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An STL file describes a part as a mesh of triangles. It is quick to share and every CAD system can export it, but a careless export can lose the information needed to quote the part. These steps avoid the usual problems.
1. Export a closed solid
Export the solid body, not surfaces or an assembly of loose faces. A closed solid has no gaps, so its volume and mass can be measured. Our Check My Part tool tells you if the mesh has gaps.
2. Know your units
STL files do not store units. A part drawn in inches looks 25.4 times too small when read as millimetres. Export in millimetres if you can, and tell us the unit if you cannot.
3. Choose a sensible mesh resolution
A coarse mesh turns holes into polygons, and a very fine one makes huge files. A chord tolerance of about 0.01 to 0.05 mm and an angle tolerance of about 5 to 10 degrees suit most machined parts. Binary STL files are much smaller than ASCII ones.
4. Send a STEP file and a drawing too
An STL is an approximation. For machining we prefer a STEP file, which keeps exact circles and planes. A drawing tells us what the model cannot: tolerances, threads, surface finish, material and quantity.
5. Check it before you send it
- Size: does the bounding box match the part?
- Volume and mass: do they look right for the material?
- Closed solid: no gaps or overlapping edges
- Orientation: which face is the top, if it matters
