A designer emails a CAD file, the foundry opens it, and the file comes back with three revisions: wall thickness 0.6 mm, minimum band width 1.2 mm, and a fillet where the shank meets the head. The designer is annoyed. The foundry is not being difficult; the file was drawn for rendering, not for metal. Export settings decide whether a pretty model becomes a castable ring, and most of the revisions are the same five settings repeated across every file we receive.

Wall thickness, minimum feature size, and the metric ruler

For a lost-wax silver or gold casting, the minimum wall thickness the shop can reliably burn out and cast is 0.7 mm in sterling and 0.8 mm in 14K yellow gold. Delicate lace below 0.5 mm prints on wax but snaps on the tree. The minimum band width on a comfort-fit ring is 1.4 mm; below that, the ring bends on the customer's hand. Set your CAD units to millimeters before you export, and confirm the unit in the export dialog; files exported as inches and read as millimeters arrive 25.4 times too large, which wastes a print and a tree. The karat reference on Wikipedia explains why gold alloys shrink differently than sterling, which sets the shrink-compensation factor below.

Shrink compensation and export tolerance

Wax prints shrink about 2%, the investment expands roughly 1.5% during burnout, and the metal itself shrinks another 1.8 to 2.5% on cooling. Net result: the CAD file should be scaled up 1.03 to 1.05x before printing, depending on alloy. Most modern casting CAD packages bake this into the export, but if you are sending a neutral STL, scale it yourself and tell the foundry which factor you used. Export tolerance (the chord deviation on curved surfaces) should be set to 0.01 mm for jewelry, not the 0.1 mm default. A coarse tolerance puts visible faceting on a round band after polishing.

STL vs OBJ vs 3MF: what the foundry actually wants

We accept STL, 3MF, and Rhino native files. STL is the lowest common denominator but carries no units; 3MF keeps units and color separation; native Rhino files let us edit a fillet on the spot. For complex pave models, send the native file; the foundry will re-cut seats that are too shallow instead of asking you to export again. Our DFM notes on CAD file factory requirements list the full checklist, and factory default tolerances cover what we apply automatically. If your design relies on moissanite girdle fitting, leave the seat diameter 0.05 mm under nominal; the setter will open it by hand, and a seat that is too big cannot be repaired.

File naming, revision, and what to send with the quote

Name files as designname_v03_final.stl. Send a rendered front-and-side image alongside the file, the target alloy, the target ring size, and the target stone sizes. A foundry that has to guess the stone size will leave seats for a 6.5mm round when your customer has a 7mm stone. We also ask for the expected weight range; if your CAD says 4.2 g and our simulation says 5.8 g, the difference is wall thickness and we want to flag it before printing, not after the tree. One more export detail: never merge the stone into the ring model when you send the STL. Send the ring and the stone as separate files, or leave the seat as a void, because the foundry needs to open the seat slightly by hand after casting and a fused stone makes that impossible. For pavé work, send the native file with the stone positions on a separate layer so we can re-cut any seat that prints undersized.

FAQ: Jewelry CAD export settings for casting

What wall thickness should I design to?

0.8 mm minimum in 14K gold, 0.7 mm in sterling. Delicate features can drop to 0.6 mm but must be supported by a thicker bar behind them.

Should I scale the file before sending STL?

Only if your CAD package does not apply shrink compensation. Use 1.03x for sterling, 1.04x for 14K yellow, 1.05x for platinum.

What STL tolerance do you recommend?

0.01 mm chord deviation. The 0.1 mm default leaves faceting on round bands.

Can I send a render instead of a CAD file?

For quoting, yes. For production, we need the model. We can reverse-engineer a render but the cost and lead time add about a week.

Send your CAD, STL, or reference render to our DFM desk. We will run the wall-thickness, fillet, and shrink-comp check, return a marked-up revision list within 48 hours, and quote the tree as part of your custom manufacturing timeline. No charge for the first revision; the file that prints clean is the file we want to ship. For custom manufactured orders, send the native file, a front-and-side render, the target alloy, the ring size, and the stone sizes in one zip, and we will come back with a castable revision within two working days.

Frequently Asked Questions

How do I verify a factory before placing a bulk order?

Request a production video, business license, export records and a paid sample run. A factory that accepts a 50-piece test order is usually a real manufacturer.

What payment terms do you offer?

30% T/T deposit with the balance against the bill of lading. This protects both sides on first orders and can move to net terms after a track record.

What is your normal reject rate?

3–5% under 10x loupe inspection for cast and set pieces. Defective units are replaced free in the next shipment.

Where is the factory located?

Wuzhou, Guangxi, China—the core lab-grown and moissanite manufacturing cluster. Shipments go via Guangzhou or Shenzhen ports.