STL preparation checklist

An STL describes a surface as a set of triangles. For printing, that surface needs to fully enclose a solid volume.

Before export - Make sure the model is a solid body, not a set of surfaces - Remove construction geometry, hidden bodies and reference objects - Combine bodies that should print as one part; keep separate parts separate - Check minimum wall thickness against what you need (see our tolerances guide)

Export settings - Use a resolution fine enough that curves don't look faceted, but not so fine that the file becomes huge. Many CAD tools offer "fine" or deviation/angle settings; a chordal deviation around a few hundredths of a millimetre is a common starting point for small parts - Choose binary STL when available — it's much smaller than ASCII for the same geometry - Confirm the export units

After export - Open the file in a viewer (our upload page works) and check the dimensions - Look for warnings about open edges or non-manifold edges - Check the model isn't inside-out (inverted normals); most slicers can fix this, but it can indicate export issues

Watertight vs. non-manifold A watertight mesh has no gaps: every edge is shared by exactly two triangles. A non-manifold edge is shared by three or more, which often happens when bodies touch at an edge or overlap. Both problems can make volume and mass estimates unreliable and may cause slicing errors.