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How to Design STL Files for 3D Printing in Your CAD Program

Try these tips to optimize your design for STL—the common CAD format used in additive manufacturing


We know you have a range of CAD programs and file format options to choose from when designing and sharing your part designs. The STL file, short for stereolithography, is the primary CAD file format that’s used for additive manufacturing (3D printing) design projects. This tip covers how to effectively design 3D-printed parts for STL.

What is an STL File?

Originally created and developed by 3D Systems and now supported by many other software options, STL is considered the preferred and standard file type to use for 3D printing. STL files describe the surface of the part by breaking it into a collection of triangles. The STL file lists the location of each point of every triangle as well as which side of the triangle faces outwards. Compared to other CAD file formats, STL files have relatively little information.

Tesselation and Resolution in STL Files

Tessellation is the process of dividing the surface of the part into triangles. If the STL uses too few triangles, curved surfaces will be faceted. These facets will show up on the printed part, so it’s important to make sure the STL has the correct resolution.

That said, more triangles aren’t always better. Parts that consist only of flat surfaces don’t require as many triangles, and using high resolution settings can increase the file size exponentially, without yielding a better part.

Deviation Tolerances and Angle Tolerances in STL Files

Deviation tolerance is the export setting that determines how far away the surface of the STL can be from the surface of the native CAD file. The lower the deviation value, the closer the STL file resembles the native CAD model.

Angle tolerances is the export setting that refers to the direction a triangle faces compared to the triangles around it. The smaller the angle value, the smoother the transition between triangles. This setting is key for having the right resolution on fine features. As the angle tolerance gets smaller, file size increases significantly.

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