Know what to use next.
Start with one simple cut. You can isolate difficult areas, draw more detailed seams and adjust joints once the basic flow feels familiar.
- Open a model or try the demo egg. Check its size. If the app reports a problem with the solid, repair it before cutting.
- Choose Plane in Cut Tool. This is a simple way to try splitting the egg. Pick an axis and slide the plane to where you want the split.
- Choose your joints. For a plain split, use no built-in pins by setting Count to 0. Add joints when you want the pieces to locate together.
- Press Cut. Inspect both pieces. Use Back to editing if the cut needs moving.
- Export the parts. Choose the output you need. Save a project as well if you want to continue editing later.
Working Area is optional. You can cut the whole model directly. Opening this guide from the app leaves your work in its original tab.
Load, size & repair
Load and size
Open an STL or 3MF, or drop a supported model file into the viewport. Size X, Y and Z are in millimetres. Changing one dimension scales the others proportionally, so the model keeps its shape.
Reduce for cutting makes a lighter working copy for faster cuts and previews. Light preserves more detail; Strong removes more; Balanced sits between them. The original is retained for export. Use full detail discards the lighter copy.
Inspect & repair
| Action | What it does |
|---|---|
| Inspect | Checks the working piece for holes, flipped or duplicate faces and separate shells. |
| Repair — safe only | Cleans problems such as duplicate faces and faces inside out without deliberately changing the shape. It cannot close every hole. |
| Advanced — removes and adds faces | Attempts more substantial repairs, including holes and problematic joined surfaces. It can change the shape where it patches; inspect the result. |
| Separate the loose pieces | Makes separate objects from disconnected lumps in the current piece. |
Read the result of a repair: it may still report that the model is not a closed solid. A successful repair updates the working model; you should not need to export and reload it.
Start over returns to the loaded model or the latest repaired checkpoint, clearing paint, seams and cuts on the working piece. Finished parts already set aside remain. Start this seam again only resets the seam you are drawing.
Working area & paint
Use Working area → Paint when other parts of the model get in your way. Use Cut Tool → Paint to cut when you want to select an entire section to separate. Both entry points use the current paint selection; switching between them does not create another independent selection.
- Press Paint in Working Area, then paint the area you want to reach. Turn the model to paint its back too.
- Press Isolate the painted part. Everything outside that area is hidden from view and from brush hits. The cut still uses the whole model.
- Use Choose a cut tool to return to the tool chooser. Your paint is preserved. Use Clear paint if you want to start a fresh selection inside this area.
Show the whole model restores the hidden geometry and keeps your paint. Isolation changes visibility, not the model’s shape.
| Paint option | When to use it |
|---|---|
| Surface | Paints along connected faces and stops at sharp folds. Use it for following a surface without selecting every nearby layer. |
| Sphere | Paints faces within a 3D radius, including nearby disconnected layers such as clothing over a body. Hidden isolated faces remain untouched. |
| Paint size | Changes the brush radius. The displayed size is in millimetres. |
| Shift + paint | Removes faces from the selection. |
| Preview painted boundary | Shows the selection’s boundary without cutting. Orange means the preview is on. Click again to hide it; the button returns to grey. Undo also hides a visible preview before undoing paint. |
| Repair touching boundary | Appears when a boundary is found to touch itself. Adds a small amount of paint around the problem. It does not generally smooth a jagged outline. Undo restores the previous selection. |
| Clear paint | Removes the paint selection so you can begin again. |
Choose a cut tool
A seam is the line around the model where the pieces will separate. Pick the tool that makes that line easiest to place.
Line — a quick drawn cut
Draw across the model. The tool constructs a loop using the front and back intersections from your view. Useful for a quick cut, but turn the model and check the back: the inferred path can cross a different part than you intended.
Band — an adjustable loop
Draw a loop, then drag the orange line to reposition it. Click to pin a point; right-click a pin to release it. Smoothing controls how much a dragged stretch eases out afterwards; 0 leaves the drag as placed. Normal dragging follows the held surface. Alt-drag places a point on the visible surface beneath the pointer.
Rope — draw around the surface
Draw what you can see, release the mouse, turn the model, then continue from the loose end. Close the rope at its starting anchor. Use this when you want to control the path around the back instead of letting Line infer it. Drag handles to adjust the contour.
Paint to cut — select the whole section
Paint the entire region you want to separate, including its back. Preview the boundary, correct gaps or overspill, then press Cut. Painting a narrow stripe can produce two boundaries; paint the whole intended section for a cap-like split.
Plane — a straight cut
Pick X, Y, Z or View to orient the plane. Use Position and the handles to move it, and the tilt control to rotate it. If it crosses several separate areas, you can pick the crossing rings you intend to cut. Cut through everything returns to the full plane cut.
Multi-plane — specify the number of cuts
Enter the number of cuts across X, Y and Z. The planes start evenly spaced; click a plane to adjust it. Three cuts along one axis make four sections. Nothing is cut until you press Cut.
Auto multi-plane — fit your printer
Choose a printer preset or enter the build width, depth and height in millimetres. Keep clear at each edge reserves space around the bed and below the height limit. The proposed planes are editable; check the fit report after moving them. The cuts panel selects and positions individual planes.
