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Non-manifold edges,split apart and counted to zero.

When three or more triangles meet at one edge, a slicer cannot tell inside from outside. MeshMedic finds those edges and any bow-tie corners, separates them into clean shells, and reports a before and after count for every part.

Open the file, read the Non-manifold edges row, choose Repair, and export once the After column reads 0 and the status says Fixed.

Pay once. Own it forever.

One-time purchase on the Microsoft Store · No subscription · Instant install

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Buy through the Microsoft Store—instant install, automatic updates, and a Microsoft receipt for easy expensing. No account needed on our site, and no subscription on Store purchases.

Full MeshMedic overview
One-time purchase No telemetry Local-first

windows · originals never overwritten · 3mf colors kept · nothing uploads

If this sounds like your week

Two bodies touching along one edge confuse every slicer.

Non-manifold geometry usually comes from bodies that were placed against each other instead of joined: two blocks kissing at a corner, a handle pushed onto a mug without a union, or a lattice whose struts share single lines. Where three or four faces hang off one edge, there is no clear answer to which side is solid, and slicing software has to guess.

Where tooling usually breaks

The guess shows up as missing walls or stray extrusions.

One slicer drops a thin wall, another bridges across a gap that should stay open, and a third refuses the model outright. Hunting the offending edge by eye in a dense mesh is slow, and deleting faces by hand tends to open fresh gaps beside the ones you were chasing. Without numbers taken before and after, nobody can say whether the problem is truly gone.

Where MeshMedic lands

Split the shared edges so each surface stands on its own.

MeshMedic separates every over-shared edge and bow-tie corner by duplicating the vertices involved, so each surface keeps its own boundary. Afterward each shell is turned to face outward. The Non-manifold edges row shows the starting number, the remaining number, and a status, and the note lists how many vertices were split.

Pay once. Own it forever.

One-time purchase on the Microsoft Store · No subscription · Instant install

Get it from Microsoft

Buy through the Microsoft Store—instant install, automatic updates, and a Microsoft receipt for easy expensing. No account needed on our site, and no subscription on Store purchases.

Learn more about MeshMedic

windows · originals never overwritten · 3mf colors kept · nothing uploads

What you get

Feature highlights

Every defect counted

non-manifold edges, inverted triangles, and holes for every part, in a table with Before, After, and Status columns, and No defects found for a clean file.

One repair pass

welds coincident vertices, removes degenerate and duplicate triangles, splits non-manifold edges and vertices, orients every shell outward, and caps holes.

Every change shown in 3D

triangles the repair flipped or added turn blue, and Show before switches back to the mesh as it was, with inverted triangles in red.

3MF projects kept intact

colors, materials, components, build items, metadata, and the thumbnail come through, and only the repaired mesh is rewritten.

A before and after note

the counts for every part and the triangles flipped, added, and removed, ready to copy or save as a .txt file for the job.

Originals never overwritten, nothing uploaded

every export is a new file in the same format, and the app makes no network connections and has no account.

Especially when

  • Repair holes, non-manifold edges, and inverted triangles in an STL, OBJ, or 3MF without rebuilding the model in CAD
  • See exactly what a repair changed, with counts before and after and every changed triangle shown in 3D
  • Repair a 3MF in place, keeping its colors, materials, components, and plate layout instead of converting it to STL
  • Keep customer and client models on the PC, with no upload, no account, and the original file never overwritten

Who benefits

Real-world scenarios

Two boxes touching along one edge

A designer arranged two boxes edge to edge for a display stand and exported them as one STL. The slicer reports non-manifold edges along the line where the boxes meet.

MeshMedic counts the shared edges in the Non-manifold edges row. After Repair the row reads 0 and Fixed, the two boxes become two closed shells, and the note records how many vertices were split to separate them.

A pinched corner in a sculpted model

A sculpted figure has two limbs that meet at a single vertex. The corner is easy to miss in a viewer, but it pinches the surface at one point and the slicer flags the model.

The repair splits the pinched vertex so each limb has its own corner and orients both surfaces outward. The note lists the split vertex count for that part, so the change is on record when the model goes back to the sculptor.

Several named groups in one OBJ

A part exported as OBJ holds several named groups, and only one of them picked up non-manifold edges after a quick edit. The rest of the file has to stay organized by group.

MeshMedic reads each OBJ group as its own part, so the table shows which group holds the problem edges. The export keeps the objects, groups, materials, and smoothing groups, with the repaired mesh in place.

Deep dive

How MeshMedic resolves a non-manifold edge

What counts as non-manifold. In a closed surface, every edge belongs to exactly two triangles, one on each side. MeshMedic counts an edge as non-manifold when three or more triangles share it. A bow-tie vertex is the corner version of the same problem: two surfaces that touch at a single point.

Why welding comes first. STL keeps three separate corners for every triangle, so two faces that look joined may not share anything in the file. MeshMedic welds corners at the same position before it counts, so the table reflects the real connections, and the number of welded vertices appears in the note.

Splitting, not deleting. The repair separates a non-manifold edge by giving each surface that meets there its own copy of the edge's vertices. Bow-tie corners are split the same way. The split step removes no triangles, so the shape in the preview is the shape you started with, now as separate surfaces.

Orientation afterward. Once the surfaces are separate, each shell is walked across its shared edges and turned so its triangles face outward. A closed shell that was inside out is flipped as a whole. Those flips are counted in the Inverted triangles row and drawn in blue in the preview.

