What a cross-section shows inside a 3D model

A shaded 3D view shows only the outside of a model. A cross-section cuts it open along a plane so you can see what is inside: whether a part is solid or hollow, how thick its walls are, and whether there are surfaces inside that should not be there.

How a cross-section works

The viewer places a cutting plane along one axis, X, Y or Z, and hides everything on one side of it. Moving the plane sweeps through the model like a slicer moving through layers. Cutting along Z, from the bottom up, is the closest match to how a printer builds the part.

What to look for

• Hollow parts. Some models are exported as a thin shell. A cross-section shows a ring instead of a filled shape. That may be intended, as in a vase, or a mistake that leaves a part fragile.
• Internal walls. A leftover face inside a model, often from joining two shapes, shows up as a line across the cut. These often go with non-manifold edges. See what is a non-manifold edge.
• Overlapping shells. Two copies of the same part on top of each other show as doubled outlines.
• Wall thickness. You can see roughly how thick each wall is compared with the rest of the part, and find spots that are thinner than they look from the outside.
• Hidden cavities. Enclosed voids that will print as trapped empty space, or fill with support material that can never be removed.

Why it complements a printability check

A printability check counts faults in the mesh: open edges, flipped normals, non-manifold edges. A cross-section shows the shape of the solid. A model can pass the check and still be hollow when you expected it to be solid, or have a cavity you did not intend. Use both. See how to check an STL before you print it.

Reading the result

1. Start with a cut along Z in the middle of the part.
2. Move the plane slowly from bottom to top and watch for outlines that appear or vanish suddenly.
3. Repeat along X and Y for parts with detail on the sides.
4. If you find a problem, go back to the source model to fix it rather than patching the mesh.

On your phone

MeshView Pro cuts models along X, Y or Z so you can look inside a file you just received before you decide to print it.

A cross-section is not a slicer preview

A slicer preview shows the toolpaths: walls, infill and supports for your settings. A cross-section shows the geometry itself. Check the geometry first. If it is wrong, no slicer setting will fix it.