Cut face & seam controls
| Option | What changes |
|---|---|
| Follows the seam | The separating surface follows the contour you drew. |
| Keeps the drawn step | Keeps a short level region around the seam to form a step rather than a thin edge. |
| Flat plane — replaces the seam | Uses a flat separating surface instead of keeping the drawn contour’s shape. |
| Start this seam again | Clears the seam in hand. Seams already put aside remain. |
| Keep this seam, draw another | When offered, puts a seam aside so multiple seams can be cut together. A kept seam can be brought back for editing. |
The app shows options relevant to the selected cut tool. A preview is a proposal; Cut performs the split.
Joints & fit
Joints help the printed pieces line up when assembled. Available controls depend on the cut and joint type.
Built-in pins — attached
A pin is part of one half and fits a socket in the other. Count sets how many to use; 0 gives a plain split. Pin thickness and length control its size. Clearance controls the gap around the pin.
Loose tenons — printed separately
Separate connectors fit sockets in both pieces. Per joint chooses the number of connectors; Auto uses the available face area. Size can be automatic or fixed. A round Shape allows rotation around a single connector; other shapes resist it. Fit changes the gap: increase it if the connector needs forcing, decrease it if it rattles.
Magnet sockets — removable assembly
Makes recesses for magnets. Choose a preset or enter the magnet’s measured diameter and thickness. Advanced fit provides extra room around the magnet and extra depth below the face. Check these against the actual magnets and your printing process.
Joint numbers
Number the joints engraves matching numbers on mating faces that received connectors. Depth controls the engraving depth. Useful when assembling many pieces.
Inspect joint positions after cutting. Where handles are offered, move pins along the cut face, adjust their length, or tilt the pins together. Reset the joints returns to the generated placement.
Review & continue
| Action | What it does |
|---|---|
| Separation | Spreads the pieces apart for inspection. It changes the view, not the exported geometry. |
| Close up / Explode | Switches between assembled and separated views. |
| Back to editing | Returns to the editable model with the seam retained so you can adjust and cut again. |
| Carry on cutting A / B | Makes that half the working piece and puts the other half aside as a finished part. |
| Keep both — done cutting | Keeps both halves as finished parts. |
Check the back of each piece and the joints before exporting. The object list lets you select parts; names and colours help distinguish them as the job grows.
Save & export
Projects preserve editable work. Give the project a name and save it in the browser, or use Save to a file for a project file you can keep elsewhere. Open a file in Projects restores that project. Exported STL files are geometry, not editable project backups.
| Export choice | Use it for |
|---|---|
| This model — STL | The current model as one STL. |
| Reduced working copy — STL | The lighter model, when a reduced copy exists. |
| Both halves / Part A / Part B | The result of the current cut, together in a 3MF or as individual STLs. |
| Every part — one 3MF | All the pieces collected in one file. |
| Every part + assembly guide — ZIP | A bundle of parts with assembly information. |
Export choices change with the current model and cut result. Choose the contents first, then export.
Sculpt, move & shapes
Sculpt — change the model surface
Smooth softens the surface, Inflate pushes it out and Flatten presses it toward a plane. Size controls the brush area; Strength controls how strongly it acts. Hold Shift to reverse the brush. Each stroke can be undone.
Mask paints areas to hold still during sculpting. Shift removes protection; Clear the mask releases all protected areas.
Move — position an object
Select an object, then use Move, Turn or Size to display its handles. Centre it on the model aligns its centre with the working model. Done — deselect removes the handles so you can draw again.
Shapes — add material or make a cutting object
Add a Cube, Ball, Tube, Cone or Ring, move it into place, then use Boolean. Choose Sharp, Chamfer (a bevel) or Round edges. Edge controls the size of the bevel or rounding. Where edge selection is offered, choose individual edges or use Back to every edge. Finish with Done with this shape.
Boolean — combine two solid objects
Select two objects. Union joins them. Difference removes object 2 from object 1. Intersect keeps their overlapping volume. Swap ① ② reverses their order; this matters for Difference. Both objects need to be suitable closed solids.
Mouse & keyboard
- Left-drag: use the active tool or its handles.
- Right-drag: rotate the view. Middle-drag: pan. Wheel: zoom.
- Shift + paint: deselect. During sculpting, Shift reverses the brush.
- Ctrl/Cmd + Z: undo. With a painted-boundary preview showing, the first undo hides that preview.
- Ctrl/Cmd + Shift + Z: redo. Redo can restore the selection rather than rerunning a cut; press Cut when ready.
- Axis widget: select a face to look from that direction.
- Panel edges: drag the divider to resize a sidebar. Open and close panel headings to keep the tools you need in view.
When something goes wrong
Cut asks me to repair the model again
Read the repair result in Inspect & repair. Safe repair may leave holes that require Advanced repair; even Advanced repair cannot fix every model. If it reports a cuttable model but the next cut repeats the same repair request, report the exact message and the steps that trigger it.
The boundary looks wrong or runs around twice
Rotate the model and inspect the whole selection. Unpainted gaps, islands or a painted stripe can produce multiple boundaries. Add paint or use Shift to remove overspill. The preview button only shows or hides a guide; it does not change the selected faces or cut the model.
I cannot draw on the model
Check the selected tool and finish moving any selected object or shape. If an area is hidden, Show the whole model brings it back. Try a fresh stroke directly on the surface and check the brush size.
The cut does not separate the model
Check that the seam fully surrounds the intended section, including its back. On layered models, isolate the relevant area and keep the seam on the intended surface. Read the cut’s error message before changing settings; use the offered details when reporting a repeatable failure.
Open the feedback forum to report an issue. Include the tool, exact message and sequence of actions.