):
+        j = joints.TorsionJoint(springs.TorsionSpring(mass=float('nan'), right_handed=True))
+        for slot in range(j.rider_n_slots):
+            with self.subTest(slot=slot, right_handed=True):
+                self.torsion_joint_case(j, slot)
+    def test_torsion_joint_covered(self):
+        j = joints.TorsionJoint(
+            spring_hole_cover_track=True,
+            spring_hole_cover_rider=True,
+        )
+        self.torsion_joint_case(j, 1)
+    def test_torsion_joint_slot(self):
+        j = joints.TorsionJoint(
+            rider_slot_begin=90,
+        )
+        self.torsion_joint_case(j, 1)
+
+
+
+class TestHandle(unittest.TestCase):
+
+    def test_threaded_collision(self):
+        h = handle.Handle(mount=handle.ThreadedMount())
+        assembly = h.connector_insertion_assembly()
+        self.assertEqual(pairwise_intersection(assembly), [])
+    def test_threaded_assembly(self):
+        h = handle.Handle(mount=handle.ThreadedMount())
+        assembly = h.connector_insertion_assembly()
+        bbox = assembly.toCompound().BoundingBox()
+        self.assertAlmostEqual(bbox.xlen, h.diam)
+        self.assertAlmostEqual(bbox.ylen, h.diam)
+    def test_threaded_one_sided_insertion(self):
+        h = handle.Handle(mount=handle.ThreadedMount())
+        assembly = h.connector_one_side_insertion_assembly()
+        bbox = assembly.toCompound().BoundingBox()
+        self.assertAlmostEqual(bbox.xlen, h.diam)
+        self.assertAlmostEqual(bbox.ylen, h.diam)
+        self.assertEqual(pairwise_intersection(assembly), [])
+    def test_bayonet_collision(self):
+        h = handle.Handle(mount=handle.BayonetMount())
+        assembly = h.connector_insertion_assembly()
+        self.assertEqual(pairwise_intersection(assembly), [])
+    def test_bayonet_assembly(self):
+        h = handle.Handle(mount=handle.BayonetMount())
+        assembly = h.connector_insertion_assembly()
+        bbox = assembly.toCompound().BoundingBox()
+        self.assertAlmostEqual(bbox.xlen, h.diam)
+        self.assertAlmostEqual(bbox.ylen, h.diam)
+
+    def test_bayonet_one_sided_insertion(self):
+        h = handle.Handle(mount=handle.BayonetMount())
+        assembly = h.connector_one_side_insertion_assembly()
+        bbox = assembly.toCompound().BoundingBox()
+        self.assertAlmostEqual(bbox.xlen, h.diam)
+        self.assertAlmostEqual(bbox.ylen, h.diam)
+        self.assertEqual(pairwise_intersection(assembly), [])
+
+class TestMetricThreads(unittest.TestCase):
+
+    def test_major_radius(self):
+        major = 3.0
+        t = metric_threads.external_metric_thread(major, 0.5, 4.0, z_start=-0.85, top_lead_in=True)
+        bbox = t.val().BoundingBox()
+        self.assertAlmostEqual(bbox.xlen, major, places=3)
+        self.assertAlmostEqual(bbox.ylen, major, places=3)
+
+
+if __name__ == '__main__':
+    unittest.main()

nhf/test.py

@@ -0,0 +1,287 @@
+"""
+Unit tests for tooling
+"""
+from dataclasses import dataclass
+import math
+import unittest
+import cadquery as Cq
+from nhf.build import Model, target
+from nhf.parts.item import Item
+import nhf.checks
+import nhf.geometry
+import nhf.utils
+
+# Color presets for testing purposes
+color_parent = Cq.Color(0.7, 0.7, 0.5, 0.5)
+color_child = Cq.Color(0.5, 0.7, 0.7, 0.5)
+
+def makeSphere(r: float) -> Cq.Solid:
+    """
+    Makes a full sphere. The default function makes a hemisphere