Reading the result. The Non-manifold edges row shows the Before count, the After count, and a status: None when there were none, Fixed when the After count is 0. With several parts, each part gets its own rows, labeled with the part name, so you can see which object or group held the problem.

The record. The note lists the counts before and after for every part, plus vertices welded and vertices split. Save note writes it as a .txt file to keep with the job or to send to the person who made the model.

The file you get. Export writes the same format you opened, as a new file under a name you choose. STL stays STL, OBJ keeps its objects, groups, and materials, and a 3MF keeps its colors, materials, components, and build items.

How it is built

Built to change the mesh and nothing else.

Originals never overwritten

Every export is a new file you name. Saving over the original is refused, even through a junction, a hard link, a network path, or after the original was renamed or moved.

The rest of the 3MF untouched

Other entries in a 3MF package are copied byte for byte, and inside the model only the repaired vertices and triangles are replaced, so colors, materials, components, and build items come through.

Nothing uploads

MeshMedic runs in the Windows app sandbox with no declared capabilities, makes no network connections, and has no account and no telemetry. One-time purchase in the Microsoft Store.

FAQ

Straight answers—no glossary dump

What is a non-manifold edge in an STL?

An edge shared by three or more triangles. In a well-formed solid every edge belongs to exactly two triangles, one on each side, so software can tell inside from outside. Non-manifold edges usually appear where separate bodies touch along a line or where faces were stacked during editing. MeshMedic counts them for each part in the Non-manifold edges row before you repair anything.

How does MeshMedic fix non-manifold edges?

It splits them. The vertices along each over-shared edge, and any bow-tie corner where two surfaces touch at a point, are duplicated so each surface gets its own boundary. Then each shell is oriented to face outward. The table shows the Non-manifold edges count before and after, and the note records how many vertices were split and welded.

Can I see which part of a file has the problem?

Yes. Every part gets its own rows in the table, labeled with its name: one part for an STL, one for each group or object in an OBJ, and one for each mesh object in a 3MF. The Before column shows where the non-manifold edges are, and the After column and the status show what the repair resolved.

What happens to my original STL, OBJ, or 3MF file?

It stays exactly as it was. MeshMedic reads the whole file into memory when you open it and writes every repair to a new file you name in the Windows save dialog, with the original name plus -repaired suggested. Saving over the original is refused, even when you reach it through a shortcut folder (junction), a hard link, a network path, or after it was renamed or moved. You can repair the same original as often as you like.

Where do my files go, and how do I get MeshMedic?

They stay on your PC. MeshMedic runs in the Windows app sandbox with no declared capabilities, makes no network connections, has no account, and collects no telemetry. It opens only the files you pick and writes only the files you save. MeshMedic is a one-time purchase in the Microsoft Store, and the Store runs a 15-day free trial with every feature, so you can repair your own files before you buy.

Related pages

Repair a broken STL file, and see every change first. Fix the mesh errors before the slicer has to guess. Repair the mesh inside a 3MF, and keep everything else.

A broken STL or 3MF in.
A repaired file out, with every change shown.

MeshMedic counts holes, non-manifold edges, and inverted triangles, repairs them in one step, shows every changed triangle in 3D, and writes a new file in the same format, with a 3MF’s colors and components kept. Originals are never overwritten, nothing uploads, and the Microsoft Store runs a 15-day free trial.

Pay once. Own it forever.

One-time purchase on the Microsoft Store · No subscription · Instant install

Get it from Microsoft

Buy through the Microsoft Store—instant install, automatic updates, and a Microsoft receipt for easy expensing. No account needed on our site, and no subscription on Store purchases.

Open full product page

Technical specifications

Technical specifications for procurement

Spec Implementation
Data Sovereignty Reads only the STL, OBJ, or 3MF files you pick in the Windows open dialog; writes only the repaired file and the optional .txt note you name in the save dialog, refusing to save over the original by any path; the Recent list stays in the app’s own storage on this PC
Telemetry Status None; no account, no telemetry, and no network client in the app
Core Runtime .NET 10 and WinUI 3 (Windows App SDK 2.5), packaged as MSIX and run in an AppContainer with no declared capabilities; repair engine and STL, OBJ, and 3MF readers and writers in managed C#; 3D preview drawn with Direct3D 11
Network Requirements Fully functional offline; the package declares no capabilities, including no internet access, and the app makes no network connections
Deployment Compatibility Windows 10 version 2004 or later and Windows 11, x64; one-time purchase on the Microsoft Store with a 15-day free trial
Inputs STL (binary and ASCII), OBJ, and 3MF, picked in the Windows open dialog or reopened from the Recent list of the last 25 files
Checks Non-manifold edges, inverted triangles, and holes for every part, plus degenerate and duplicate triangles; Before, After, and Status columns; No defects found for a clean file
Repair Welds coincident vertices, removes degenerate and duplicate triangles, splits non-manifold edges and bow-tie vertices, clears stray fragments, orients every shell outward, and caps holes
Preview 3D view with repaired and added triangles in blue, inverted triangles in red, and a Show before toggle; orbit and zoom with the mouse or the keyboard
Outputs A new file in the same format: STL in its original binary or ASCII flavor; OBJ with objects, groups, materials, and smoothing groups; 3MF with colors, materials, components, build items, metadata, and thumbnail kept; plus a before and after note to copy or save as .txt
System Direct3D 11 graphics recommended, with software drawing as a fallback; about 1 GB of available memory per million triangles, and 8 GB of RAM covers meshes up to about 5 million triangles in binary STL, 3MF, or OBJ