Overview#
Meshes straight from a scanner or a download are often too dense, contain holes, or have bad geometry such as duplicate or flipped triangles. Three tools prepare them:
- Repair closes holes and fixes defects so the mesh is watertight.
- Reduce lowers the triangle count while preserving shape.
- Remesh replaces the triangulation with a new, more even one. It can also regenerate triangles to a target density.
Doing these in the right order matters: repair first, then reduce or remesh, then convert.
Where to find it#
Design workspace > Mesh tab:
- Prepare > Repair (you can also click the warning icon next to a mesh body in the browser). Prepare also holds Generate Face Groups and Combine Face Groups.
- Modify > Reduce.
- Modify > Remesh.
- Related Modify tools: Smooth, Separate, Reverse Normal, Combine, Plane Cut, Shell, Convert Mesh, Direct Edit and others. Erase And Fill and Mesh Align are only available in Direct Edit in Parametric mode or in Direct Modeling mode.
Step by step#
Repair#
- Select Mesh > Prepare > Repair.
- Pick the mesh body.
- Choose the Type, from least to most invasive: Close Holes (fixes flipped triangles and closes holes, fastest), Stitch and Remove (also stitches triangles and removes double triangles, degenerate faces and tiny shells), One Touch Fix (a combination that also tries to resolve self-intersections and non-manifold edges), Wrap (everything in Stitch and Remove, plus wrapping the surface; inner structures are destroyed) and Rebuild (reconstructs the mesh; inner structures are destroyed; slowest).
- For Rebuild choose the rebuild type: Fast, Preserve Sharp Edges, Accurate (adds Offset and Adaptive) or Blocky, and set the Density. In Detailed Analysis you can adjust the Small Shell Threshold and Degenerate Threshold.
- Use Preview (unchecked shows the original with analysis; checked shows the repaired result) and read Quick Analysis: closed, oriented and positive volume.
- Click OK, and repeat with a stronger type if issues remain.
Reduce#
- Select Mesh > Modify > Reduce.
- Select the mesh body.
- Choose the Type:
- Tolerance: the maximum deviation from the original, in design units. Best for accuracy-driven work.
- Proportion: the percentage of faces to keep.
- Face Count: the exact number of faces to produce.
- For Proportion and Face Count, choose the Remesh Type: Adaptive keeps small faces in detailed areas and large faces in simple areas; Uniform makes faces similar in size. (The Remesh Type field does not appear for Tolerance.) You can select a whole body or face groups.
- Use Preview to see the result live, then click OK. A Reduce feature is added to the timeline; right-click it and Edit Feature to change the settings later.
Remesh#
- Select Mesh > Modify > Remesh.
- Select the mesh body or specific face groups.
- Choose the Type: Adaptive (smaller faces in detailed areas) or Uniform (similar faces everywhere), and set the Density, which controls the number of faces created.
- Set Shape Preservation for how much of the original shape is kept, and tick Preserve Sharp Edges and Preserve Boundaries if those features must survive.
- Use Preview, then click OK.
Use Remesh for: evening out sliver triangles that confuse conversion, regenerating a clean mesh after a boolean or sculpt, or converting a mesh with uneven density into uniform triangles for shelling.
Options reference#
| Option | What it does | Notes/default |
|---|---|---|
| Repair Type | Close Holes, Stitch and Remove, One Touch Fix, Wrap, Rebuild | Wrap and Rebuild destroy inner structures |
| Rebuild type | Fast, Preserve Sharp Edges, Accurate, Blocky | Accurate adds Offset and Adaptive |
| Small Shell / Degenerate Threshold | Largest shell or degenerate face to repair | In Detailed Analysis |
| Reduce: Tolerance | Max deviation allowed | Units of design; smaller means more triangles |
| Reduce: Proportion | Percentage of faces kept | 100 percent is no change |
| Reduce: Face Count | Target number of triangles | |
| Reduce: Remesh Type | Adaptive or Uniform | Only for Proportion and Face Count |
| Remesh: Type | Adaptive or Uniform | |
| Remesh: Density | Number of faces created | Higher density, more faces |
| Remesh: Shape Preservation | How much original shape is kept | |
| Remesh: Preserve Sharp Edges / Boundaries | Keeps sharp edges and open boundaries | Tick for hole-edged meshes |
| Smooth: Smoothness | 0 (minimal) to 1.00 (maximum) smoothing | Over-smoothing removes real detail |
| Reverse Normal | Flips orientation | Whole body or face groups via Mesh > Modify; individual faces via Direct Edit |
Tips and pitfalls#
Tip: Before Repair, check whether the problem is genuinely holes. A scan of a part with real openings (a pipe, a through hole) should not be filled. Use Erase and Fill on selected regions instead of an automatic fill of everything.
Tip: Reduce in steps (for example 50 percent, then another 50 percent if needed). Compare using Inspect > Measure at key features. Excess reduction rounds corners and deviates from the true shape.
Tip: General guidance, not an Autodesk limit: for conversion to BRep, aim for roughly 10,000 to 50,000 triangles for typical hand-sized parts. More makes conversion slow; fewer loses detail.
Warning: Reduce and Remesh are not reversible except via timeline rollback or undo. Duplicate the mesh body first (Copy/Paste New) if you want to compare.
Warning: Scan data often contains noise: spikes and thin floating shells. Use Separate to split shells and delete the junk before reduction; otherwise Reduce will faithfully preserve the noise.
