CAD and 3D Rendering in Custom Jewelry: What You Approve

A CAD rendering can be approved in a meeting and disappointed in the hand, because the image carries no information about thickness, weight or height. What is actually being approved is a set of dimensions: wall thicknesses, setting height above the finger, band profile, total metal volume and therefore weight. Beautiful renders hide bad numbers, which is why the useful approval routine is to ask for the measured values and read them rather than to look at the picture again.

What should you actually approve on a CAD model?

The dimensions and the weight, with the rendering as an illustration of them.

Five numbers matter on almost every piece: the overall dimensions, the wall or band thickness at its thinnest point, the setting height, the prong thickness, and the estimated metal weight. Those five determine durability, comfort and cost, and none of them is visible in a rendering. A model that looks correct and has a 0.5 mm wall at the thinnest point will bend in wear; one that looks identical with a 0.9 mm wall will not.

Ask for the numbers in writing alongside the render, and compare them against the wear the piece will receive.

The values to demand

Six measurements, and what each controls.

Value	What it controls	Watch for
Overall dimensions	How large the piece reads, and fit	Whether the figure includes the bail or the clasp
Minimum wall or band thickness	Structural integrity in wear	Under about 0.8 mm on a daily-worn ring
Setting height	Comfort and snag risk	A tall basket on a ring worn with other rings
Prong thickness	How well the stone is held	Thin claws designed for appearance
Estimated metal weight	Cost and how the piece feels	A design that looks compact and weighs heavily
Stone seat depth	Whether the stone sits properly in the metal	A seat too shallow to grip the girdle

Why a rendering looks better than the finished piece

Four systematic reasons, all of them predictable.

Renderings are lit to flatter, so surfaces read brighter and cleaner than polished metal. Reflections are perfect, which makes a curved surface look smoother than it will be after hand finishing. There is no sense of scale, so a piece can look larger than it is. And there is no weight, which is the property clients notice first when they pick a piece up.

All four are addressed by the same measure: ask for dimensions and weight, and put the render in front of a ruler rather than on a full screen.

What the CAD stage is good for

It is the cheapest place to make every structural change.

Proportion adjustments, band width changes, setting type changes and outline refinements all cost design time at CAD and nothing at the bench. Once a mould exists, the same change requires a new mould. That asymmetry is why revisions belong at this stage and why approving a model quickly — but on the numbers rather than on the picture — is the behaviour that keeps a custom order on schedule and on budget.

Our notes on the custom design process set out how the CAD stage sits between the brief and the sample.

The transition from model to sample

Everything the model cannot show is settled by the sample.

Weight in the hand, how a band sits against the neighbouring fingers, whether a setting catches on fabric, how a finish reads on real metal, and how a piece hangs rather than how it is positioned for a render. The sample is also where fit is confirmed on the wearer, since a CAD model cannot answer whether a ring passes over a knuckle comfortably.

The sample should be produced to the same method as production. A sample that is hand-finished to a higher standard than the order will be sets a standard the order cannot meet, which is a common source of disappointment in custom work.

What a lower-quality CAD process looks like

Five signals worth noticing before approving.

A model supplied only as an image with no dimensions. A single view, when a piece needs front, side and three-quarter views to be judged. No estimated weight. Wall thickness quoted as a range rather than a minimum. And a model revised without the previous version recorded, so the client cannot tell what changed between revisions.

None of these makes the model wrong, and all of them make it unverifiable — which is the condition that produces a piece nobody can check against what they approved.

How to run the approval

Five steps that take ten minutes.

Request the dimensions and weight in writing with the render. Check the minimum thickness against how the piece will be worn. Check setting height against the fingers or the neckline it will sit against. Compare the overall dimensions against something physical of the same size. And record the approved revision number, so the version that goes to production is the version that was signed off.

That last step is the one that prevents the most arguments, because it makes the approved version unambiguous.

Sources and further reading

• GIA 4Cs — how stone dimensions feed a design
• Assay Office — hallmarking requirements for finished pieces
• The Silver Institute — metal behaviour and section thickness
• CIBJO Blue Books — terminology and disclosure
• International Gem Society — setting geometry reference
• GIA Report Check — verifying stone documentation

Next step: Send your brief and we will return a CAD model with dimensions, minimum thickness, setting height and estimated weight in writing, plus front, side and three-quarter views, and hold production until the revision is approved. Custom, OEM and private-label programmes are all available. Contact vinico@zkzdiamonds.com or WhatsApp +86 135 3037 8229.

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Part of our custom jewelry guide.