How to open and view a STEP file
STEP is the format in which 3D models change hands between companies. Whoever receives one usually just wants to check whether the part fits - and does not need a CAD system costing thousands.
What is a STEP file?
STEP is an international standard, written down as ISO 10303. The file extension is .step or .stp - both are the same thing.
Unlike a mesh format such as STL, a STEP file holds the real geometry: surfaces, cylinders, radii, each described mathematically. That is why a hole stays a hole instead of becoming a polygon made of triangles. A STEP model can be edited further in a CAD program; an STL barely can.
A STEP file can also contain a whole assembly, meaning several parts with their positions relative to each other. When viewing it you then get a parts list instead of a single lump.
Which programs open a STEP file?
- Cubory - displays STEP through OpenCascade, the same geometry core commercial CAD programs use. Runs offline, costs nothing to view.
- FreeCAD - free CAD system, can also edit STEP. Powerful, but takes a while to learn.
- Your CAD vendor’s own viewer - from SolidWorks or Fusion, for example. Usually free, but tied to an account.
- Online viewers - handy when the model is not confidential. For customer parts, think twice before uploading.
Viewing a STEP file with Cubory
- Download Cubory, install it, drag the file in.
- On first opening, the geometry is meshed. For large assemblies that takes a few seconds - the file contains surfaces, not ready-made triangles.
- The parts list appears on the left. Clicking a part highlights it and pushes the rest back; the dot next to it hides the part entirely.
- Use Iso, Top, Front and Right for the usual views, Edges traces the outlines.
Why are all parts called "Part 1"?
That comes from the file, not from the viewer. Many CAD programs do not write meaningful names into the STEP file on export but use the same placeholder for every part. Cubory numbers such duplicates so the parts can at least be told apart.
If you need the names, ask the sender whether they can include part designations on export. In most CAD systems that is a setting in the export dialog.
STEP or STL - which one?
For manufacturing, for edits and for anything that needs dimensional accuracy: STEP. The geometry is described exactly.
For 3D printing: STL or 3MF. The printer needs a triangle mesh anyway, and these formats are exactly that. The other way round, turning an STL back into a clean CAD model is hard.
Cubory displays both, plus IGES, BREP, OBJ, 3MF, PLY and GLTF.
What does it cost?
Viewing, rotating, isolating parts and toggling layers: free, with no time limit and no account. Measuring, section views, exploded views and export belong to Pro: 9 € per month, 79 € per year or 199 € once, all net.
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