Why split a 3D print into parts
The usual reason is size. A helmet or a long panel will not fit a 220 × 220 mm bed in one piece, and you find out when the slicer shows it hanging over the edge. Splitting also gives each half a flat face to print on, which can remove the need for supports under a dome or an overhang. A two-color model can be printed as two pieces on a single-nozzle printer and glued.
How to split an STL file in half
- Drop the model on the viewer.
- Open Section in the left toolbar, choose X, Y or Z and drag the slider to where the cut should be. Flip shows the other side.
- Press Edit, open Cut with a plane and press Cut into two parts.
- Press Save part 1 and Save part 2. Each one downloads as its own STL.
The section plane shows the cut before you make it
The cut uses the same plane as the section view. While you drag it, the inside of the part shows in red, so you see the wall thickness and any internal cavities right at the cut line. Move the plane until the cross-section is solid and wide enough to glue.
The plane runs along X, Y or Z. For an angled cut, turn the model first under Rotate, mirror, move by the angle you need, then cut. Rotate the halves back before printing if you want them in the original pose.
Where to put the cut
A good split line runs through a flat, thick area of the part. Keep it away from thin fins, small text and holes, which turn into fragile edges once the part is in two. On a figure, a natural line such as a belt, a collar or the base hides the glue seam.
Look at the area of the cross-section in red: a wider face gives the glue more to hold. Cut so that each half has a flat face that can sit on the bed without supports.
Capped halves from the STL splitter
The cut is capped: the open face of each half is filled, and each part is a closed solid that a slicer reads without complaint. The cutting engine is manifold-3d, and it needs a watertight model to start with. If the mesh check reports holes, the tool asks for Repair first; STL repair covers what that does.
More pieces, joints and putting it back together
One cut gives two parts. For three or more, save a part, open it again and cut once more. To add a joint, add a peg-shaped file in Combine & booleans and subtract it with A − B to leave a socket, then print a matching pin.
The STL editor can also join pieces back: A ∪ B merges two bodies into one. Check each half's size and weight on the measure page, or save it as 3MF through STL to 3MF.
Questions and answers
Do I get one file or two after splitting?
Two. Save part 1 and Save part 2 download each half as its own STL.
Are the two halves watertight?
Yes, if the model was watertight before the cut. The cut face is capped on both parts.
Can I cut an STL along a diagonal?
The plane follows X, Y or Z. Rotate the model by the angle you need first, then cut.
How do I split an STL into several parts?
Cut once, save the parts, open one of them and cut again. Repeat until each piece fits your bed.
My model is still too big for the bed after one cut. What now?
Cut each half again along another axis, or scale the part down first on the scale STL page.
Does cutting upload my model?
No. The cut runs in your browser tab and both parts are saved from there.