One model in, its parts out.
A figure's head, body, arms and legs meet at inward creases. The tool follows those creases to split the model into parts — to give each part its own filament colour, or to print them apart, with fewer supports, and put them back together.
How it works
Along the creases, not edge by edge.
Every edge between two triangles is scored by how sharply the surface folds there, measured on blurred normals so a rough surface does not shatter, and only an inward fold counts: the groove between a head and a neck is a border, the ridge of a nose is not. Regions are then merged, cheapest first, by the mean score along their whole shared border — a border survives only when it is concave all along, so one noisy edge cannot cut a part in two.
The whole merge order is recorded once, so moving the split level or the part limit is only a replay — milliseconds, even for a half-million-triangle file. Everything runs in a background thread of your browser; the file never leaves your computer.
To print apart, each part is a patch of surface, open where it was cut. The opening is capped by /tools/mesh-fix's repair — the rim traced, then the least-area surface stretched across it — and manifold-3d checks it is a closed solid. Before export, the triangles a border runs across are cut along it. The border comes from each part's share at every vertex, smoothed with its neighbours, so it is one clean line instead of the triangles' staircase; where a border already runs along a sharp edge of the model it stays there.
Painted 3MF or arranged 3MF?
Painted, when you print the whole model in one go on a multi-colour machine (AMS, MMU, toolchanger): the surface stays whole, with no seams. Arranged, when you print the parts apart — a single-colour printer prints each part in its own filament, big parts lie down for fewer supports, then you glue or fit them back.
It splits into too many crumbs — what now?
Move “How finely to split” left or set “Most parts”. For a sculpt or a scan with a rough surface, raise “Surface noise filter” under Advanced. For the few crumbs left, press “Clean up crumbs”, or pick them and press ⌫ to merge them into their neighbour.
Parts sit off their plate when the file opens?
The plates are laid out for the bed chosen here. If the printer selected in your slicer has a different bed, parts can sit off their plate: press Arrange there, and each part keeps its filament. Pick your own printer's bed for the closest layout.
Can I use a STEP or Fusion file?
Not yet: the tool works on triangle meshes. Export the model as STL, 3MF or OBJ from your CAD program first. The finer the mesh, the closer the split follows the groove.