Smith

Smith is an Elixir CAD library. Build sketches, solids, and named assemblies with functions and pipelines, then export STEP, STL, and 3MF files. Models run in a standalone .exs script, a Livebook, or an existing Mix application.

Smith uses OCEx. The geometry engine is Open CASCADE Technology (OCCT) 7.9.3.

A rounded plate with a through hole, rendered by Smith in Livebook

A printable part in one script

Install the native toolkit using the installation guide, then save this as mount.exs:

Mix.install([{:smith, "~> 0.1.0"}])
alias Smith.Sketch

model =
  Sketch.rounded_rectangle(60, 40, 2)
  |> Sketch.cut([
    Sketch.circle(4, at: {-20, 0}),
    Sketch.circle(4, at: {20, 0})
  ])
  |> Smith.extrude(5)

{:ok, result} = Smith.evaluate(model)
{:ok, files} = Smith.export(result, "output", name: "mount", on_bed: true)
IO.puts(files.three_mf)

Run elixir mount.exs. The output bundle includes STEP, BREP, binary STL, and 3MF files, plus a report of the mesh and STEP checks. Every export gets a new directory; earlier exports remain available. 3MF contains printable geometry, without printer or slicer settings.

In an existing Mix project, add {:smith, "~> 0.1.0"} to deps/0. Smith requires Elixir 1.18+ and a supported native installation; see the installation guide for the tested OS/OTP combinations. No display server is required to model, mesh, or export.

Functions first

Recipes are immutable values. Construction makes no native calls; Smith.evaluate/1 builds the geometry. Reuse a sketch or body in multiple variants, name features with functions, and use ordinary comprehensions for repeated features:

hole_pattern = for x <- [-20, 20], y <- [-10, 10], do: Sketch.circle(2, at: {x, y})

plate =
  Sketch.rectangle(60, 40)
  |> Sketch.cut(hole_pattern)
  |> Smith.extrude(4)

side_plate = plate |> Smith.rotate({1, 0, 0}, 90) |> Smith.translate({0, 30, 0})

Distances are millimeters. Model transformations use world coordinates; sketch coordinates live in an explicit local plane. Shapes retain analytic surfaces until meshing. A recipe is your editable design; an evaluated BREP hash identifies its geometry, not its feature history.

Boxes, cylinders, cones, spheres, and tori accept at: {x, y, z} and per-axis alignment. For example, Smith.box(40, 20, 4, align: {:center, :center, :min}) centers the footprint with its bottom at Z=0. See primitive placement.

Parts that belong together

alias Smith.Assembly

assembly =
  Assembly.new(:bracket)
  |> Assembly.part(:base, plate, print: [on_bed: true])
  |> Assembly.part(:side, side_plate, print: [rotation: {{1, 0, 0}, -90}, on_bed: true])
  |> Assembly.reference(:electronics, Smith.box(20, 10, 6), position: {-10, -5, 4})

{:ok, result} = Smith.evaluate(assembly)
{:ok, files} = Smith.export(result, "output", name: "bracket")
IO.puts(files.print_pack)

Named parts have installed, print, and display placement. Reuse groups with Assembly.subassembly/4 and retrieve a descendant with a path such as Assembly.fetch(result, [:left, :base]). References stay out of printable files. A complete assembly export contains separate part bundles, assembly STEP, reference STEP, and a ZIP of printable STL/3MF pairs. The current manifest is updated after the part mesh checks and STEP round trips pass. See exporting for the exact checks and their limits.

Explore builds in Livebook

The Livebook guide shows each construction stage in its own rotatable preview and lets you download PNG images. Kino is optional: add it to the notebook's dependencies to enable Smith.Kino. Modeling and export remain independent of the notebook.

The drawing Livebook builds a counterbored plate, compares top/front/oblique views, and exports SVG/DXF alongside printable geometry.

Learn the library

Getting started: scripts, projects, parameters, and the first export.
Modeling: primitives, composition, transformations, selectors, and finishing.
Sketches and planes: alignment, cutouts, fillets, extrusion, revolve, and loft.
Extrusion extent and taper: symmetric depth, tapered walls and holes, and tilted end caps.
Curve projection: project onto surfaces, inspect multiple hits, and fill planar outlines.
Orthographic drawings: visible and hidden edges, view coordinates, and SVG/DXF export.
Mechanical parts: slots, recessed holes, mirrors, and measured selections.
Paths, lofts, and shells: selectors, curved sweeps, smooth transitions, and hollow parts.
Forming and cutting: draft, plane cuts, sections, surface offset, and thickening.
Assemblies: named parts, nested instances, references, and print placement.
Joints and poses: attachment frames, motion limits, and connected instances.
Exporting: formats, mesh settings, verification, and output manifests.
Livebook: visible build stages and downloadable images.
Errors and limits: evaluation failures, native execution, and supported scope.

Scope

Version 0.1 covers explicit dimensions, Boolean operations, edge and face selection, edge finishing, extrusion, revolution, ruled and smooth lofts, open-path sweeps, shelling with selected openings, draft, planar splits and sections, surface offset, and thickening. Sketches support lines, arcs, interpolated splines, and cutouts.

There is no sketch constraint solver, persistent topology naming, closed-linkage solver, or STEP product tree. Assembly joints provide directed rigid placement with explicit motion coordinates. Surface offsets follow 3D normals; planar sketch-outline offsets are not implemented. Thickening requires an open surface. Sketch subtraction retains one connected region. Loft and sweep sections cannot contain holes; sweep profiles must be placed explicitly. Shelling requires an opening.

OCEx serializes native operations on dirty CPU schedulers. Kernel calls are synchronous and cannot be forcibly cancelled; a native memory fault can terminate the BEAM. These limits are explained in the error guide. Export checks include mesh connectivity and volume agreement. They do not check design clearances, wall thickness, or printer settings.

Source is MIT licensed. OCCT is a separately installed dependency with its own license. See the repository for development, CI, release instructions, and the full deck clip and plant stand examples.

Working on Smith

This is a standalone repository. See development for local checks and releasing for this package's release steps.