Prepare a CAD file for exact weight and stones
Save in millimetres with render meshes (never Save Small), mesh finely, make every metal part and stone a closed solid, put stones and metal on clearly named layers, hide or delete cutters, keep one object per stone, cut the stone seats into the metal, model bands at one base size and give every head its centre stone. A file that breaks a rule gets a plain warning, and a weight that can't be trusted is not published.
3D Jewelry Designer4 min read
The checklist
- Work in millimetres. In Rhino, Document Properties, Units, set Model units to Millimeters.
- Save with render meshes. Use a normal save, never Save Small: the weight is read from the render meshes stored in the file.
- Mesh finely. A custom render mesh with Maximum distance, edge to surface of 0.002 to 0.005 mm, Jagged seams off and Refine mesh on. Re-mesh the objects, then save.
- Make every part a closed solid. Each metal object and each stone is a closed polysurface or solid, with no naked edges.
- Name the metal and the stones. Put stones on a layer, or give them a name, with a word such as Diamond, Gem, Stone, Sapphire, Brilliant, Melee or Pave. Put metal on layers named Metal, Gold, Platinum, Shank, Prong, Bezel, Basket, Gallery, Mount or Setting.
- Hide or delete cutters. Boolean tools, seat cutters and helper solids.
- One object per stone. Use gem-tool objects or block instances, and don't join stones into one mesh.
- Cut the seats. Each stone sits in a seat already cut out of the metal.
- Model every band at the same base ring size.
- Give every head a centre stone.
Why each rule matters
| Rule | What goes wrong without it |
|---|---|
| Millimetres | A file saved as centimetres but drawn in millimetres arrives ten times too large. |
| Render meshes | Objects with no mesh are skipped and counted, and a band with no meshes has no weight. |
| Fine mesh | A render mesh always reads a little small, and a coarse one reads low. Jagged seams leave joined surfaces open. |
| Closed solids | Volume needs a closed surface, so open metal publishes no weight, and an open stone can't be measured. |
| Names | Metal and stones are told apart by layer and object names first. A gem word wins over a metal word. |
| Cutters | Every visible object is weighed, and an unnamed solid usually counts as metal, so a visible cutter adds weight with no warning. |
| One object per stone | The stone count is the number of stone objects. Joined stones are split where they can be, so check the count. |
| Cut seats | Nothing is subtracted for stones, so metal left inside a seat adds weight with no warning. |
| One base size | Weights are given at the size the band was modelled at, and siblings should match. |
| Centre stone | On a head the largest stone is the centre stone and is left out of the side-stone count. |
Mesh settings in Rhino
Select the objects and, in their Properties under Render Mesh, turn on a custom mesh and adjust it: Maximum distance, edge to surface between 0.002 and 0.005 mm, with Jagged seams off and Refine mesh on. Re-mesh, then save with the normal Save. Save Small removes the render meshes, and the file then has nothing to weigh.
What is left out, and units
Hidden objects and objects on hidden layers are left out of the model and the weight, including the children of a hidden parent layer. Curves, points and other non-solid objects are skipped and counted.
A file saved in centimetres, inches or another unit is converted to millimetres. A file with no unit, or custom units, has its unit worked out from its geometry, and only when exactly one unit gives stones and a finger hole of believable sizes; otherwise it is marked Units unknown and no weight is published. Saving in millimetres avoids the guesswork.
Reading the warnings
| Warning | Fix in the model |
|---|---|
| Units unknown or Units inferred | Set Model units to Millimeters. |
| Metal not watertight | Close the polysurface (ShowEdges finds naked edges), re-mesh and save. |
| No metal | Check the layer and object names. |
| Stone can't be measured | Close the stone, and check the scale and the names. |
| Objects skipped | Save with render meshes, and remove curves and loose points. |
| Coarse mesh | Re-mesh with a smaller edge-to-surface distance. |
| Joined stones | Make one object per stone. |
| Shape unknown | Model the stone with its true outline; its carat then comes from its volume. |
| Centre stone unclear or Centre carat differs | Model one clear centre stone, and check the carat in the part's name. |
Several large stones (a three-stone or toi-et-moi ring) and Shank varies, No plain shank or Eternity band on a stone-set band are notes, with nothing to fix.
What the weight is
It is the exact CAD metal weight, at the alloy's density, at the size the band was modelled at. No casting shrinkage or finishing allowance is added, so a finished ring on a scale can weigh a little under it. Carats are diamond carats, whatever the gem: a round stone's comes from your stone size chart by its girdle diameter, and other shapes from their measured length, width and depth. Weight, stones and cost-based pricing explains how the numbers are used.
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