Tip: After Reduce, run Repair again. It's common for decimation to introduce a few bad triangles.
Warning: A watertight mesh is not necessarily a valid solid: self-intersections can remain after Repair. If conversion or slicing fails, try Remesh to rebuild the surface, which often removes self-intersections.
Tip: Remesh can change the shape of thin features (general guidance); use Shape Preservation and check thin walls afterward.
Choosing the right Repair type#
Pick the least invasive type that clears the Quick Analysis warnings, because every step up in strength changes more of your mesh.
| Mesh condition | Start with | Escalate to | Cost |
|---|---|---|---|
| A few small holes, otherwise good | Close Holes | Stitch and Remove | Minimal change |
| Duplicate triangles, slivers, floating specks | Stitch and Remove | One Touch Fix | Small shells vanish |
| Self-intersections or non-manifold edges | One Touch Fix | Wrap | Wrap destroys inner structures |
| Messy scan with internal junk | Wrap | Rebuild | Slowest, reconstructs everything |
Wrap and Rebuild are the only types that cure severe self-intersection, but they wipe out any internal cavities, so a hollow part loses its cavity. If a mesh has an intentional hollow, repair with Stitch and Remove or One Touch Fix and keep the hollow.
Worked example: a scanned bracket#
The numbers here are illustrative. A 300,000 triangle scan of a bracket reports not closed and has 14 tiny floating shells. Run Stitch and Remove first, with a Small Shell Threshold that discards the specks (about 1 mm). It closes most gaps but leaves two self-intersections. One Touch Fix clears both. The result is closed, oriented and positive volume. Reduce then brings the count to 40,000 with Tolerance 0.05 mm, a safe target for conversion.
Reduce and Remesh: when to use which#
Use Reduce when you want fewer triangles with the least deviation. Use Remesh when you want a different triangulation, for example evenly sized triangles for Shell or conversion.
| Goal | Tool | Settings to start with |
|---|---|---|
| Lighten a heavy mesh with accuracy limits | Reduce, Tolerance | 0.05 to 0.1 mm for hand-sized parts (general guidance) |
| Hit a face budget | Reduce, Face Count, Adaptive | 20,000 to 50,000 for conversion (general guidance) |
| Cut by a fixed ratio | Reduce, Proportion | 50 percent, repeated if needed |
| Even sliver triangles before conversion | Remesh, Uniform | Moderate density; Preserve Sharp Edges on |
| Keep detail while thinning flat areas | Remesh or Reduce, Adaptive | Check small features afterward |
Reduce with Tolerance is the safest because the deviation is bounded. A tolerance of 0.1 mm on a 100 mm part is 0.1 percent, below most FDM printing accuracy. Proportion and Face Count have no bound on deviation, so check key dimensions after using them. You can also reduce only selected face groups, which protects areas such as bearing seats while thinning decorative surfaces.
Smooth, Erase And Fill and Separate#
- Smooth (Modify) takes a single Smoothness value from 0 to 1.00. Use it to soften rough areas or sharp creases, in small doses, on a copy.
- Erase And Fill is available in Direct Edit only (Parametric mode) or in Direct Modeling mode. Select faces (double-click a face on a hole boundary to select the whole boundary); choose Uniform (regular faces, with a Density) or Minimal (fewest faces, often long thin triangles). This is the tool for deliberate local patching, instead of an automatic Repair.
- Separate splits a mesh into independent bodies; the Type is Mesh Shells, All Face Groups or Select Face Groups, and Keep Body preserves a copy of the original. Use it to peel off noise shells.
Common failures and fixes#
| Symptom | Cause | Fix |
|---|---|---|
| Repair reports success but conversion still fails | Self-intersections remain | Use One Touch Fix, then Wrap or Rebuild |
| Hollow part lost its cavity | Wrap or Rebuild destroys inner structures | Use a milder type |
| Reduced mesh has bad triangles | Aggressive decimation | Run Repair again after Reduce |
| Reduce loses sharp edges | Uniform remesh type keeps faces even rather than preserving detail | Use Adaptive or a smaller Tolerance |
| Remesh changes thin walls | Shape Preservation too low (general guidance) | Raise Shape Preservation; check thin walls afterward |
| Operation is slow | Mesh too large | Reduce first or work in a scratch design |
Practice exercise#
Clean up a noisy mesh with measurable results.
- Insert a scan-like STL (any figurine mesh above 200,000 triangles) and note the triangle count.
- Open Prepare > Repair and read Quick Analysis. Try Close Holes first, then undo and compare with Stitch and Remove. Record which warnings each clears.
- Use Reduce with Tolerance 0.1 mm. Record the face count. Undo and try Proportion 20 percent with Adaptive. Compare the face counts and the shape.
- Measure one key dimension (for example overall length) on the original and on each reduced version. Record the differences.
- Run Remesh with Uniform type at moderate density, with Preserve Sharp Edges on, and compare edges visibly.
- Run Repair again on the final mesh and confirm Quick Analysis shows closed, oriented and positive volume.
Expected result: a lighter, watertight mesh with measured deviations under a fraction of a millimetre, a table showing which Repair type fixed which problem, and a clear understanding that Tolerance gives bounded deviation while Proportion does not.
Related#
- Mesh workspace and import
- Mesh shell and plane cut
- Converting a mesh to BRep