Bend radius is one of the first things a fabricator checks when they open a sheet-metal package—and one of the most common sources of silent rework when CAD defaults do not match shop reality.
Why radius matters more than the bend line
Inside bend radius drives tooling selection, springback compensation, and whether a part can be formed in one hit or needs multiple operations. A radius that is too tight for the material thickness often forces custom tooling, secondary ops, or a no-quote until the design changes.
The thickness relationship
As a starting point, many shops expect inside bend radius at or above one times material thickness for common steels and aluminums—but that is a floor, not a universal rule. Higher-strength alloys, thick plate, and long flanges may need larger radii to avoid cracking or distortion. Lock your buy-to thickness before you lock bend tables.
Grain direction and brake strategy
Bending across versus with grain changes how much a flange can tolerate before it splits. If your part has cosmetic faces or tight tolerances on hole patterns relative to bends, call out grain direction or accept that the shop will orient nests for yield—not always for your ideal cosmetic outcome.
K-factor and flat pattern trust
Radius choices feed directly into flat-pattern accuracy. When radius, thickness, or bend allowance assumptions drift between design and shop, hole-to-bend relationships miss—and assembly fights you on the floor. Align on a single bend deduction strategy with your target vendor before you freeze bracket families.
When to loosen versus tighten
Tight radius on a hidden bracket may be fine to relax for cost. Tight radius on a visible enclosure lip may be worth paying for if cosmetics matter. Document which bends are function-critical versus appearance-critical so DFM reviews prioritize the right fights.
Red flags fabricators see in CAD
- Default 0.5 mm radii on 0.125 in stock
- Mixed bend tables within one product family
- Bends so close to holes that distortion is inevitable
- "Form up" notes without sequence or tooling context
Need a second set of eyes before your next quote cycle? We offer DFM audits with bend strategy, tolerance, and drawing clarity called out in actionable terms.