Exporting STL and 3MF#

Overview#

Almost every printer workflow passes through a mesh file. A mesh approximates the smooth surfaces of your Fusion solid with triangles. The two formats you will use most are STL (the long-standing standard: just triangles, no units, no colors) and 3MF (a modern container that stores triangles plus units, color or material assignment, multiple objects and often slicer settings). A third option, OBJ, is also offered; Autodesk describes it as unitless but able to reference color and texture. Autodesk also describes STL as unitless and 3MF as XML-based with units, colors and textures. For archival and for vendors who re-tessellate, STEP (a true B-rep format) is better than any mesh.

The two key decisions when exporting are the format and the mesh quality (refinement). Get those right and most "my print is faceted" or "my part is the wrong size" problems disappear. The dialog descriptions below follow Autodesk's help; numeric defaults for the Refinement levels are not given there.

Where to find it#

Step by step#

Exporting a single body#

1. Make sure the body you want is visible (general guidance: hidden bodies are often skipped).
2. In the Browser, right-click the body and choose Save As Mesh, or use Utilities > Make > 3D Print with Preparation Type Export.
3. Choose the format: 3MF, STL (Binary), STL (ASCII) or OBJ.
4. Choose the unit type (Save As Mesh offers Centimeter, Millimeter, Meter, Inch and Foot; millimeters suit nearly all printers).
5. In the 3D Print dialog, expand Refinement Settings and choose the refinement level; as general guidance use a finer level for curved or fine parts. Save As Mesh has no refinement controls in Autodesk's description.
6. Optionally adjust the individual surface deviation, normal deviation, maximum edge length and aspect ratio (explained below).
7. Choose a file name and location. Use a descriptive name with version, for example bracket_v4.3mf.
8. Click Save/OK, and open the file in your slicer. Check size, orientation and surface smoothness.

Exporting multiple bodies#

1. Select the bodies in the Browser (Ctrl+click) or select a component containing them.
2. Export as 3MF if you want each to be a separate object in the slicer; many slicers keep them separate with their relative positions (general guidance).
3. With Save As Mesh on a component, set Structure to One File (all bodies in one file) or One Body Per File. Some slicers merge overlapping meshes.
4. If bodies overlap in the design, decide: combine them into one solid (Modify > Combine, Join), or keep them separate. Overlapping bodies exported as separate shells can produce odd slicer results.

Exporting for different destinations#

• Desktop FDM slicer: 3MF, Medium or High refinement.
• Resin slicer: 3MF or STL, High refinement, because detail shows in fine layers.
• Service bureau: ask which format; send STL/3MF at fine tolerance, plus STEP if accepted.
• Metal PBF: ask the vendor; STEP is often preferred, or use a fine mesh (general guidance).
• Rendering or other CAD: OBJ or STEP; do not use STL for editing downstream if you can avoid it.

Verifying the export#

1. Open the file in the slicer or a viewer.
2. Confirm the bounding box matches the dimensions in Fusion (use Inspect > Measure to confirm).
3. Zoom into curved surfaces. Visible flats mean the refinement is too low.
4. Run the slicer's mesh error check (non-manifold edges, holes, flipped normals).
5. Check file size. A simple part should be under a few MB; massive files may indicate over-refinement.

Options reference#

The help does not list default values or units for these fields; read them in the dialog.

Choosing refinement#

Mesh refinement is a trade-off between smoothness and size. The following is general guidance, not Autodesk data:

• Surface deviation should be much smaller than your layer height; 0.01-0.03 mm is plenty for FDM, and 0.005-0.01 mm for resin or small precision parts.
• Normal deviation controls how smooth a curve looks; a lower angle gives smoother curves but more triangles.
• Maximum edge length matters for large nearly-flat surfaces that curve slightly: without a cap, the triangulation uses huge triangles whose midpoints deviate.
• Aspect ratio keeps triangles from becoming long slivers, which cause slicer errors.

