What the studio does automatically
How a single STL becomes separate parts
An STL is one blob of triangles — no parts, no names, and faceted shading baked in. Drop it in and, before you see it, it has been taken apart: the band, the head and each stone that touches nothing else are separate parts again, and the surface reads as polished metal rather than a print file. Here is what happens in those first seconds and why.
1. The facet normals are thrown away
STL stores a normal per triangle, which is what makes a print file look faceted. Those normals also block welding: two triangles that share an edge in space are stored with separate copies of the shared vertices, and the per-facet normal keeps them separate. So the first step is to drop them.
2. Vertices are welded at a tolerance that scales
Duplicated vertices are merged so the mesh becomes connected. The tolerance is not a fixed number — exporters emit floating-point jitter far above a fixed tiny threshold on millimetre-scale jewellery, and every unwelded seam would break the smoothing. It is set relative to the model's size, so a ring and a building weld correctly with the same code.
3. Smooth normals are rebuilt
With the mesh connected, normals are recomputed from the surrounding triangles, which is what turns flats into a continuous surface. This is smoothing of the shading, not of the geometry: a coarse export's flats are still there in the silhouette, and no smoothing can add curvature the file did not include. Export finer, or use the STEP.
4. Disconnected shells become parts
The mesh is walked to find its connected components — sets of triangles joined through shared vertices, matched by rounded position so shells that merely duplicate coordinates still connect. Each component becomes a part. A band, a head and four separate stones export as one STL and come back as six parts; two links of a chain that physically interlock stay as one, because they are one connected surface, and for rendering that is right.
- Facet normals dropped
- Vertices welded, tolerance relative to model size
- Smooth normals rebuilt — shading, not geometry
- Connected components split into parts
The same for PLY, VTK and Draco
Every single-mesh format gets this treatment. Formats that carry their own parts — STEP, 3DM, OBJ groups, glTF, 3MF — keep them and skip the split. Everything here happens on your own machine: the file is converted and rendered in the browser through your GPU and is never uploaded, so an unreleased design stays unreleased.
Questions
Why is my STL one part when it should be several?
The bodies touch or overlap in the mesh, so they are one connected surface. Export them as separate STL files, or as 3MF, which keeps objects separate — or use STEP, which never fuses parts.
Can smoothing fix a coarse STL?
It fixes the shading, so the surface no longer shows a facet per triangle. It cannot fix the silhouette — the flats along a band's edge are geometry, and only a finer export or the STEP has the curve.
Does welding change the shape?
No. It merges vertices that are already at the same position (within the jitter an exporter introduces); it does not move anything.
Free · runs in your browser · your file is never uploaded