Chris Collins

Tools · fabrication

STEP and IGES viewer

Open a STEP, IGES or BREP file in the browser — the assembly tree with each part's visibility and colour, measuring (distances, CAD edge lengths, hole diameters from round edges, face areas), a section plane, an exploded view, size, volume and mass — and export STL or GLB, or hand parts to the mesh tools.

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Works with

How to use it

When someone sends me a STEP file — a supplier’s part, a Fusion export from a friend, a bracket off a parts site — I want to look at it, check a hole size and get an STL out without opening a CAD program. This page does that. The file is read by OpenCascade, the same geometry kernel FreeCAD uses, running in your browser; nothing is uploaded.

It opens with a sample assembly (a base plate, two dowel pins and a cap plate, written as a real STEP file with planes and cylinders) so you can try the measuring before you load your own.

How to use it

  1. Open a file with Open STEP / IGES… or drop it on the view: .step / .stp (AP203, AP214, AP242), .iges / .igs, or OpenCascade .brep. The first file loads OpenCascade (about 7.6 MB, once; your browser caches it). Big assemblies take a while — the work happens off the page, so it stays usable. Coarse / Normal / Fine sets how finely curved faces are cut into triangles (0.2, 0.05 or 0.01 mm chord tolerance) for the view and for the exports.

  2. Parts lists the assembly as the file describes it. Untick a part or a sub-assembly to hide it, click the colour swatch to recolour it, click a name to select it. A selected part shows its size, position, volume, surface area, mass at the density you pick, how many CAD faces it has and the diameters of its round edges; Isolate shows it alone.

  3. Measure has four modes:

    • Select — click a part to select it.

    • Distance — click two points; a click near a corner snaps to it. You get the distance and ΔX, ΔY, ΔZ.

    • Edge — click one of the dark CAD edges. You get its length; for a round edge, the diameter, radius and centre (a hole’s rim gives the hole diameter), and for part of a circle its angle.

    • Face — click a face: its area, and for a flat face its normal. Each result has a Copy value button.

  4. Section cuts the model with a plane across X, Y or Z: drag the slider through it, Flip to look from the other side. Cut solids show red inside, and the cut outline is drawn with its length.

  5. Exploded view pushes the parts away from the middle of the model, for seeing how it goes together.

  6. Export the visible parts or the selected one as binary STL (one mesh), One STL a part, or GLB (glTF with the part names and colours, for Blender or a web page). Open in mesh repair, model splitter or mold maker hands the same mesh to those tools in a new tab. Exports use the parts where they belong in the assembly, not exploded.

Everything is in millimetres (STEP files carry their units; OpenCascade converts them). The view’s edges are the boundaries between CAD faces, so they match what you’d see in Fusion; volume and area are measured on the triangles, so a curved part reads very slightly small (less than 0.1 % at Normal).

Browser support

Any current browser with WebGL and WebAssembly: Chrome, Edge, Firefox and Safari, on desktop or phone. OpenCascade here is the single-threaded build, so it does not need the special server headers that threaded WebAssembly does. A large assembly needs memory: a phone may give up on files over a few tens of megabytes.

Privacy

Your file stays in your browser. The page downloads three libraries from jsDelivr the first time you use it: three.js (MIT) for the view, and occt-import-js 0.0.23 — OpenCascade compiled to WebAssembly, LGPL-2.1, loaded unmodified at run time and not part of this site’s code. Hand-overs to the other tools go through this browser’s storage (IndexedDB) and are deleted after two days.

Runs entirely in your browser — network requests go only to the services named on this page.