wormgear 0.1.1

Worm gears for build123d, with DIN-3975 engineering analysis

Wormgear

Worm gears for build123d, with real DIN-3975 engineering behind the geometry.

from wormgear import WormGear, WormWheel

worm  = WormGear(module=2.0, num_starts=1, length=40)   # is a build123d Part
wheel = WormWheel(module=2.0, num_teeth=30)             # is a build123d Part

worm.export_step("worm.step")
wheel.export_step("wheel.step")

Or for a guaranteed-matched pair in one line:

from wormgear import make_pair

worm, wheel = make_pair(module=2.0, ratio=30, length=40)

That's the whole API for most users. Both classes subclass build123d.BasePartObject, so you can show(), export_step(), or compose them into assemblies directly.

Why use this

Wormgear supplements the excellent build123d gear ecosystem (bd_warehouse for spur gears and other parts, py_gearworks for spur / helical / bevel / cycloid / inside-ring) with specialist support for worm gears, which neither of those libraries currently covers.

What it does:

• Implements real DIN-3975 derivation. Lead angle, pitch diameter, addendum/dedendum, throat radius for globoid worms — all standards-compliant rather than approximate.
• Calculates load-capacity-relevant fields per DIN-3996 (efficiency estimate, self-locking detection, recommended materials).
• Generates exact geometry. No "good enough after manufacturing" approximations — the STEP file is exactly what your CNC will cut or your printer will print.
• Two tooth profiles: ZA (straight flanks, CNC-friendly), ZK (slightly convex, 3D-print-friendly).

Install

pip install wormgear

Requires Python 3.12+. build123d (and its OpenCascade backend) installs automatically.

Beyond the basics

Engineering analysis

from wormgear import make_pair, check_mesh

worm, wheel = make_pair(module=2.0, ratio=30, length=40)

# Kinematic mesh validation (independent of how the gears were built)
report = check_mesh(worm._params, wheel._params, worm._assembly_params)
print(f"ok: {report.ok}, ratio: {report.ratio}, "
      f"centre distance: {report.centre_distance_mm:.2f} mm")

For full DIN-3975 design analysis (efficiency, self-locking, undercut, etc.):

from wormgear.calculator import design_from_module, validate_design

design = design_from_module(module=2.0, ratio=30)
result = validate_design(design)
print(f"efficiency: {design.assembly.efficiency_percent:.1f}%, "
      f"self-locking: {design.assembly.self_locking}")
for msg in result.warnings:
    print(f"warning: {msg.message}")

Features (bores, keyways, set screws)

from wormgear import WormGear
from wormgear.core import BoreFeature, KeywayFeature

worm = WormGear(
    module=2.0, num_starts=1, length=40,
    bore=BoreFeature(diameter=8.0),
    keyway=KeywayFeature(),  # auto-sized DIN-6885 keyway
)

Web calculator

Don't want to write any code? wormgear.studio is the browser-based version of the calculator. It produces a JSON file you can load:

from wormgear import WormGear, WormWheel
from wormgear.io import load_design_json

design = load_design_json("my-design.json")
worm  = WormGear.from_design(design, length=40)
wheel = WormWheel.from_design(design)

CLI

For shell-driven workflows (CAM pipelines, batch generation):

wormgear design.json -o out/
wormgear design.json --profile ZK --globoid --worm-bore 8

See wormgear --help for the full set of options. (wormgear-geometry is kept as a backwards-compatible alias.)

Advanced: virtual hobbing

For high-precision conjugate contact (e.g. high-load applications or contact-stress analysis), wormgear.advanced.virtual_hobbing kinematically simulates the hobbing manufacturing process — slower than throated=True, but produces sub-tenth-percent-accurate tooth flanks:

from wormgear import WormGear, WormWheel
from wormgear.advanced import virtual_hobbing

worm = WormGear(module=2.0, num_starts=1, length=40)
wheel = WormWheel(module=2.0, num_teeth=30)
precise_wheel = virtual_hobbing(worm, wheel, steps=72)

Most users want plain WormWheel(throated=True) — reach for this when you specifically need kinematic accuracy.

Related libraries

Wormgear is one library in the build123d gear ecosystem:

• bd_warehouse — spur gears, fasteners, bearings, threads, sprockets
• py_gearworks — spur, helical, bevel, cycloid, and inside-ring gears

Use them together: spur / helical gears from bd_warehouse or py_gearworks for parallel-shaft stages, wormgear for perpendicular reduction stages.

Documentation

• Architecture — system design
• Geometry — technical specification
• Engineering Context — DIN-3975/DIN-3996 background

Background

Created for custom worm gear design in luthier (violin making) applications, where standard gears don't fit unusual envelope constraints. Extended to support CNC machining and 3D printing for makers and engineers.

License

MIT

Author

Paul Fremantle (@pzfreo)