If a body is very large (a 500 mm part), a surface deviation of 0.01 mm may generate a massive mesh; relax to 0.02-0.05 mm and check.

STL versus 3MF at a glance#

Tips and pitfalls#

Tip: Default to 3MF unless a tool refuses it. It avoids unit mix-ups and carries multiple parts neatly.

Warning: Do not export STL, edit it and expect to bring changes back to Fusion cleanly. Meshes lack parametric history. Edit the Fusion model and re-export.

Warning: Do not use extremely low refinement to make files small; circles become visible polygons and holes become undersized, because the mesh vertices lie on the circle and the facets cut inside it. Holes can lose a noticeable fraction of a millimeter at low refinement.

Tip: Large lattices and organic shapes create heavy meshes. Use the mesh reduction tools described in the mesh-repair page if the slicer chokes.

Warning: Binary STL files are safe to share, but ASCII STL files can be many times bigger. Choose binary.

Tip: For multicolor printing, export 3MF or OBJ with appearances if your slicer supports it, and verify that Fusion writes the color information for your version.

Warning: Hidden or suppressed bodies might be skipped, or surprising bodies might be included. Always open the output and count the objects.

Tip: Keep a "last exported" folder and clear it periodically. Old exports are a common cause of printing the wrong revision.

Practice exercise#

Model a 30 mm diameter, 10 mm tall cylinder with a 5 mm hole. Export it three times as STL with Low, Medium and High refinement. In your slicer, view each at high zoom and use a measuring tool (if present) on the hole. Then export it as 3MF at Medium. Expected result: Low shows a polygonal circle and a hole noticeably smaller than 5 mm in measurement, Medium and High are visually round with holes close to 5 mm. File sizes rise from Low to High. The 3MF imports at the correct size without a unit prompt, while an STL might ask about units in some slicers.

Related#

• The 3D Print Command and Sending to a Slicer
• Preparing Models for Printing
• Mesh repair, reduce and remesh (07-form-sculpt-mesh)
• Mesh workspace and import (07-form-sculpt-mesh)

Common export problems and fixes#

The slicer reports holes or non-manifold edges. Usually caused by a surface body that is not closed, or overlapping solids. In Fusion, check each exported item's icon in the Browser to confirm it is a solid, and combine overlapping bodies. If the body came from an imported mesh, repair it in the Mesh workspace first.

The exported file is huge. Over-refined tessellation of large or highly curved bodies, or lattices, produce millions of triangles. Raise the surface deviation modestly, set a sensible normal deviation, and avoid exporting detail you do not need. Mesh reduction in the Mesh workspace is a fallback.

Curved surfaces look faceted in the print. Refinement was too low, or the slicer's resolution setting is simplifying the mesh. Re-export at High and look for a slicer option that limits resolution (some slicers have a maximum resolution setting that merges tiny segments).

Holes measure undersized. Mesh vertices lie on the true circle, so the flat facets sit inside it; low refinement shrinks holes. Raise refinement, and still compensate in the design with a clearance parameter because the printer adds its own error.

The part opens at the wrong size or rotated. Check the unit choice and the Fusion document's orientation settings; export 3MF to reduce unit ambiguity.

Colors are missing. STL cannot carry color. Use 3MF or OBJ if your slicer supports them, and verify in your version that Fusion writes appearance data into that format.

Wrong revision printed. Use version suffixes, or export from the Data Panel version you intend. Fusion's own versioning keeps older design versions available, so you can regenerate an earlier export if needed.

A recommended export routine#

1. Confirm units in Document Settings.
2. Verify every body is solid and combined as intended.
3. Name the bodies meaningfully.
4. Export 3MF at Medium or High refinement (High for resin and metal).
5. Open the file in the slicer, check bounding box, error report and smoothness.
6. Also export a STEP file into the project folder as an archival, process-independent record.
7. Keep the exported file next to the design, and record the refinement values in a note if you tuned custom values.