Tutorials

How to convert IGS to AutoCAD? (Solved)

Many people need a clear, step-by-step guide to convert IGS / IGES files into formats usable in AutoCAD (DWG, DXF, SAT). This article gives practical, beginner-friendly workflows, alternative methods, common errors and fixes, and actionable tips so you can complete the conversion reliably.

Quick answer — short and practical

If you need to get an IGS (.igs / .iges) file into AutoCAD, the most reliable approaches are:

  • Use Autodesk Inventor or Fusion 360 to open the IGES and export to SAT (ACIS) or DWG/DXF; then open/import that file in AutoCAD.
  • Or use a free tool like FreeCAD or Rhino to open the IGES and export to STEP, SAT, DWG, or DXF.
  • If your AutoCAD version directly supports IGES import, use the IMPORT command and choose IGES.

Choose SAT (ACIS) or STEP when you need solids with high fidelity; choose DWG/DXF when the IGES contains 2D geometry or you need native AutoCAD entities.

Why convert IGES to AutoCAD formats?

  • IGES is a neutral CAD format commonly used for surfaces and solids exchange, but not all CAD apps (or all AutoCAD versions) handle IGES natively.
  • Converting to DWG/DXF or SAT preserves editable geometry inside AutoCAD and avoids rebuilding models from scratch.
  • Choosing the right target format (SAT, STEP, DWG) affects whether you keep solids, parametric data, layers, and surface quality.

Preparation — what to check before converting

  • Check file extension: .igs or .iges.
  • Ask the supplier if they can provide STEP (.step/.stp) or SAT (.sat) — those are often easier to import.
  • Note expected geometry type: 2D curves, surfaces, or solid bodies.
  • Record the units used in the source file (mm, inch, etc.). Units mismatches are a common cause of scale problems.
  • Make a backup copy of the IGES file before trying conversions.

Method A — If AutoCAD supports IGES (fastest)

  1. Open AutoCAD (full version, not AutoCAD LT — LT may not support 3D import).
  2. Type the IMPORT command (or go to Application menu > Import).
  3. In the file dialog, set file type to IGES (.igs;.iges) and open the file.
  4. During import, choose correct units and any import tolerance options offered.
  5. Inspect the model: check solids/surfaces, layer mapping, and scale. Use 3D orbit and layer visibility.
  6. If the geometry came in as surfaces, attempt to stitch or convert to solids in AutoCAD (use the SOLIDEDIT or SURFSCULPT/STITCH workflows if available).

When this works, it’s the simplest path. If import fails or geometry is broken, use one of the external-conversion methods below.

Method B — Using Autodesk Inventor (recommended for best fidelity)

  1. Open Autodesk Inventor (or Inventor Professional).
  2. File > Open > choose IGES (.igs/.iges). Set units and import options (healing, stitch surfaces).
  3. Use Inventor’s Repair or Stitch tools if surfaces remain open; create solids from sewn shells.
  4. Export the repaired solid as SAT (.sat) or STEP (.step/.stp), or save a DWG if you need 2D drawings.
  5. In AutoCAD, use IMPORT or OPEN to bring in the SAT/DWG/STEP file. AutoCAD imports SAT natively as ACIS solids.

Why Inventor: it has robust surface healing and conversion tools that fix common IGES issues before export.

Method C — Using Fusion 360 (free for hobbyists/startups)

  1. Upload the IGES to Fusion 360 (Data Panel > Upload).
  2. Open the imported file in the Model workspace. Fusion will attempt to convert surfaces to B-Rep.
  3. If necessary, use repair and stitch tools to form solids.
  4. Export as SAT or STEP, or create a 2D drawing and export as DWG.
  5. Open the exported file in AutoCAD.

Fusion 360 is a good free/low-cost option with modern import/export tools.

Method D — FreeCAD (free, open-source)

  1. Install FreeCAD and open it. File > Open > select the IGES file.
  2. Switch to the Part or PartDesign workbench. Inspect the imported objects.
  3. Use repair / sewing / make solid tools to turn surfaces into solids (commands differ by FreeCAD version; look for “Create shape from faces”, “Refine shape”, or “Convert to solid”).
  4. Export the resulting solid or drawing as STEP (recommended) or DXF/DWG for 2D.
  5. Open the STEP/DWG in AutoCAD or import the STEP into a tool that can export SAT for best AutoCAD compatibility.

