Nearly every CAD program exports both formats. Which one you send us makes a bigger difference than most people think.

STL: The Standard Format With Weaknesses

STL (Standard Tessellation Language) describes a 3D surface as a mesh of triangles. The format has been established since the 1980s and is instantly readable by every slicer.

The problem: STL stores no dimensional information beyond millimeter coordinates. There are no curves, no dimensioning, no tolerance callouts – just triangles. Curved surfaces are approximated with many small triangles, which leads to faceted surfaces in the print at low resolution.

Also: editing an STL requires specialized mesh software. Simple dimension changes are often impossible without the original CAD file.

STEP: The Superior Format

STEP (Standard for the Exchange of Product model data, ISO 10303) stores the part as a parametric model with exact curves, surfaces and geometries.

The advantages for 3D printing:

Dimensional accuracy. Cylindrical surfaces remain true cylinders in the STEP format – they’re only resolved into triangles in the slicer at the point of export to machine code, and at a much higher resolution than an exported STL.

Editability. We can make simple corrections directly in the STEP model – adjusting a diameter, correcting a bore offset – without rebuilding the entire model.

Tolerance callouts. In the STEP format, we can identify critical dimensions directly in the model and account for them during slicing.

When Is STL Still Fine?

STL is sufficient when:

  • The part has no tight tolerances (decorative parts, prototypes without fits)
  • You just want a specific, unmodified part printed
  • The STL was exported at sufficiently high resolution (angular tolerance < 0.5°, edge length < 0.1 mm)

How to Export an STL Correctly

If you can’t provide a STEP file, pay attention to the following during STL export:

  1. Increase resolution – in SolidWorks/Fusion 360: set resolution to “Fine” or “Custom”
  2. Angular tolerance to 0.5° or less
  3. Maximum edge length to 0.1 mm or less
  4. Check units – STL has no unit; the default is millimeters, but parts exported in inches do occur

Our Recommendation

Send us the STEP file if you have it. It noticeably improves result quality for technical parts and gives us more flexibility during preparation.

Only have an STL? No problem – we can work with that. What matters is that the geometry is watertight (no open edges, no flipped normals). If you’re unsure, just upload the file and we’ll check it for free.