A reusable part usually needs a small set of deliberate dimensions: its outline, fastener locations, clearances, and placement. Keep those dimensions in ordinary Elixir values and functions. Smith recipes compose without evaluating intermediate bodies.
Outlines and solid primitives
Sketch.rounded_rectangle(width, height, radius) rounds all four corners before applying cutouts. Sketch.slot(length, width) uses overall length, with semicircular ends of diameter width. Both use the same local on:, at:, and align: options as a rectangle. Equal slot length and width make a circle. A nonzero straight span must exceed the native 1.0e-7 mm edge tolerance.
Smith.sphere(radius) and Smith.torus(major_radius, minor_radius) default to centered bounds on all three axes. The torus lies around world Z; its major radius reaches the tube center, and its minor radius is the tube radius. Both support the standard world at: and three-axis align: options. Rotate the result for a different orientation. Tori must have major radius greater than minor radius by more than 1.0e-7 mm.
alias Smith.{Plane, Selector, Sketch}
outline =
Sketch.rounded_rectangle(60, 40, 4)
|> Sketch.cut(Sketch.slot(20, 6))
plate = Smith.extrude(outline, 8)
ring = Smith.torus(10, 2, align: {:center, :center, :min})
ball = Smith.sphere(3, at: {0, 0, 3})Holes and entry planes
Every hole specifies a diameter and exactly one extent: through: :all or depth: millimeters. A blind hole starts at the entry plane, travels along its negative normal, and leaves a flat floor. If the plane is outside the body, part of the specified depth is spent reaching the surface. Through-all instead spans the body's projected bounds in both directions, regardless of where the plane lies.
With on: :top, Smith selects the unique highest outward +Z planar face. Coordinates in at: {u, v} are offsets from that face's area centroid. Earlier asymmetric cuts can move that centroid. Use an explicit plane for a pattern with fixed design coordinates:
entry = Plane.xy(z: 8)
plate =
for x <- [-22, 22], y <- [-12, 12], reduce: plate do
model ->
Smith.countersink(model,
on: entry, at: {x, y}, diameter: 4,
sink_diameter: 8, angle: 90, through: :all
)
endCounterbores add bore_diameter: and bore_depth:. Countersinks add sink_diameter: and an included angle: in degrees, default 90. The recess diameter must exceed the pilot diameter. For a blind feature, total depth: includes the recess and must reach its bottom. A countersink's depth is (sink_diameter - diameter) / (2 * tan(angle / 2)).
plate =
plate
|> Smith.counterbore(on: entry, at: {0, -12}, diameter: 4,
bore_diameter: 8, bore_depth: 3, through: :all)
|> Smith.hole(on: entry, at: {0, 12}, diameter: 3, depth: 4)A pilot cut must remove material or evaluation fails with :hole_misses_body. Its recess must remove additional material or it fails with :recess_misses_body. Invalid extent/recess options return :invalid_options. Errors retain the feature name and recipe step in Smith.Error. These features specify geometry rather than a thread standard, drill-point angle, or automatic clearance allowance.
Select, sort, and inspect
Selector filters operate on the preceding selection. Length, radius, and area accept a numeric value or inclusive {minimum, maximum} range. The optional tolerance: defaults to 1.0e-7 in the property's units: mm for length/radius, mm² for area. Candidates with no reported radius do not match a radius filter.
{:ok, part} = Smith.evaluate(plate)
circular_edges = Selector.type(:circle) |> Selector.radius({1.5, 4})
{:ok, circles} = Smith.inspect_edges(part, circular_edges)
true = circles != []
largest_planes = Selector.type(:plane) |> Selector.sort_by(:area, :desc) |> Selector.take(2)
{:ok, faces} = Smith.inspect_faces(part, largest_planes)
true = length(faces) == 2inspect_edges/2 and inspect_faces/2 return maps containing a native :shape handle and geometry metadata, including world bounds. Edges also have a curve-parameter midpoint. Face centers are area centroids. These are not bounding-box centers. Query handles belong to the evaluated revision; retain and reevaluate selectors when the recipe changes.
sort_by/3 accepts length, area, radius, or a world axis. Missing radii sort last in either direction, and exact ties retain their incoming order. Kernel order is not a persistent identity. take/2 deliberately limits a selection and may discard ties; at_min/2 and at_max/2 retain all coordinate ties within 1.0e-7 mm.
horizontal = Selector.any_of([Selector.facing(:z), Selector.facing({:z, :negative})])
sides = Selector.type(:plane) |> Selector.exclude(horizontal)
{:ok, side_faces} = Smith.inspect_faces(part, sides)
true = side_faces != []Each union or exclusion branch starts with the preceding selection. Union preserves that selection's order and includes each candidate only once. An empty union selects nothing. Invalid nested queries fail even when an earlier filter selected no candidates. Predicates must return booleans; predicate exceptions propagate to the caller.
Mirror and export
A mirror returns the reflected recipe. Its plane can be :xy, :xz, :yz, or any positioned Smith.Plane. It preserves outward solid orientation and does not retain the original automatically. Use an assembly to keep both parts separately, or fuse/2 when touching copies should form one body.
alias Smith.Assembly
pair =
Assembly.new(:mechanical_pair)
|> Assembly.part(:left, plate, print: [on_bed: true])
|> Assembly.part(:right, Smith.mirror(plate, Plane.yz(x: 40)), print: [on_bed: true])
{:ok, pair_result} = Smith.evaluate(pair)
{:ok, files} = Smith.export(pair_result, "output", name: "mechanical-pair", angular_tolerance: 0.1)
files.print_packThe ZIP contains each part's STL and 3MF. Installed geometry remains in STEP; print placement affects the printable files. Export checks meshes and STEP round trips. Inspect wall thickness, fit, and print orientation for your own design. The mechanical parts Livebook shows each stage and checks the removed volume against independent formulas.