+    """
+    return Cq.Solid.makeSphere(r, angleDegrees1=-90)
+
+@dataclass(frozen=True)
+class MassBall(Item):
+    """
+    A ball with fixed mass
+    """
+    radius: float = 0.2
+
+    @property
+    def name(self) -> str:
+        return f"MassBall {self.mass}"
+    def generate(self) -> Cq.Solid:
+        return makeSphere(self.radius)
+
+
+class BuildScaffold(Model):
+
+    def __init__(self):
+        super().__init__(name="scaffold")
+
+    @target(name="obj1")
+    def o1(self):
+        return Cq.Solid.makeBox(10, 10, 10)
+
+    def o2(self):
+        return Cq.Solid.makeCylinder(10, 20)
+
+class TestBuild(unittest.TestCase):
+
+    def test_build_scaffold(self):
+        s = BuildScaffold()
+        names = ["obj1"]
+        self.assertEqual(s.target_names, names)
+        self.assertEqual(s.check_all(), len(names))
+
+class TestChecks(unittest.TestCase):
+
+    def intersect_test_case(self, offset):
+        assembly = (
+            Cq.Assembly()
+            .add(Cq.Solid.makeBox(10, 10, 10),
+                 name="c1",
+                 loc=Cq.Location((0, 0, 0)))
+            .add(Cq.Solid.makeBox(10, 10, 10),
+                 name="c2",
+                 loc=Cq.Location((0, 0, offset)))
+        )
+        coll = nhf.checks.pairwise_intersection(assembly)
+        if -10 < offset and offset < 10:
+            self.assertEqual(len(coll), 1)
+        else:
+            self.assertEqual(coll, [])
+
+    def test_intersect(self):
+        for offset in [9, 10, 11, -10]:
+            with self.subTest(offset=offset):
+                self.intersect_test_case(offset)
+
+class TestGeometry(unittest.TestCase):
+
+    def test_min_radius_contraction_span_pos(self):
+        sl = 50.0
+        dc = 112.0
+        do = dc + sl
+        theta = math.radians(60.0)
+        r, phi = nhf.geometry.min_radius_contraction_span_pos(do, dc, theta)
+        with self.subTest(state='open'):
+            x = r * math.cos(phi)
+            y = r * math.sin(phi)
+            d = math.sqrt((x - r) ** 2 + y ** 2)
+            self.assertAlmostEqual(d, do)
+        with self.subTest(state='closed'):
+            x = r * math.cos(phi - theta)
+            y = r * math.sin(phi - theta)
+            d = math.sqrt((x - r) ** 2 + y ** 2)
+            self.assertAlmostEqual(d, dc)
+    def test_min_tangent_contraction_span_pos(self):
+        sl = 50.0
+        dc = 112.0
+        do = dc + sl
+        theta = math.radians(60.0)
+        r, phi, rp = nhf.geometry.min_tangent_contraction_span_pos(do, dc, theta)
+        with self.subTest(state='open'):
+            x = r * math.cos(phi)
+            y = r * math.sin(phi)
+            d = math.sqrt((x - rp) ** 2 + y ** 2)
+            self.assertAlmostEqual(d, do)
+        with self.subTest(state='closed'):
+            x = r * math.cos(phi - theta)
+            y = r * math.sin(phi - theta)
+            d = math.sqrt((x - rp) ** 2 + y ** 2)
+            self.assertAlmostEqual(d, dc)
+    def test_contraction_span_pos_from_radius(self):
+        sl = 50.0
+        dc = 112.0
+        do = dc + sl
+        r = 70.0
+        theta = math.radians(60.0)
+        for smaller in [False, True]:
+            with self.subTest(smaller=smaller):
+                r, phi, rp = nhf.geometry.contraction_span_pos_from_radius(do, dc, r=r, theta=theta, smaller=smaller)
