DWG to STL: convert an AutoCAD drawing for 3D printing

DWG to STL works in one step when the DWG contains 3D solids (AutoCAD's STLOUT command does it), and takes some modeling first when the DWG is a flat 2D drawing, which most are. This viewer cannot produce STL files; it shows 2D DWG and DXF drawings in the browser. Below: how to tell which kind of DWG you have, the AutoCAD and free FreeCAD routes, and what to check in the STL.

Does your DWG contain 3D solids?

STL describes a closed surface made of triangles. A slicer needs that surface to enclose a volume, so the DWG must contain 3D solids or watertight meshes. Lines, polylines, and circles have no volume, and a floor plan, a laser-cut part, or a logo in a DWG is just that: flat geometry on the XY plane.

Quick checks in AutoCAD: switch to a SW Isometric view and the Conceptual visual style, and see whether anything has thickness; or select an object and type LIST, which reports 3D SOLID or MESH for printable objects and LWPOLYLINE or LINE for flat ones. Without AutoCAD, open the DWG on dwgviewer.app: it renders 2D drawings, so a file that shows a plan with dimensions and a title block is 2D and needs modeling before it can become an STL.

Which method for which case

Online "DWG to STL converter" sites can only succeed on the first row; a 2D DWG comes back empty or as a zero-thickness shell.

How to convert DWG to STL in AutoCAD with STLOUT

1. Open the DWG and check units with UNITS. STL has no units, so slicers assume millimeters; if the model is in inches, scale it by 25.4 or set the unit in the slicer on import.
2. Make sure every object to print is a 3D solid or a watertight mesh. Join touching solids with UNION so the STL is one shell.
3. In older AutoCAD releases STLOUT required the model to sit in the positive XYZ octant; if the command complains, MOVE the model so all coordinates are positive.
4. Type STLOUT, select the solids, press Enter, and answer Yes to a binary STL (smaller, universally readable). Alternatively, EXPORT and choose "Lithography (*.stl)".
5. Set FACETRES to a higher value (up to 10) before exporting if curved surfaces look faceted in the slicer; this controls how finely arcs are tessellated.

AutoCAD LT cannot create solids or export STL. BricsCAD runs the same commands; see also the reverse direction on STL to DWG.

From a 2D DWG to STL with FreeCAD (free)

Most "convert DWG file to STL" requests start from a flat drawing, so the real job is giving it thickness. FreeCAD handles both the import and the modeling. Install FreeCAD and ODA File Converter, set the ODA path in Preferences > Import-Export > DWG, then File > Open the DWG (or convert to DXF first via DWG to DXF and open the DXF, which needs no helper).

In the Draft workbench, select the imported polylines that form a closed outline and use Draft > Upgrade until they become a Face. Switch to the Part workbench, select the face, and use Part > Extrude with the thickness you want; subtract holes with Part > Cut. For a plan, extrude wall outlines to wall height and openings as separate cuts. Finally select the solid and File > Export as STL Mesh (.stl); FreeCAD asks for a surface deviation, where 0.05 mm is a good value for printing.

Fusion 360 and Onshape do the same with sketch import and extrude. Tinkercad imports SVG rather than DWG, so for that route export the DWG as SVG first, which is something the viewer does (see DWG to SVG), then extrude in Tinkercad.

What to check in the STL

• Watertight. Open the STL in your slicer or in Windows 3D Viewer; any "non-manifold" or "open edges" warning means the solid was not closed. Fix in the CAD program or let the slicer repair it.
• Size. A 100 mm part arriving at 3.94 mm means inches were read as millimeters. Scale by 25.4.
• Orientation. The model should sit flat on Z=0 with the largest face down; rotate in the slicer if not.
• Facets. Visible flat faces on cylinders mean FACETRES or the export deviation was too coarse.
• One shell. Several separate solids print as separate parts; union them if they should be one.

STL is a 3D format, so this viewer cannot show it; what it can do is confirm what the source DWG contained before you start. How to open a DWG file explains the viewer's limits.

Frequently asked questions