Choosing between options
STEP, STL or 3DM — which should you export for rendering?
Every jewellery CAD program can write all three, and they are not interchangeable for rendering. One carries the stones, one carries exact curves, and one is a print file that has lost most of both. Here is what each keeps, what each loses, and which to choose when.
3DM: the one with the stones
Rhino's native format. Layers become parts, units are kept, and — the decisive point — a jewellery 3DM usually records where each stone sits as an object even when no stone mesh was saved. The studio reads those positions and places real gems in them. No other format carries this. It is read with McNeel's own library, so no Rhino is needed to render it.
What it does not carry: Rhino's own materials, which are Rhino's business — you choose gold and diamond in the studio.
STEP: the one with exact curves
The neutral CAD format every program writes. It carries exact surfaces, which the studio tessellates through a real geometry kernel at a tolerance tuned for jewellery — so a band renders as a curve, never as flats. It keeps parts separate, and AP214 or AP242 keeps colours and names too. It does not carry stone positions; if the stones are modelled as solids they arrive as parts and the studio finds them, but empty seats stay empty.
STL: the one for printing
A single mesh of triangles with facet normals and nothing else. No parts, no names, no units, no colours — and for jewellery, usually no stones, because a print does not need them. The studio welds it, smooths it and splits it wherever shells do not touch, which recovers a lot. What it cannot recover is curvature the export left out, or stones the export omitted. Those go back in by hand.
Side by side
What each format carries into the render:
- Exact curves — STEP yes, 3DM yes, STL only as fine as the export
- Separate parts — STEP yes, 3DM yes (layers), STL recovered where shells do not touch
- Stone positions with no stone meshes — 3DM only
- Part names and colours — STEP AP214 yes, 3DM partly, STL never
- Units — STEP yes, 3DM yes, STL none
- Reads without the original program — all three
The recommendation
For a piece with stones, export 3DM. For metal-only, STEP or 3DM — they render alike. Export STL only when it is what you have; it renders well, but you will place the stones yourself and you cannot add curvature back. If a casting house or client sent you an STL and you can ask for the 3DM, ask. 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
Which format renders diamonds best?
The renderer is the same for all three; what differs is whether the stones arrive. A 3DM places them from the file. A STEP brings them if they were modelled as solids. An STL has usually lost them and they are placed by hand.
Is STEP or 3DM more accurate?
Equally accurate on the metal — both carry exact geometry and both are tessellated finely by the studio. 3DM additionally carries stone positions, which is why it is the better choice for a set piece.
Can I convert an STL back to STEP?
Not meaningfully — the curvature is gone. Render the STL as it is, and get the STEP or 3DM from the source if you need the curves.
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