+                with self.subTest(state='open'):
+                    x = r * math.cos(phi)
+                    y = r * math.sin(phi)
+                    d = math.sqrt((x - rp) ** 2 + y ** 2)
+                    self.assertAlmostEqual(d, do)
+                with self.subTest(state='closed'):
+                    x = r * math.cos(phi - theta)
+                    y = r * math.sin(phi - theta)
+                    d = math.sqrt((x - rp) ** 2 + y ** 2)
+                    self.assertAlmostEqual(d, dc)
+    def test_contraction_span_pos_from_radius_2(self):
+        sl = 40.0
+        dc = 170.0
+        do = dc + sl
+        r = 50.0
+        theta = math.radians(120.0)
+        for smaller in [False, True]:
+            with self.subTest(smaller=smaller):
+                r, phi, rp = nhf.geometry.contraction_span_pos_from_radius(do, dc, r=r, theta=theta, smaller=smaller)
+                with self.subTest(state='open'):
+                    x = r * math.cos(phi)
+                    y = r * math.sin(phi)
+                    d = math.sqrt((x - rp) ** 2 + y ** 2)
+                    self.assertAlmostEqual(d, do)
+                with self.subTest(state='closed'):
+                    x = r * math.cos(phi - theta)
+                    y = r * math.sin(phi - theta)
+                    d = math.sqrt((x - rp) ** 2 + y ** 2)
+                    self.assertAlmostEqual(d, dc)
+
+
+class TestUtils(unittest.TestCase):
+
+    def test_2d_orientation(self):
+        l1 = Cq.Location.from2d(1.2, 0)
+        l2 = Cq.Location.from2d(0, 0, 90)
+        l3 = l2 * l1
+        (x, y), r = l3.to2d()
+        self.assertAlmostEqual(x, 0)
+        self.assertAlmostEqual(y, 1.2)
+        self.assertAlmostEqual(r, 90)
+
+    def test_2d_planar(self):
+        l1 = Cq.Location.from2d(1.2, 4.5, 67)
+        l2 = Cq.Location.from2d(98, 5.4, 36)
+        l3 = Cq.Location.from2d(10, 10, 0)
+        l = l3 * l2 * l1
+        self.assertTrue(l.is2d())
+
+    def test_tag_point(self):
+        """
+        A board with 3 holes of unequal sizes. Each hole is marked
+        """
+        p4x, p4y = 5, 5
+        p3x, p3y = 0, 0
+        p2x, p2y = -5, 0
+        board = (
+            Cq.Workplane('XY')
+            .box(15, 15, 5)
+            .faces("<Z")
+            .workplane()
+            .pushPoints([(p4x, p4y)])
+            .hole(4, depth=2)
+            .pushPoints([(p3x, p3y)])
+            .hole(3, depth=1.5)
+            .pushPoints([(p2x, p2y)])
+            .hole(2, depth=1)
+        )
+        board.moveTo(p4x, p4y).tagPoint("h4")
+        board.moveTo(p3x, p3y).tagPoint("h3")
+        board.moveTo(p2x, p2y).tagPoint("h2")
+
+        assembly = (
+            Cq.Assembly()
+            .add(board, name="board", color=color_parent)
+            .add(makeSphere(2), name="s4", color=color_child)
+            .add(makeSphere(1.5), name="s3", color=color_child)
+            .add(makeSphere(1), name="s2", color=color_child)
+            .constrain("board?h4", "s4", "Point")
+            .constrain("board?h3", "s3", "Point")
+            .constrain("board?h2", "s2", "Point")
+            .solve()
+        )
+        self.assertEqual(nhf.checks.pairwise_intersection(assembly), [])
+        bbox = assembly.toCompound().BoundingBox()
+        self.assertAlmostEqual(bbox.xlen, 15)
+        self.assertAlmostEqual(bbox.ylen, 15)
