Why Your Finished Piece Is Never Quite the Same Size as Your CAD Model
If you've ever ordered a cast piece and noticed it came out slightly smaller than your original design, you weren't imagining things. Casting shrinkage is one of the most important — and most misunderstood — factors in jewelry manufacturing. For designers, retailers, and independent brands working with a casting house, understanding this phenomenon can save you time, money, and a great deal of frustration.
What Is Casting Shrinkage?
Casting shrinkage refers to the reduction in volume and dimensions that occurs as molten metal cools and solidifies inside a mold. When metal transitions from liquid to solid, its molecular structure compresses, causing the finished piece to be measurably smaller than the wax model or 3D-printed pattern used to create it.
This isn't a defect — it's a predictable physical property of metal. The key is accounting for it before your design ever reaches the casting flask.
Shrinkage Rates by Metal Type
Different alloys shrink at different rates, which is why a one-size-fits-all approach to jewelry CAD design simply doesn't work. Here are approximate volumetric shrinkage rates for common jewelry metals:
- Sterling Silver (925): approximately 4–6% shrinkage
- Yellow Gold (18K): approximately 4–5% shrinkage
- White Gold (18K): approximately 3–5% shrinkage
- Platinum (950): approximately 3–4% shrinkage
- Brass / Bronze: approximately 5–7% shrinkage
These figures can vary depending on alloy composition, flask temperature, injection pressure, and the geometry of the piece itself. A hollow, open design will behave very differently from a dense, solid casting.
How Shrinkage Is Compensated in the CAD Design Phase
Professional jewelry CAD designers — like our team at JewelCAD Design Ltd — compensate for shrinkage by scaling up the digital model before the wax pattern is produced. This is called applying a shrinkage allowance or scale factor.
For example, if you need a ring shank to be exactly 2.0mm wide in the final sterling silver piece, the CAD model may be built at 2.10mm to 2.12mm to account for expected metal contraction. Stone seats, prong dimensions, and ring sizes all require individual consideration.
"Getting shrinkage compensation right at the design stage is far more cost-effective than correcting a finished piece. One accurate CAD file can produce hundreds of consistent castings."
Practical Tips for Working With a Casting Partner
If you're a designer or brand sourcing manufacturing services, here's how to ensure shrinkage doesn't derail your project:
- Always specify your target metal. Share this information before CAD work begins, not after. The alloy determines the scale factor your manufacturer will apply.
- Request a first-article sample. Before placing a bulk order, approve a single cast prototype and physically verify critical dimensions against your spec sheet.
- Provide stone sizes in advance. If your design features set stones, provide exact millimeter dimensions so stone seats can be cut with the correct post-shrinkage tolerance.
- Communicate ring size requirements clearly. Ring sizing must account for shrinkage. Always confirm whether sizes quoted are pre- or post-casting.
- Work with experienced CAD designers. Automated scaling is a starting point, but an experienced designer knows that different sections of the same piece may require different compensation levels.
Why This Matters for Your Brand
Consistency is the foundation of a trustworthy jewelry brand. Customers expect a ring in size 7 to actually be a size 7. They expect stone settings to hold securely and proportions to match what they approved. Poorly managed casting shrinkage leads to costly rework, delayed shipments, and returns that damage your reputation.
At JewelCAD Design Ltd, our Bangkok-based team integrates shrinkage compensation into every project from the first modeling session. We work with sterling silver, gold, platinum, and brass, and we guide clients through the entire process — from initial concept to finished casting — ensuring your vision translates accurately into metal.
Ready to Start Your Next Project?
Whether you're developing your first collection or scaling an established line, understanding the technical realities of casting will make you a smarter, more confident design partner. Reach out to our team to discuss your specifications and let us show you how precision manufacturing starts long before the metal is ever poured.