⚙ GearForge

Standards-correct involute gears, timing-belt pulleys and splines — exported as laser-ready, kerf-compensated SVG / DXF. Zero dependencies, runs in your browser.

Live app → https://1400130-collab.github.io/gearforge/

A generated involute gear pair (z20 : z40) meshing — real GearForge output

• External spur gears — ISO 21771 geometry, DIN 867 / ISO 53 basic rack (ha*=1.00, hf*=1.25, ρf*=0.38), pressure angles 14.5°/20°/25°, profile shift, circular-backlash allowance, true rack-generated trochoidal root fillets (undercut on low tooth counts is reproduced correctly, not approximated).
• Internal / ring gears — annulus with involute toothed bore, rim sizing, bolt circles.
• Racks — mm-true pitch, analytic corner fillets, mounting holes.
• Timing pulleys — GT2 (2/3/5 mm), HTD 3M/5M/8M, T2.5/T5/T10, AT5, MXL/40DP/XL/H. OD = z·p/π − 2·PLD with the industry-standard SDP/SI groove profiles; adjustable belt-fit clearance.
• Involute splines — ISO 4156 / ANSI B92.1, 30° pressure angle, flat and fillet root, external shaft + internal hub cross-sections, side-fit clearance.
• Bores & features — round, D-flat, hex, square, and round + DIN 6885 keyway (standard ×ばつh / t2 table), bolt-circle holes.

• SVG with real-millimetre width/height + matching viewBox (imports mm-true into LightBurn, Inkscape, xTool CS, Glowforge...). Layers: CUT (red) and ENGRAVE (blue, pitch circle + centermark + label).
• DXF R12 (POLYLINE/CIRCLE/TEXT, metric header, CUT/ENGRAVE layers) for CAM tools that prefer DXF.
• Kerf compensation: the beam path is offset by kerf/2 along the outward material normal — outer contours grow, holes shrink — so the finished part is dimensionally true.
• Dimension & inspection report (plain text): pitch/base/tip/root diameters, tooth thickness, span measurement Wk and measurement over pins M so you can verify a cut gear with calipers, plus pair data (working center distance, working pressure angle, transverse contact ratio εα).

node tests/run-tests.js runs 25 checks that compare generated point geometry against independent closed-form standards formulas, including:

• tooth thickness sampled from the generated flank vs. s = m(π/2 + 2x·tanα) − Δs (≤ 1 μm);
• a pin placed numerically against the generated flanks vs. the closed-form measurement-over-pins (≤ 5 μm) across a parameter sweep;
• span measurement vs. Wk = m·cosα(π(k−1⁄2) + z·invα) + 2x·m·sinα;
• working center distance / contact-ratio round-trips;
• a z20:z40 pair rolled through a full tooth pitch with point-in-polygon interference checking — zero interpenetration;
• undercut cases (z=8 and below) still produce simple, closed, laser-cuttable polygons;
• GT2 20T pulley outside diameter = 12.224 mm (commercial spec), groove counts, pitch consistency z·p = π·d for all 14 belt profiles;
• ISO 4156 major/minor diameters reproduced by the generated splines;
• kerf offsets verified radially and for self-intersection;
• DXF group-code structure and SVG mm-true headers.

The root fillet is generated exactly as a hob/rack cutter would: the rack tip corner (radius ρ) is rolled over the pitch circle, its center tracing C(φ) = R(φ)·(ξc + rp·φ, rp + ηc). By the fundamental law of gearing the contact normal passes through the instantaneous pitch point I(φ), so the cut surface is P(φ) = C(φ) + ρ·unit(C(φ) − I(φ)) — the true trochoid envelope. The tooth boundary at each radius is then the minimum half-angle over all cutter elements (corner envelope, folded across the space centerline for the adjacent corner, plus the involute which is only valid above the form radius r_Ff = √(rb2 + (rp·sinα − h_fEff/sinα)2)). This handles tangent joins, undercut loops and cross-centerline cuts in one uniform construction — no special cases.

• Online: https://1400130-collab.github.io/gearforge/
• Locally: clone and open index.html — it works from file://, no build, no server, no dependencies. (Optional: python3 -m http.server if you prefer.)
• Tests: node tests/run-tests.js (Node ≥ 18, uses node:test).

index.html / style.css UI shell
src/geometry.js vectors, arcs, RDP, kerf offset, bores/keyways
src/involute.js spur/internal/rack generation + mesh & inspection math
src/pulley.js 14 belt profiles + pulley generation
src/spline.js ISO 4156 splines (shaft + hub)
src/exporters.js SVG + DXF R12 writers, report
src/app.js UI: forms, live preview, mesh animation, exports
tests/run-tests.js geometry-vs-formula test suite
PLAN.md design document

• Measure your kerf on scrap (cut a 10 mm square, measure, kerf = 10 − measured). Typical: ~0.1–0.2 mm for 3 mm plywood/acrylic on a diode/CO2 laser.
• Acetal (Delrin/POM) and acrylic make good gears; plywood works for prototypes.
• Small modules (< 1 mm) approach kerf scale — expect reduced accuracy; the app warns when kerf/2 is large relative to the root fillet radius.
• Gears run best with a small backlash allowance (default 0.05 mm) plus whatever your kerf calibration error leaves.

Geometry follows ISO 21771 / DIN 867 / ISO 53 (spur gearing), ISO 4156 / ANSI B92.1 (involute splines), DIN 6885 (keyways). Timing-belt groove outlines and pitch-line differentials are dimensional data from published SDP/SI belt specifications, as popularized by droftarts' parametric pulley (Thingiverse thing:16627) and proven by years of community use.

MIT — see LICENSE. Contributions welcome; every geometry change must keep node tests/run-tests.js green.