+        self.assertAlmostEqual(bbox.zlen, 7)
+
+    def test_tag_plane(self):
+        p4x, p4y = 5, 5
+        p3x, p3y = 0, 0
+        p2x, p2y = -5, 0
+        board = (
+            Cq.Workplane('XY')
+            .box(15, 15, 5)
+            .faces("<Z")
+            .workplane()
+            .pushPoints([(p4x, p4y)])
+            .hole(4, depth=2)
+            .pushPoints([(p3x, p3y)])
+            .hole(3, depth=1.5)
+            .pushPoints([(p2x, p2y)])
+            .hole(2, depth=1)
+        )
+        board.moveTo(p4x, p4y).tagPlane("h4")
+        board.moveTo(p3x, p3y).tagPlane("h3")
+        board.moveTo(p2x, p2y).tagPlane("h2")
+
+        def markedCylOf(r):
+            cyl = (
+                Cq.Workplane('XY')
+                .cylinder(radius=r, height=r)
+            )
+            cyl.faces("<Z").tag("mate")
+            return cyl
+
+        assembly = (
+            Cq.Assembly()
+            .add(board, name="board", color=color_parent)
+            .add(markedCylOf(2), name="c4", color=color_child)
+            .add(markedCylOf(1.5), name="c3", color=color_child)
+            .add(markedCylOf(1), name="c2", color=color_child)
+            .constrain("board?h4", "c4?mate", "Plane", param=0)
+            .constrain("board?h3", "c3?mate", "Plane", param=0)
+            .constrain("board?h2", "c2?mate", "Plane", param=0)
+            .solve()
+        )
+        self.assertEqual(nhf.checks.pairwise_intersection(assembly), [])
+        bbox = assembly.toCompound().BoundingBox()
+        self.assertAlmostEqual(bbox.xlen, 15)
+        self.assertAlmostEqual(bbox.ylen, 15)
+        self.assertAlmostEqual(bbox.zlen, 5)
+
+    def test_abs_location(self):
+        box = Cq.Solid.makeBox(1, 1, 1)
+        assembly = (
+            Cq.Assembly()
+            .add(box, name="b1")
+            .add(box, name="b2", loc=Cq.Location((0,0,1)))
+            .add(box, name="b3", loc=Cq.Location((0,0,2)))
+        )
+        (x, y, z), _ = assembly.get_abs_location("b2@faces@>Y").toTuple()
+        self.assertAlmostEqual(x, 0.5)
+        self.assertAlmostEqual(y, 1)
+        self.assertAlmostEqual(z, 1.5)
+        (rx, ry, rz), _ = assembly.get_abs_direction("b2@faces@>Y").toTuple()
+        self.assertAlmostEqual(rx, 0)
+        self.assertAlmostEqual(ry, 1)
+        self.assertAlmostEqual(rz, 0)
+
+    def test_centre_of_mass(self):
+        assembly = (
+            Cq.Assembly()
+            .add(MassBall(mass=3).assembly(), name="s1", loc=Cq.Location((0, 0, 0)))
+            .add(MassBall(mass=7).assembly(), name="s2", loc=Cq.Location((0, 0, 10)))
+        )
+        com = assembly.centre_of_mass()
+        self.assertAlmostEqual(com.x, 0)
+        self.assertAlmostEqual(com.y, 0)
+        self.assertAlmostEqual(com.z, 7)
+
+if __name__ == '__main__':
+    unittest.main()

nhf/utils.py

@@ -0,0 +1,282 @@
+"""
+Utility functions for cadquery objects
+"""
+import functools
+import math
+from typing import Optional
+import cadquery as Cq
+from cadquery.occ_impl.solver import ConstraintSpec
+from nhf import Role
+from typing import Union, Tuple, cast
+from nhf.materials import KEY_ITEM, KEY_MATERIAL
+
+# Bug fixes
+def _subloc(self, name: str) -> Tuple[Cq.Location, str]:
+    """
+       Calculate relative location of an object in a subassembly.
+
+       Returns the relative positions as well as the name of the top assembly.
