STL originally stands for stereolithography, one of the first 3D printing processes. The format only describes the surface of an object. That surface is broken down into lots of small triangles, like a mesh. For each triangle, the file stores its three corner points and the direction it faces outwards. The finer the mesh, the rounder curves look, but the bigger the file gets too.
Almost every CAD program can export STL, and common printer software can read it. That's why STL is something like the shared language of 3D printing. Before printing, a program called a slicer reads the file. It cuts the model into layers and calculates the paths the printer will follow.
The format does have its limits, though. An STL file has no unit of measurement, no colour and no material. You have to know whether a number means millimetres or inches. If it's read wrong, the part is suddenly 25.4 times too big or too small. The newer 3MF format, on the other hand, also stores units, colours, materials and print settings.
For a business that wants a part printed, a clean file saves time and money. The less that needs fixing, the sooner the quote is ready. Here's what to look out for:
- Closed model: the mesh mustn't have any holes. The experts call this being ‘watertight’.
- Correct dimensions: say whether the model was built in millimetres.
- Suitable resolution: too coarse gives angular curves, too fine gives huge files with no visible benefit.
- Wall thickness: very thin walls can't be printed sturdily with FDM.
We accept STL and 3MF files, and if you don't have one, we model your part from a sketch, photo or measurements.
A bike shop in Emmen needs a tool holder for its workbench that you can't buy anywhere. The owner draws it in a free CAD program and exports it as STL. In the slicer, the holder is suddenly just under 4 mm long instead of 10 cm. The program used inches for the export, and the STL file itself has no unit. After scaling by a factor of 25.4, the size is right. Exported as 3MF, the unit would have been saved along with it.