STEP file: what it is and how to get it printed

What is inside a STEP file

STEP comes from the international standard ISO 10303, and the file itself, with the extension .step or .stp, is described in its part 21. It is used by computer-aided design (CAD) programs such as Fusion, SolidWorks, Inventor or FreeCAD.

A STEP file contains no triangles, but real surfaces, curves and holes with exact dimensions. A cylinder in it really is a cylinder, not a polygon. The units are written into the file, so the model never uploads at the wrong scale. The Library of Congress also has a description of the format.

When to send STEP

STEP is a good choice for technical parts you drew yourself: brackets, housings, jigs or spare parts. There is nothing to export to another format, you just send what your CAD program saves.

For printing, every model ends up converted to a mesh of triangles. With STEP we do that when we prepare it for printing, so curves come out smooth. If you want a part in several colours, send a 3MF instead, because STEP does not carry colours for printing.

What to watch out for with STEP

• Send the one part or assembly you want printed. If the file holds a whole assembly of 20 parts, we will print all of them. Hide or delete the parts you do not want before exporting.
• Print accuracy is not CAD accuracy. The nozzle is 0.4 mm and the layer 0.2 mm. For holes and joints that have to fit together, leave some clearance, and read more in the tolerances entry.
• Size. One part can be at most 246 × 246 × 256 mm, and the file up to 50 MB.