+       """
+
+    rv = Cq.Location()
+    obj = self.objects[name]
+    name_out = name
+
+    if obj not in self.children and obj is not self:
+        locs = []
+        while not obj.parent is self:
+            locs.append(obj.loc)
+            obj = cast(Cq.Assembly, obj.parent)
+            name_out = obj.name
+
+        rv = functools.reduce(lambda l1, l2: l2 * l1, locs)
+
+    return (rv, name_out)
+Cq.Assembly._subloc = _subloc
+
+### Vector arithmetic
+
+def location_sub(self: Cq.Location, rhs: Cq.Location) -> Cq.Vector:
+    (x1, y1, z1), _ = self.toTuple()
+    (x2, y2, z2), _ = rhs.toTuple()
+    return Cq.Vector(x1 - x2, y1 - y2, z1 - z2)
+Cq.Location.__sub__ = location_sub
+
+def from2d(x: float, y: float, rotate: float=0.0) -> Cq.Location:
+    return Cq.Location((x, y, 0), (0, 0, 1), rotate)
+Cq.Location.from2d = from2d
+
+def rot2d(angle: float) -> Cq.Location:
+    return Cq.Location((0, 0, 0), (0, 0, 1), angle)
+Cq.Location.rot2d = rot2d
+
+def is2d(self: Cq.Location) -> bool:
+    (_, _, z), (rx, ry, _) = self.toTuple()
+    return z == 0 and rx == 0 and ry == 0
+Cq.Location.is2d = is2d
+
+def to2d(self: Cq.Location) -> Tuple[Tuple[float, float], float]:
+    """
+    Returns position and angle
+    """
+    (x, y, z), (rx, ry, rz) = self.toTuple()
+    assert z == 0
+    assert rx == 0
+    assert ry == 0
+    return (x, y), rz
+Cq.Location.to2d = to2d
+
+def to2d_pos(self: Cq.Location) -> Tuple[float, float]:
+    """
+    Returns position and angle
+    """
+    (x, y), _ = self.to2d()
+    return x, y
+Cq.Location.to2d_pos = to2d_pos
+
+def to2d_rot(self: Cq.Location) -> float:
+    """
+    Returns position and angle
+    """
+    _, r = self.to2d()
+    return r
+Cq.Location.to2d_rot = to2d_rot
+
+
+def with_angle_2d(self: Cq.Location, angle: float) -> Tuple[float, float]:
+    """
+    Returns position and angle
+    """
+    x, y = self.to2d_pos()
+    return Cq.Location.from2d(x, y, angle)
+Cq.Location.with_angle_2d = with_angle_2d
+
+def flip_x(self: Cq.Location) -> Cq.Location:
+    (x, y), a = self.to2d()
+    return Cq.Location.from2d(-x, y, 90 - a)
+Cq.Location.flip_x = flip_x
+def flip_y(self: Cq.Location) -> Cq.Location:
+    (x, y), a = self.to2d()
+    return Cq.Location.from2d(x, -y, -a)
+Cq.Location.flip_y = flip_y
+
+def boolean(self: Cq.Sketch, obj, **kwargs) -> Cq.Sketch:
+    return (
+        self
+        .reset()
+        .push([(0, 0)])
+        .each(lambda _: obj, **kwargs)
+    )
+Cq.Sketch.boolean = boolean
+
+### Tags
+
+def tagPoint(self, tag: str):
+    """
+    Adds a vertex that can be used in `Point` constraints.
+    """
+    vertex = Cq.Vertex.makeVertex(0, 0, 0)
+    self.eachpoint(vertex.moved, useLocalCoordinates=True).tag(tag)
+
+Cq.Workplane.tagPoint = tagPoint
+
+def tagPlane(self, tag: str,
+             direction: Union[str, Cq.Vector, Tuple[float, float, float]] = '+Z'):
+    """
+    Adds a phantom `Cq.Edge` in the given location which can be referenced in a
+    `Axis`, `Point`, or `Plane` constraint.
