negative-support — Negative-Space 3D Print Support Generator

Generates model-conforming support structures for 3D printing. Unlike slicer-generated tree or grid supports, these are negative-space supports — exact shapes created by subtracting the model from a surrounding block, producing solid mesh that conforms to the model's actual surface contours.

Available on npm and as a browser app at negative.support/generate.

Install

npm install -g negative-support

Or run directly with npx:

npx negative-support model.stl

Usage

negative-support model.step                # STEP with B-Rep overhang detection
negative-support model.stl                 # STL with triangle-normal overhang detection
negative-support model.obj -m 0.15 -a 40   # tighter margin + stricter angle
negative-support model.step --3mf          # 3MF with model + supports + slicer settings
negative-support model.stl -o out.stl      # custom output path
negative-support model.stl -q              # quiet mode for scripting

Options

| Flag | Default | Description | | ----------------------- | ---------------------- | -------------------------------- | | -o, --output <path> | <input>_supports.stl | Output path | | -m, --margin <mm> | 0.2 | Gap between supports and model | | -a, --angle <degrees> | 45 | Overhang angle threshold | | --min-volume <mm³> | 1.0 | Discard pieces smaller than this | | --3mf | | Export 3MF with model + supports | | -q, --quiet | | Suppress progress display | | --version | | Show version | | --status | | Show license status | | --activate <token> | | Activate license token |

How It Works

1. Overhang Detection

Both STEP and mesh files produce targeted per-region supports through overhang detection:

• STEP files (.step/.stp) — B-Rep face topology provides exact face boundaries and normals via occt-import-js. Each face with a downward normal steeper than the angle threshold becomes a support region.
• Mesh files (.stl/.obj) — Triangle normals are computed per-face, then adjacent overhang triangles are clustered via BFS flood fill over shared edges. Each cluster becomes a support region, producing results comparable to STEP.

2. Support Generation

For each overhang region:

1. Bounding box column — A vertical column is extracted from the region's AABB, extending down to the build plate
2. Negative space — The inflated model (offset outward by margin along vertex normals) is subtracted from the column using boolean operations (manifold-3d)
3. Decomposition — The resulting shape is split into separate pieces
4. Filtering — Pieces smaller than minVolume or not touching the build plate are discarded
5. Merge — Overlapping pieces from adjacent regions are merged via geometric intersection testing

3. Output

• STL (default) — All support pieces merged into a single binary STL
• 3MF (--3mf) — Model + individual support pieces as separate objects with per-piece slicer settings (1 wall, 10% cubic infill)

API

Call activate() with your license token before generating. The token is the same one you use for the CLI.

import { generateSupports, activate } from 'negative-support'
import { readFileSync, writeFileSync } from 'fs'

await activate('ns_live_...')

const buffer = readFileSync('model.stl').buffer
const result = await generateSupports(buffer, {
  format: 'stl',
  margin: 0.2,
  angle: 45,
})

writeFileSync('supports.stl', Buffer.from(result.stl))
console.log(result.stats) // { pieces, faces, volume }

generateSupports() will throw if called without activation or if the free tier is exhausted. result.supportPieces contains individual ParsedMesh objects for custom export or 3MF packaging.

Documentation

Full docs at negative.support/docs.

Development

git clone --recurse-submodules https://github.com/drcmda/negative-support
npm install
npm run dev               # Frontend dev server on :5173
npm run dev:server        # API dev server on :8787
npm test                  # Full test suite
npm run build             # Build frontend
npm run deploy            # Build frontend + deploy to Cloudflare

License

See negative.support for licensing details.