How to Prepare Your STL File for Jewelry Casting

A watertight (manifold) mesh means every edge is shared by exactly two faces, with no holes, gaps, or inverted normals. This is the single most important requirement for casting — if your mesh isn't watertight, the casting house can't calculate volume, and the mold will have defects.

How to check: In Rhino, run MeshRepair. In Blender, select your mesh and go to 3D Print Toolbox → Check All. In ZBrush, use the DynaMesh function to close holes. Our upload tool checks watertightness automatically and will flag issues before you get a quote.

Common fixes: Close open edges, delete internal faces, merge vertices at the same position (weld tolerance of 0.001mm works for jewelry), and recalculate normals to face outward.

Lost-wax casting involves pouring molten metal into a plaster mold. If your walls are too thin, the metal won't flow properly and the piece will be incomplete or fragile. For sterling silver, aim for 0.8mm minimum. For gold (denser and heavier), 0.6mm is usually safe.

Prong tips, filigree details, and ring shanks are the usual problem areas. If a section looks delicate on screen, it'll be even more delicate in metal. Thicken anything under 0.6mm — it's not worth the casting risk.

Pro tip: For pieces with pavé settings or thin bezels, model the stone seats slightly thicker than you think you need. The polishing step removes 0.05–0.1mm of material.

STL files don't carry unit information — they're just numbers. If you modeled in inches but the casting house reads in millimeters, your ring will be 25.4x too large (or too small). Always export in millimeters.

In Rhino: File → Export Selected → STL, then confirm your units are set to millimeters. In Blender: File → Export → STL, set Scale to 1.0 if your scene units are mm. In Fusion 360: Right-click the body → Save as STL, units default to mm.

Quick sanity check: A US size 7 ring has an inner diameter of about 17.3mm. If your exported file shows the ring at 17.3 units across, you're good. If it shows 0.68 (inches), re-export in mm.

STL files are triangle meshes. Too few triangles and your curves look faceted. Too many and the file becomes unnecessarily large. For jewelry, aim for 50,000 to 500,000 triangles. Most ring models land around 100k–200k.

When exporting from Rhino or Fusion 360, use the "Fine" or "High" mesh quality preset. From ZBrush, decimate to about 200k polys — the wax printer resolution is 16 microns, so ultra-high poly counts don't improve the final piece.

Our upload limit is 50MB. If your file is larger than that, run a decimation pass. If you're using Blender, the Decimate modifier with a ratio of 0.5 usually preserves all visible detail while cutting file size in half.

STL files come in two flavors: binary and ASCII. Binary files are 5–10x smaller for the same geometry. Always export as binary STL — it uploads faster and there's zero quality difference.

In Rhino: when the STL export dialog appears, select "Binary" in the File type dropdown. In Blender: ASCII is off by default, so just export normally. In Fusion 360: binary is the default.

We accept both formats, but binary uploads are near-instant while a large ASCII file can take significantly longer to parse.

If you're used to FDM 3D printing, you might be tempted to add tree supports or rafts to your model. Don't. Lost-wax casting has a completely different support strategy — the sprue (the channel where metal enters the mold) is placed by the caster based on the piece's geometry and metal flow characteristics.

Export your piece as a clean, support-free model. If your design has overhangs or hollow sections, just note that in the order — we'll handle the sprue placement and any internal support structures needed for the investment process.

✓ Mesh is watertight (no holes, gaps, or inverted normals) ✓ Minimum wall thickness: 0.6mm (0.8mm for silver) ✓ Exported in millimeters ✓ Triangle count: 50k–500k (check file isn't over 50MB) ✓ Binary STL format ✓ No supports, rafts, or sprues added ✓ All details you want cast are part of the mesh (not separate floating geometry)