constraint-kit

constraint-kit turns plain-English mechanism descriptions into exact, manufacturable CAD: STEP files and real B-rep geometry, not a mesh. The LLM only decides which parts, which parameters, and what connects to what; parametric generators build exact B-rep solids and a deterministic mate kernel puts every part in place. The model never places a single vertex.

Results are checked, not just looked at, per the README: gears mesh because center distances come from module and teeth, mates are solved against named joint frames that survive parameter changes, collisions are caught by a bounding-box prefilter followed by an exact OpenCascade boolean clash check, and mechanisms are solved with Willis' equation for planetary mobility, SolveSpace for linkages, and a Z3 SMT solver for gear-train and tolerance synthesis.

The tool declines honestly when a request is outside its vocabulary, naming the gap instead of guessing: the README's example asks for a spiral bevel gear and gets back that only straight bevel gears are modeled. A physics tier adds linear elastostatics on a voxel grid using numpy and scipy only, verified against ground truth such as a cantilever reaching 95.7 to 98.5 percent of Timoshenko at 4 to 8 elements through the thickness; when the convergence sequence is not actually converging, it says so instead of fitting a confident number to noise.

The README's example run turns a plate with a spacer and a 24-tooth gear stacked on its boss into a 100 by 100 mm aluminum plate with a 4-bolt circle, a spacer, and a module-2 24-tooth steel spur gear seated with zero gap, emitting STEP, GLB, mass properties, a BOM, and a render.