Cut an STL in half online, free

Five steps

1. Open the tool and drop your model in. STL, OBJ and FBX are read, and the file is opened by your own browser rather than sent anywhere.
2. Pick your printer, so its build volume is drawn under the model and you can see what has to fit.
3. Press Draw cut line and drag a line across the model where you want it split. The cutting plane follows the line you drew, at any angle.
4. The halves come apart with a tapered peg on one and its socket on the other. Move it, resize it, or swap it for magnet pockets on the paid plans.
5. Download the pieces: one STL each, in millimetres, ready to slice.

Pegs, so the halves line up

Two flat faces glued together slide while the glue sets, and a bust printed in two halves shows it at the neck. A peg keys them: the pieces seat in one position and one only. Split3D cuts the peg into one half and its socket into the other, with the clearance you choose, 0.2 mm by default, which most FDM printers hold. Magnet pockets instead, if the two halves should come apart again.

A hole in the mesh stops the cut

A model with holes, or with faces turned the wrong way, makes any boolean cut fail or come out inside-out. The tool counts those edges when the file opens and offers one button that welds the duplicate corners, closes the holes and turns every face outwards. Repair first, cut after.

Or do it in your slicer

Bambu Studio, OrcaSlicer and PrusaSlicer all have a cut tool with dowels built in. If the model is already loaded there and a straight plane cut is all you need, use it: it is the shortest path. Come here when you want no install at all, a seam that follows the shape rather than a flat plane, magnets rather than pegs, or a connector somewhere there is no cut.

Questions

Is my STL uploaded? No. The cut runs on your machine. The model is never sent anywhere, never cached, never seen by us.

Is it really free? Yes. The plane cut, the peg and the STL export cost nothing, and nothing is counted: export as many models as you like. Free files carry a small Split3D engraving and are for personal use.

How big can the model be? A couple of million triangles works on a normal laptop. Bigger sculpts take longer, because the whole job runs on your own processor, but there is no size cap on our side.