Lab Hardware CAD

Design physical research hardware as parametric Python source, export STEP as the authoritative artifact, and verify the result both numerically and visually before anything is fabricated.

The hard part of lab hardware is almost never the geometry. It is that the part must mate with equipment whose dimensions are fixed by a published standard or a vendor drawing. A holder that is 0.5 mm too wide does not fit the plate reader; a channel with the wrong aspect ratio collapses during bonding; a mount whose bolt pattern is 25.4 mm instead of 25.0 mm will not reach the optical table. This skill exists to keep those numbers correct and checked.

When to use

Use for any request to design, model, or fabricate a physical part for a lab: chip, mold, mount, adapter, holder, rack, bracket, enclosure, jig, fixture, arena, or maze. Also use to inspect or modify an existing STEP file.

Do not use for finite-element analysis, computational fluid dynamics, molecular structure, or scientific plotting. Those are different skills.

Setup

uv venv --python 3.12 .venv-labcad
uv pip install --python .venv-labcad/bin/python "build123d==0.13.0" "matplotlib>=3.8"

build123d 0.13.0 requires Python >=3.11,<3.15 and pulls in the OpenCascade kernel through cadquery-ocp-novtk. The wheel is large; install once per project and reuse it.

All bundled scripts take --help. check.py standards runs without build123d installed.

Model files are executed, not parsed. gen.py, check.py, and snapshot.py import a *_model.py and call its build(), which runs arbitrary Python in the current environment. That is inherent to parametric CAD — the source is the design. Only run model files authored in this session or supplied by the user from a trusted location. If a model came from the internet, a shared drive, or an untrusted colleague, read it before running it and say that you did.

Required workflow

Follow these steps in order. Steps 5 and 6 are not optional, and step 6 is not waived by step 5 passing.

1. Route to a device family

Read the request, classify it, and load exactly one family reference. Do not load all four — they are long, and mixing conventions between families is a common source of error.

If the part genuinely spans two families — a microfluidic chip that bolts to an optical table — load the family that owns the critical interface, then read only the interface section of the second. State in your response which family you routed to.

2. Establish the interface dimensions before any geometry

Every part has at least one mating interface. Before writing code, write down for each interface:

• the source of the dimension: a published standard, a vendor drawing, or a user measurement;
• the nominal value and tolerance;
• the clearance or interference you intend, and why.

Look the number up in assets/standards.json or the family reference. Never write an interface dimension from memory. If the number is not in the standards file or the reference, ask the user for the vendor drawing or the measurement rather than guessing. A guessed interface dimension is the single most expensive failure mode in this skill.

A pocket receiving an external component is sized against that component's maximum material envelope — nominal plus its plus-tolerance — and only then given clearance. A shaft entering a hole instead uses the hole's minimum diameter; envelope does not model that case.

python scripts/check.py standards --list
python scripts/check.py standards --show slas-microplate-footprint

The bundled standard IDs (exact strings; do not guess variants): slas-microplate-footprint, slas-microplate-height, slas-microplate-flange, slas-well-positions-96, slas-well-positions-384, slas-well-positions-1536, cuvette-standard-10mm,

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