@rulecad/printcheck

Is this mesh printable on an FDM printer? Hand it triangles and your printer's limits; get back findings in plain words. No dependencies; browsers and Node 20+.

import { check } from '@rulecad/printcheck';

const printer = { bed: 256, overhang: 45, layer: 0.2, support_gap: 0.2, bridge: 5 };
const findings = check(triangles, printer);
// [{ level: 'pass', text: '20 × 4 × 12 mm, fits the bed' },
//  { level: 'warn', text: 'an underside at z 10 starts in mid-air: needs support …' }, …]

triangles is [[[x, y, z], [x, y, z], [x, y, z]], …] in millimetres, Z up, the bed at z = 0: the model is checked as it will print, so its orientation is part of the design. Any CAD library's output works once triangulated.

What it checks:

• Fits the bed (bed, mm) and sits on it: lowest point at z = 0, with faces flat on the bed.
• Overhangs steeper than overhang degrees from vertical.
• Flat undersides above the bed: each must start on something. Either it rests on a built-in breakaway support (one support_gap below a surface), or it bridges no wider than bridge mm. The bridge is the widest circle that fits in the underside, measured to the edges held up by material below. An underside held by nothing starts in mid-air.
• Closed solid: every edge is matched by a face on the other side. T-junctions count as closed, and so do hairline seams narrower than HAIRLINE (0.01 mm), which booleans leave and no printer can resolve. Wider gaps are holes.
• One piece: a loose piece would print as a stray bit or fall over. A cavity inside a part (its surface faces in) isn't a piece.
• Nothing starting in mid-air: the lowest point of a tip hanging down (an icicle), with nothing below it to print on. Its faces point down, and for a millimetre above it the surface stays narrow. The face-by-face overhang check misses a tip like this, because each of its faces may slope at 45° or less. A shallow dip in a smoothed underside spreads wide, so it doesn't count.

Several parts printed together (a keycap with an inlaid legend in another colour): pass { parts: [{ triangles, role }] }. Then one part resting on another isn't an overhang, and each part must be closed on its own. A part with role: 'support' is printed and then removed.

Also exported: bounds(triangles) ({ lo, hi, size }), seams(triangles) ({ gaps, tjunctions, hairlines }), shape(triangles) ({ pieces, tips }) and widest(polys, held, under) (the bridge measurement).