Process
Inspection
A wire form is a centerline in space. Measure the interfaces the assembly cares about. Chaining ±0.005 in down every leg is how you reject good parts and ship bad ones.
What to measure
Put datums on the mating part: hole pattern, hook span, clip gap, envelope that has to clear a cover. Those get a fixture or a CMM program. Non-mating bends float at process capability.
After weld or MIG / TIG, inspect the welded state. Form-only numbers will not survive a fillet on a 12 mm frame.
Detail on how to dimension: design for wire forming.
Fixtures, overlays, CMM
- Hard fixture — the default for production 2D and for 3D parts with a few critical spans. Go/no-go. Cheap per piece, honest if the fixture matches the assembly.
- Overlay / optical — 2D forms on a comparator or scan. Fast prove-out. Weak on out-of-plane kick.
- CMM / scan — 3D centerlines, first article, PPAP. Slow. Use it to prove the fixture, not to 100% a 50,000-piece grid.
- Weld checks — peel or pull on a sample coupon for cross-wire; visual and size for fillets.
What changes from 4 to 14 mm
| Diameter | Inch | Inspection |
|---|---|---|
| 4 mm | 0.157 in | Overlay still works on 2D. ±0.5 mm on a short clip is tight; ±0.15 mm on a span is a fixture job. |
| 8 mm | 0.315 in | Fixtures for hole patterns. CMM for 3D first article. |
| 12 mm | 0.472 in | Frames: fixture the interfaces. Do not CMM every radius on a production lot. |
| 14 mm | 0.551 in | Think fabrication tolerances. ±0.5 mm on a 400 mm span is a conversation, not a default. |
First article
A first article on a 3D CNC form is a program, a straightener setting, and a springback guess that got lucky once. Freeze the material spec before you freeze the FA. Changing 304 to “equivalent” 302 without a new article is how a clip stops snapping on.
Send the same files you want production held to: PDF with critical dims, STEP or DXF of the centerline, material cert, finish. A photo is not an FA package.
Default starting tolerances
| Feature | Starting point |
|---|---|
| Linear, non-critical | ±0.015 in / ±0.4 mm |
| Linear, critical, fixtured | ±0.005 in / ±0.13 mm |
| Angle, non-critical | ±2° |
| Angle, critical | ±0.5° to ±1° |
These are starting points for 4–14 mm CNC, not a promise on every alloy and every span. Tighter is a fixture and a conversation.