+    """
+    if isinstance(direction, str):
+        x, y, z = 0, 0, 0
+        assert len(direction) == 2
+        sign, axis = direction
+        if axis in ('z', 'Z'):
+            z = 1
+        elif axis in ('y', 'Y'):
+            y = 1
+        elif axis in ('x', 'X'):
+            x = 1
+        else:
+            assert False, "Axis must be one of x,y,z"
+        if sign == '+':
+            sign = 1
+        elif sign == '-':
+            sign = -1
+        else:
+            assert False, "Sign must be one of +/-"
+        v = Cq.Vector(x, y, z) * sign
+    else:
+        v = Cq.Vector(direction)
+    edge = Cq.Edge.makeLine(v * (-1), v)
+    return self.eachpoint(edge.located, useLocalCoordinates=True).tag(tag)
+
+Cq.Workplane.tagPlane = tagPlane
+
+def make_sphere(r: float = 2) -> Cq.Solid:
+    """
+    Makes a full sphere. The default function makes a hemisphere
+    """
+    return Cq.Solid.makeSphere(r, angleDegrees1=-90)
+def make_arrow(size: float = 2) -> Cq.Workplane:
+    cone = Cq.Solid.makeCone(
+        radius1 = size,
+        radius2 = 0,
+        height=size)
+    result = (
+        Cq.Workplane("XY")
+        .cylinder(radius=size / 2, height=size, centered=(True, True, False))
+        .union(cone.located(Cq.Location((0, 0, size))))
+    )
+    result.faces("<Z").tag("dir_rev")
+    return result
+
+def to_marker_name(tag: str) -> str:
+    return tag.replace("?", "__T").replace("/", "__Z") + "_marker"
+
+COLOR_MARKER = Cq.Color(0, 1, 1, 1)
+
+def mark_point(self: Cq.Assembly,
+               tag: str,
+               size: float = 2,
+               color: Cq.Color = COLOR_MARKER) -> Cq.Assembly:
+    """
+    Adds a marker to make a point visible
+    """
+    name = to_marker_name(tag)
+    return (
+        self
+        .add(make_sphere(size), name=name, color=color)
+        .constrain(tag, name, "Point")
+    )
+
+Cq.Assembly.markPoint = mark_point
+
+def mark_plane(self: Cq.Assembly,
+               tag: str,
+               size: float = 2,
+               color: Cq.Color = COLOR_MARKER) -> Cq.Assembly:
+    """
+    Adds a marker to make a plane visible
+    """
+    name = to_marker_name(tag)
+    return (
+        self
+        .add(make_arrow(size), name=name, color=color)
+        .constrain(tag, f"{name}?dir_rev", "Plane", param=180)
+    )
+
+Cq.Assembly.markPlane = mark_plane
+
+def get_abs_location(self: Cq.Assembly,
+                     tag: str) -> Cq.Location:
+    """
+    Gets the location of a tag
+
+    BUG: Currently bugged. See `nhf/test.py` for example
+    """
+    name, shape = self._query(tag)
+    loc_self = Cq.Location(shape.Center())
+    loc_parent, _ = self._subloc(name)
+    loc = loc_parent * loc_self
+    return loc
+
+Cq.Assembly.get_abs_location = get_abs_location
+
+def get_abs_direction(self: Cq.Assembly,
+                      tag: str) -> Cq.Location:
+    """
+    Gets the location of a tag
+    """
+    name, shape = self._query(tag)
+    # Must match `cadquery.occ_impl.solver.ConstraintSpec._getAxis`
+    if isinstance(shape, Cq.Face):
+        vec_dir = shape.normalAt()
+    elif isinstance(shape, Cq.Edge) and shape.geomType() != "CIRCLE":
+        vec_dir = shape.tangentAt()
+    elif isinstance(shape, Cq.Edge) and shape.geomType() == "CIRCLE":
+        vec_dir = shape.normal()
+    else:
+        raise ValueError(f"Cannot construct Axis for {shape}")
+    loc_self = Cq.Location(vec_dir)
+    loc_parent, _ = self._subloc(name)
+    loc = loc_parent * loc_self
+    return loc
+Cq.Assembly.get_abs_direction = get_abs_direction
+
+
+# Tallying functions
+
+def assembly_this_mass(self: Cq.Assembly) -> Optional[float]:
+    """
+    Gets the mass of an assembly, without considering its components.
+    """
+    if item := self.metadata.get(KEY_ITEM):
+        return item.mass
+    elif material := self.metadata.get(KEY_MATERIAL):
+        vol = self.toCompound().Volume()
+        return (vol / 1000) * material.density
+    else:
+        return None
+
+def total_mass(self: Cq.Assembly) -> float:
+    """
+    Calculates the total mass in units of g
+    """
+    total = 0.0
+    for _, a in self.traverse():
+        if m := assembly_this_mass(a):
+            total += m
+    return total
+Cq.Assembly.total_mass = total_mass
+
+def centre_of_mass(self: Cq.Assembly) -> Optional[float]:
+    moment = Cq.Vector()
+    total = 0.0
+    for n, a in self.traverse():
+        if m := assembly_this_mass(a):
+            moment += m * a.toCompound().Center()
+            total += m
+    if total == 0.0:
+        return None
+    return moment / total
+Cq.Assembly.centre_of_mass = centre_of_mass