Convert IGES to STL

Why convert IGES to STL?

IGES is an older CAD exchange format that still turns up in files from legacy systems, aerospace and automotive suppliers, and some CAM and machining workflows. Like STEP it describes exact curves and surfaces, so a slicer cannot use it directly. IGES to STL tessellates those surfaces into triangles using OpenCascade in your browser, with draft, normal or fine quality to control smoothness. Unlike STEP solids, many IGES files contain only loose surfaces without a closed volume. That can leave gaps where surfaces fail to meet, which is the main reason an IGES conversion may not print cleanly. The units recorded in the IGES file are used, so the STL should have the right size in millimetres.

How to convert IGES to STL

1. Drop your IGES file onto the converter — it opens in your browser, nothing is uploaded.
2. Check the preview and the dimensions in mm; fix units or the up axis in “Units & orientation” if the size or orientation looks wrong.
3. Choose STL as the output (binary is smaller; ASCII is human-readable) and click Convert. Several files download as one ZIP.

What carries over from IGES to STL

What changes

• Exact surfaces become triangles; curves are approximated.
• Loose or untrimmed surfaces can leave gaps in the mesh.
• Layer, colour and entity metadata are not carried into STL.
• Assemblies are flattened into one mesh.

Tips

• After converting, check the watertight flag; if it says no, run the print check and repair.
• Try Fine quality if edges between surfaces do not meet cleanly.
• If the IGES came from a CAD system you can still access, exporting STEP solids will usually be cleaner.
• Verify the dimensions against the original drawing, as old files sometimes use inches.

About IGES files

IGES was first published in 1980 by the US National Bureau of Standards, with participation from Boeing, General Electric and others, as one of the earliest standards for moving CAD data between different systems. Files use the .igs or .iges extension and are fixed-width 80-column text records divided into Start, Global, Directory Entry, Parameter Data and Terminate sections, a layout that reflects its punched-card heritage. IGES describes wireframe curves, trimmed and untrimmed NURBS surfaces, and, in later revisions, solids, but in practice it is mostly used for surface data. The format has not been updated since version 5.3 in 1996; STEP replaced it as the preferred standard. Even so, aerospace, automotive and tooling companies keep large IGES archives, and some CAM and surface-modelling programs still ask for it.

About STL files

STL was created by 3D Systems in the late 1980s for its stereolithography machines, and it became the default exchange format for 3D printing. A file describes a surface as a list of triangles, each with three vertices and a facet normal. That is all it contains. There is no header field for units, no colour, no texture and no notion of separate parts. Two flavours exist: ASCII, which is readable text but large, and binary, which spends exactly 50 bytes per triangle after an 80-byte header and a 4-byte triangle count. Binary is what almost every modern tool writes. Because the format is so small and so old, every slicer, CAD package and mesh editor can read it, which is why hobbyists still download most printable models as STL from sites like Printables and Thingiverse.

3D printing notes

STL is still the safest file to hand to a slicer. Bambu Studio, PrusaSlicer, OrcaSlicer, Cura and the resin tools Chitubox and Lychee all import it, and they all treat the numbers as millimetres. The usual problems are scale (a model exported from a metre-based tool arrives 1000 times too small) and meshes that are not watertight, which makes slicers fill or skip regions. MeshShift shows the real dimensions before you convert and can scale from metres automatically. Its print check lists holes, non-manifold edges and flipped normals, and one click rebuilds a closed solid at the same size. If you need colours or several plates in one file, use 3MF instead.

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