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A model that is larger than the build volume of your printer has to be printed in parts. To cut it into parts, use the Section tool: it cuts the selected objects with a plane, can close each cut with new triangles, and keeps both halves as separate objects.
In 3D printing, slicing usually means making layers and G-code in a slicer. This article is about the other meaning: cutting a model into pieces that fit the printer.
Open the Section tool
- Open the model and select it in the Scene tree.
- Click Mesh Edit › Section. The same tool is also on the Inspect tab.
The Section panel opens. Until you set a plane, it shows four buttons and the hint Clip object to get cross section.
Set the cutting plane
There are three ways to set the plane:
- Plane YZ, Plane XZ, Plane XY make a plane across the X, Y or Z axis. The new plane starts at the edge of the model, at its lowest coordinate along that axis.
- Import Plane takes the position of a plane object from the scene: click the button, then click the plane object in the viewport. To make such a plane from the selected objects, use Inspect › Plane.
- Drag with the left mouse button across the model in the viewport. The plane goes through the line you draw and is perpendicular to the screen.
When the plane is set, the panel shows its controls:
| Control | What it does |
|---|---|
| Normal | The direction of the plane, as X, Y and Z components |
| Shift | The position of the plane along its normal. Drag the value or type an exact number; the arrow buttons next to it move the plane in small steps |
| Flip | Turns the plane the other way |
| Show Plane | Shows or hides the plane in the viewport |
| Clip Objects | Hides the part of the objects on one side of the plane, so you see the cut face. On by default |
| Recolor Objects | Gives each object its own color in the scene |
The Section Window (open by default) shows the outline of the cut in a separate 2D window. Use it to check that the cut does not go through a thin wall or a small detail. To measure in it, hold Ctrl (Cmd on macOS) and click two points in the window. All controls of this window are described in the Section article of the Inspect section.
Cut the model
The cutting controls are in the Cut section at the bottom of the panel:
| Control | What it does | Default |
|---|---|---|
| Cut Objects | Cuts the selected objects by the current plane. Unavailable when no object is selected | — |
| Fill Section | Fills the cut of each object with new triangles, so every part stays closed | Off. Turn it on for 3D printing |
| Keep Both Sides | Makes two objects from each original object. When it is off, only one side remains | On |
After Cut Objects, the two parts get the name of the original object with _cutP and _cutN at the end. Clip Objects turns off, so you see the whole model again. The plane stays where it was, ready for the next cut.
Split a model that is too big for the printer
- Select the model and read its size in the Information panel. Switch the panel from LOCAL to WORLD and read World Box Size: it is the size you see in the scene, also after Scale or Transform Object (Local Box Size ignores them until you run Transform › Apply Transform). Compare it with the build volume of your printer.
- Open Mesh Edit › Section.
- Click the plane button across the longest side of the model. For example, if the model is longest along X, click Plane YZ.
- Move the plane with Shift to the place of the cut. Choose a place where the cut does not go through small details, and check the outline in the Section Window.
- Turn on Fill Section, keep Keep Both Sides on, and click Cut Objects.
- Both parts stay selected. To cut them again, move the plane to the next position and click Cut Objects: every selected part is cut. To cut only one part, select just that part in the Scene tree first.
- Repeat until every part fits the printer. For a cut across another axis, click another plane button.
After a plane button, Shift is the distance from the edge of the model. After each cut, Shift starts again from 0 at the current position of the plane. So to cut at equal intervals, type your step in Shift before each cut.
In the example in the screenshots, the housing is 311.6 mm long along X. One cut with Plane YZ and Shift at 155.8 mm gives two parts of about 156 mm each.
The Sections Step field in the Export section does not cut the model. With Number of Sections set to Many, it sets the distance between parallel outlines that Create Sections with Step adds to the scene as line objects.
Check the parts before printing
- Look at the parts one by one: press F4 to show only the next object in the Scene tree, and F3 to show only the previous one.
- Check that each part is closed and ready for printing with Mesh Repair › Mesh Healer. Fill Section closes the cut, but holes that the original model had stay open.
- Select each part and save it to its own file with Home › Export.
Connect the parts
To join the printed parts, add pins to one part and matching holes to the other. Make a pin with Mesh Edit › Create Simple Objects (for example, a cylinder) and put copies of it on the cut face with Mesh Edit › Place Mesh. The Place Mesh article shows how to unite the pins with one part and subtract them from the other.
A plane cut is not the only way to split a mesh. To cut along a curved line on the surface, use Mesh Cut & Measure. To separate a feature by a boundary through two points, use Segment Mesh.
