Watertight mesh
A closed 3D mesh with no holes, gaps or loose edges, so it encloses a solid volume.
Why it matters for production
3D printers, including resin printers used for casting, need watertight models, because the slicing software must know what is solid. Holes, gaps and overlapping surfaces lead to failed prints, missing walls or extra material.
Why it matters for renders
Renderers are more forgiving than printers, but open meshes still cause problems. A gap between two surfaces shows as a thin dark or bright line. A missing face lets you see through the metal into the inside of the shank. Inside faces that should not exist can catch light and create strange specks in close-ups.
Common causes
- surfaces that were never joined in CAD,
- boolean operations that partly failed,
- duplicate surfaces stacked in the same place,
- stones intersecting the metal instead of sitting in seats.
Checking and fixing
In Rhino, joining surfaces into closed polysurfaces and checking for naked edges catches most issues. Mesh tools in Blender, Netfabb and similar software can find holes and non-manifold edges and repair them. Repair before exporting, because a clean source file gives a clean mesh in every format.
For rendering only, small issues inside the piece that the camera never sees do not matter. Focus on the surfaces visible in your product angles.