The render is not the part
A polished CAD render is a sales tool, not a manufacturing plan. The moment a custom ring leaves the designer's screen and enters the casting pipeline, it must survive physical laws the render never modeled: metal feed, solidification, burnout shrinkage, and residual stress. Most "the CAD looked fine" failures happen because the design was treated as finished at the render stage rather than handed off to the caster early enough to rework geometry. The custom workflow runs CAD, print, burnout, and casting as one conversation, not a relay race.
CAD built for casting
A casting-ready CAD file does not just look right - it has wall thickness the alloy can fill, generous fillets where sections meet, and no razor-thin edges the resin printer cannot reproduce. Rings with undercuts, internal tunnels, or extremely fine prongs are flagged before printing, because the caster will add gates and vents that must land on clean metal. The designer also models in a shrink allowance: gold and silver shrink during solidification, so the pattern is printed slightly larger than the finished dimension. Skip the allowance and every ring comes up a half-size small.
Supports and gates: the caster's markup
Before printing, the caster adds supports and gates - the channels through which molten metal enters the pattern and through which air escapes. Gating is where casting skill lives: a ring with a poorly placed gate arrives with porosity at the high-tension point (often the shank shoulder), and that is a structural fault, not a cosmetic one. Good gating feeds the heaviest section first, lets thin sections fill last, and positions the gate where it will be hidden or ground away cleanly. This markup happens after CAD and before print, which is why the caster reviews the file, not just the designer.
Resin printing and support removal
The approved file prints as a high-detail resin (or milled wax) pattern. Modern resin printers reproduce prong tips, engraving depth, and milgrain close to production quality, but supports must be removed carefully - nicking a thin prong here is repaired later by hand. The printed pattern is then inspected against the CAD: measured for size, checked for missing sections, and weighed as a sanity check. A pattern that prints with a missing prong or a deformed basket goes back to reprint, never to the flask. Printing failures cost hours; casting failures cost a whole flask.
Investment, burnout, and casting
The pattern is mounted on a sprue, invested in a plaster-like ceramic flask, and put through a burnout cycle that vaporizes the resin or wax completely, leaving a hollow mold exactly the shape of the part. Molten alloy is then introduced, usually under centrifugal or vacuum pressure, to fill every detail. Temperature control across this cycle decides casting quality: too hot and the grain coarsens; too cold and metal freezes before filling fine prongs. The result, once the flask is broken and the sprue removed, is a rough casting - skin-textured, gated, and nowhere near finished. It is a blank for the bench, not a product.
Cleanup is where CAD becomes craft
From here the ring moves to fitting, sizing, setting, and the multi-stage polish. The cast skin is removed, the gate ground flush, the shank rounded, and only then do stones go in. A CAD-perfect design can still end up looking off if cleanup removes too much metal at a delicate spot, which is why experienced designers leave extra material where the bench will work. The hand-off loop closes when the finished piece is measured against the original CAD dimensions - size, weight, and stone seat - and the difference feeds back into the next design.
The most common hand-off failures
Three failures recur on custom jobs. The first is a CAD that looks thin on screen but the caster cannot feed: a ring with a 0.4mm shank on the render, which casts as a porous, fragile blank that breaks at cleanup. The fix is agreed minimum wall thickness before print, not after. The second is a shrink allowance forgotten, which comes back as a ring that measures a half-size small on QC and needs rework or re-cast. The third is a stone seat sized to the catalog spec rather than the actual stone - if the client's heirloom diamond measures 6.3mm but the CAD was built for a 6.5mm head, the stone rattles or the prong has to be stretched to reach it. Good shops measure the physical stone, or a caliper sample, before locking the file.
None of these are design-flaw emergencies if caught at print or cast; they become emergencies only when the first time the customer sees the part is the finished, set, polished piece, when rework means resetting stones and re-finishing from scratch. That is why the checkpoint photos exist.
What custom clients should ask
Commissioning a custom piece? Ask whether the caster reviews the CAD before printing, whether shrink allowance is built in, and whether you see photos of the printed pattern and the raw casting before finishing. Those two checkpoints - print and cast - are where problems are cheap to fix. A shop that only sends you the final photo is hiding the hand-offs that actually determine quality. See our custom jewelry workflow for how we stage CAD-to-casting approvals.
For third-party reference, the Wikipedia article on moissanite details moissanite’s discovery, optical properties and use in jewellery.
Frequently Asked Questions
What ring sizes can you supply in bulk?
US sizes 5–12 including half sizes. Send a size breakdown with your order and we cast to that curve; comfort-fit inner bands reduce resize requests.
Can I order a mixed size run instead of one size?
Yes. Mixed runs are standard for wholesale: specify quantity per size and we pack and label by size at no extra labor cost.
What is the MOQ for custom ring designs?
50 pieces per design for existing molds; 100–300 pieces when a new mold or CAD model is required.
How should I price rings for retail margin?
Most partners use a 3–4x markup on FOB cost for sterling and 2.5–3x for moissanite solos, which keeps landed cost under 30% of retail.
