How to convert a STEP file to GLB

A STEP file is how engineers share a design. A web page cannot show one. GLB is the format it can show: a compact 3D file that browsers, AR viewers and most 3D programs open. This page takes you from one to the other with MeshOptimiser, on your own computer. Nothing is uploaded, and there is nothing to pay.

What you need

• MeshOptimiser, started once. See What you need and Start it the first time.
• Your model as a STEP file (.step or .stp). If it is still in your CAD program, see Native CAD files: export a STEP file first.

Steps

1. Start the app with start.bat (Windows) or start.command (macOS).
2. Drag the STEP file onto the window.
3. In the Import settings window, leave everything as it is and press Import. Standard under Surface quality is the recommended choice. See Open your first file.
4. Wait while the progress card works. A big assembly can take several minutes. A big file is meshed on several cores at once (up to eight processes); reading the STEP file itself uses one. Repeated parts are found and stored once, and the result is compressed. Open the same file again later, with the same settings, and it appears at once: the converted model is kept.
5. Look at the model. Properties on the right shows how heavy it is. Press Alt1 for the normal view.
6. Press CtrlE and choose GLB. In the Export window, the defaults for Unit scale and Up axis suit a GLB (see below).
7. Press Export GLB. The file arrives in your downloads folder.

Two settings that save a second try

Unit scale

CAD models are usually in millimetres, and glTF and most web viewers expect metres. The format’s own, the default, writes a GLB in metres, so the model should arrive at its real size. × 0.001 (mm → m) does the same by hand.

Up axis

CAD uses Z as up. glTF uses Y. The format’s own, the default, writes a GLB Y up, so the model should stand on its feet. Turn Z-up into Y-up (for glTF, OBJ, Maya) does the same by hand.

Leave Draco compression off unless the viewer you use can read it. See Which format should I choose.

Smoother curves, or fewer triangles

How round a hole looks, and how heavy the GLB is, is decided when the CAD surfaces are turned into triangles. That step is called tessellation. In the Import settings window, the named choices under Surface quality (Clean, Coarse, Standard, Fine and Ultra) set it for you. Open Tessellation under them to see the numbers, or to type your own.

Sag

How far a triangle may stand off the true surface, in millimetres. Smaller is smoother, with more triangles.

Angle

The most a curve may turn from one triangle to the next, in degrees. Smaller means rounder holes and fillets.

Min edge

The smallest triangle edge allowed. It keeps tiny fillets and threads from filling up with slivers. 0 is no limit.

Clean, Coarse, Standard, Fine, Ultra

Each sets a sag and an angle: 2 mm and 38°, 1 mm and 30°, 0.5 mm and 30°, 0.2 mm and 20°, 0.05 mm and 12°. Clean makes few triangles with fillets in even strips; small holes stay a little polygonal. The finer choices tighten the angle too, which is what rounds small holes.

Custom

Selected as soon as you type a sag or an angle of your own.

By part size

Small, medium and large parts each get a sag and an angle, so the housing comes in fine and the screws coarse. You set where small ends and large begins, as a share of the model’s size.

Even strips

Meshes curved faces along their own directions, so a fillet is a row of even strips, not a scatter of triangles. On by default.

Smooth shading

Writes the normals of the real CAD surfaces into the GLB. A fillet runs into the faces beside it without a visible seam, and sharp edges stay sharp. On by default.

Swap Y and Z

In the same window, under Clean-up. For a file that comes in lying on its side.

If the model is too heavy, try a coarser choice here before you reduce triangles afterwards. Fewer triangles at the source usually look better than a fine mesh that was thinned out.

How small will it be?

It depends on the model. The app’s README gives one example: a 320 MB STEP file became an 11 MB compressed GLB. Assemblies with many identical parts, such as bolts, shrink the most, because each shape is stored once. That is an example, not a promise for every file.

If the GLB is still too heavy, remove what nobody will see before you export. A sensible order to work in shows how, and Fit to budget takes a triangle count for the whole scene.

Without opening the viewer

To convert a file and do nothing else, drag it onto step2glb.bat (Windows) or step2glb.command (macOS). The GLB is written next to it. Or use the command line:

The command line is described in The command-line converter. Meshopt compression needs the free tool gltfpack on your PATH. If a viewer cannot open a Meshopt-compressed GLB, convert again with --no-meshopt, or export from the app instead.

Next

To see what the conversion did, read How to read the numbers. For the file formats in detail, see Export.