FreeCAD is powerful but may require more steps for surface repair.

Method E — Rhino or other commercial CAD tools

  • Rhino imports IGES very reliably and can export DWG or SAT.
  • Workflow: Rhino > File > Import IGES > Use Rhino’s Join/Cap/Repair tools > Export as DWG/SAT > Open in AutoCAD.

Rhino is especially good when IGES contains complex NURBS surfaces.

Method F — Online converters (fast, but caution)

  • Services such as AnyConv, GrabCAD Workbench, or dedicated IGES-to-DWG converters can convert files online.
  • Pros: fast, no local software required.
  • Cons: privacy concerns, file size limits, and less control over tolerance and repair options. Avoid confidential models.

Common problems and how to fix them

  • Scale or units wrong

    • Fix: Re-import selecting correct units, or scale the model in the receiving CAD by the known conversion factor (e.g., 25.4 for inch↔mm). Always check units during export/import.

  • Imported geometry is only surfaces, not solids

    • Fix: Use stitch / sew or heal tools in Inventor, Fusion 360, Rhino, or FreeCAD to convert surfaces into watertight solids; increase sewing tolerance if small gaps exist.

  • Missing faces, gaps, or bad topology

    • Fix: Run a geometry check / repair tool (many CAD apps have “repair”, “heal”, “check geometry” features). Manually patch holes if necessary. Export as STEP after repair for better downstream results.

  • Curves converted to many polylines (loss of smoothness)

    • Fix: Export using higher precision/tolerance settings (increase curve tolerance or reduce tessellation). Prefer export to SAT/STEP over tessellated formats (like STL).

  • Layers or attributes lost

    • Fix: Not all formats preserve layers. If preserving layer names is critical, request export as DWG/DXF from the original author or reassign layers after import.

  • AutoCAD can’t open STEP

    • Fix: Convert STEP to SAT (using Inventor, Fusion 360, or Rhino), or use plugins that add STEP support. Newer AutoCAD versions often support STEP better.

Practical tips for best results

  • Prefer STEP (.step/.stp) or SAT (.sat) as intermediate formats for solids — they preserve geometry better than IGES in many workflows.
  • When exporting from the source CAD, choose highest precision / smallest tolerance settings to reduce gaps.
  • Always check units at both export and import stages.
  • Consider asking the supplier for a native file or STEP/SAT instead of IGES.
  • Keep a copy of the original IGES and a log of conversion steps so you can reproduce or troubleshoot if needed.
  • For large/complex models, convert part-by-part rather than the entire assembly to isolate problem geometry.
  • Use a visual IGES viewer to confirm the IGES file is valid before attempting conversion (many free viewers exist).

Alternatives and when to use them

  • Use DWG/DXF if the IGES contains 2D drafting or profiles destined for AutoCAD drawings.
  • Use SAT if you need ACIS solids directly editable in AutoCAD.
  • Use STEP if you need to preserve high-fidelity solid geometry across different CAD systems.
  • Use STL only for visualization or 3D printing — it is a tessellated mesh, not editable CAD geometry.

FAQ — Can AutoCAD open .igs files directly?

Most full versions of AutoCAD have an IMPORT capability for IGES in some releases, but AutoCAD LT typically does not. If your AutoCAD version doesn’t support IGES, use Inventor, Fusion 360, FreeCAD, or Rhino to convert first.

FAQ — Which target format is best for importing into AutoCAD?

For editable solids, choose SAT (ACIS) or DWG for 2D. STEP is an excellent neutral option if you plan to re-export to SAT for AutoCAD.

FAQ — Will I lose layers and colors when converting?

Often yes — layers, metadata and colors may be lost or remapped during neutral-format conversions. If layers are critical, ask for a native DWG/DXF from the source CAD or map layers manually after import.

FAQ — Is there a free tool to convert IGES to a format AutoCAD accepts?

Yes. FreeCAD is free and can open IGES and export STEP/DXF; Fusion 360 has free tiers for hobbyists/startups. Both require some familiarity to repair geometry.

FAQ — The model imported but it’s all open surfaces — how do I turn it into a solid?

Use a CAD tool with stitch/repair capabilities (Inventor/Fusion 360/Rhino/FreeCAD). Increase sewing tolerance, stitch adjacent surfaces, then create solids from closed shells.

FAQ — Are online converters safe for confidential files?

No — avoid online converters for confidential or proprietary designs. Use local software with trusted environments instead.

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