About 85% of the CAD files that hit our trade portal are castable as-is. The remaining 15% share the same handful of mistakes — and those mistakes turn a 24-hour quote into a 48-hour back-and-forth, and a 3-day casting cycle into 4 or 5 days.

This is the checklist for the file you're sending us, written from the CAD bench. Five minutes of pre-flight saves a day in the cycle, every time.

File formats we accept

  • .STL — most common, lossy but adequate for almost everything. Use a high export resolution (deviation ≤ 0.01 mm).
  • .3DM — Rhino native. Best because curves stay as curves, not approximated as triangle meshes.
  • .OBJ — accepted, similar properties to STL.
  • .STP / .IGES — preferred for complex parametric geometry from solid modellers (Solidworks, Fusion 360, Inventor).

If your bureau exports something else, ask us — we can usually translate.

Wall thickness rules

Thickness Verdict
≥ 0.6 mm Casts reliably
0.4–0.6 mm over short spans Castable with care; we may add a vent
< 0.4 mm Flagged for review
Internal pockets, non-vented 1.0 mm minimum
Internal pockets, vented 0.6 mm acceptable

Run a wall-thickness analysis in your CAD software before export. The tools differ (Rhino: ShellThickness analysis; Matrix: Verify; Fusion 360: Section analysis with thickness colour map) but they all surface the same problems.

Sprue placement

If you've placed sprues, we work with your placement. If not, we add them.

Best practice for self-sprueing:

  • Place at the heaviest section of the piece
  • Avoid visible surfaces — sprue scars are real, even after cleanup
  • 2–3 mm sprue diameter for pieces under 5 g; 3–5 mm for larger
  • Add a runner if the mass is distributed across distant points (e.g. a halo with a separate mounting underbasket)

The five common problems

1. Closed pockets / water-traps. Pockets without a vent path. The wax burns out fine, but the metal can't fill them cleanly because the trapped gas has nowhere to go. Symptom: pinholes or incomplete fills in the cast. Solution: add a vent — a small hole or channel that breaks through to a non-visible surface. We can add it for you, but you lose a day.

2. Mating-surface mismatches. For two-part designs (a halo dropping onto a basket, a hidden halo under a centre stone), the contact surfaces need to match within 0.05 mm. Bureaus often miss this because they design each part independently. Solution: union or boolean the parts in the design software, check the contact surface tolerance, then split for casting.

3. Wall thickness below tolerance. Usually shows up at prong tips, claw bases, or filigree details. The designer thickened the visible parts and forgot the back. Solution: run the wall-thickness analysis. The five minutes catches a day's worth of back-and-forth.

4. Sprues at the wrong location. Sprues on a visible surface (the bezel rim, the gallery), sprues meeting the casting at 90° (causing metal turbulence), sprues too thin for the piece's mass. Solution: if you're new to self-sprueing, just leave them off and we'll add them. We've spent more time looking at sprues than most CAD people have.

5. Wrong units or scale. Exported in inches when the model was designed in mm, or accidentally scaled to 200%. We catch most of these in the visual check, but it adds time. Solution: include a reference dimension in your upload comment (e.g. "ring is size 54, internal diameter 17.2 mm").

Tolerances we work to

  • Linear dimensions: ±0.05 mm typical, ±0.10 mm worst case
  • Cast weight vs. CAD-predicted: within 0.05 g for pieces under 10 g, within 0.5% for larger
  • Surface finish: as-cast on setting surfaces (we don't pre-polish those — you do)
  • Wall thickness deviation: within ±0.03 mm where measurable

Tighter tolerances are possible — micro-pavé and signet engraving sometimes need ±0.02 mm. Add a note to the upload if your piece needs that and we'll route it accordingly. There's a small surcharge but no extra days.

What slows down a quote

  • File without dimensions or unit reference (we have to ask before quoting)
  • File with errors needing correction rounds (each round ≈ +1 day)
  • Multi-flask runs without piece count or alloy specification
  • Customer-supplied gold without weight declaration
  • Files in proprietary formats we can't open (rare, but it happens)

What speeds it up:

  • Brief paragraph in the upload describing the piece, intended metal, any tolerances that matter
  • A reference dimension or stated ring size on the file
  • A previous reference job number if you've cast with us before — we apply your conventions automatically

Pre-flight checklist

Before clicking upload, walk through:

  • File in an accepted format (.STL / .3DM / .OBJ / .STP / .IGES)
  • Wall-thickness analysis run, no surfaces below 0.4 mm
  • No closed pockets (or all closed pockets vented)
  • Mating surfaces matched, for multi-part designs
  • Sprues placed — or note "please add sprues"
  • Reference dimension or stated ring size
  • Brief paragraph describing the piece, metal, deadline if any

Five minutes. Saves a day. Every time.

What to do next

By Marie — CAD and design at Antwerp Ateliers. Marie reviews every CAD file that lands in the trade portal and is the person flagging your file's problems before they become tomorrow's problems.