Sheet Metal Bend Radius Calculator

What Is Minimum Bend Radius?

Minimum bend radius is the tightest radius a material can be bent to without cracking or fracturing on the outside of the bend. It's expressed as a multiple of material thickness — a 1×t radius means the inside radius equals the material thickness.

Going below the minimum causes the outer fiber of the material to exceed its tensile elongation limit, resulting in cracking. Softer materials and lower-strength alloys tolerate tighter radii than hard or high-strength materials.

Why Aluminum 6061 Cracks When You Bend It

6061-T6 (the most common structural aluminum) has very low elongation compared to 5052. It's strong but brittle in bending. The minimum bend radius for 6061-T6 is 4× to 6× the material thickness depending on direction relative to the grain.

Bending across the grain (perpendicular to the rolling direction) requires a larger radius than bending with the grain. When 6061 must be bent tightly, anneal it first or switch to 5052 which is specifically designed for forming.

Springback — Why Your Bend Angle Is Always Wrong

Springback is the elastic recovery that occurs after the bending force is removed. Every material springs back some amount — the punch removes, the part opens up slightly. Springback increases with material strength and decreases with tighter radii.

To compensate, overbend by the springback angle — if the part needs 90° and the material springs back 5°, bend to 85°. Always test a sample piece first and measure the actual springback before running production parts.

Inside Radius vs Outside Radius — Which One Matters?

The inside radius is the standard reference for bend calculations — it's the radius at the compressed side of the bend. The outside radius equals inside radius plus material thickness.

When a drawing calls out a bend radius without specifying inside or outside, assume inside radius. For tooling selection on a press brake, the punch nose radius should match your target inside radius. The die opening determines the actual achieved radius through air forming.

Diagnose Failures & Choose BA vs BD

Finished dims wrong, cracks, springback, or short flanges: Sheet Metal Bending Troubleshooting. Additive vs subtractive flat-pattern method: Bend Allowance vs Bend Deduction — Which to Use.

Related Sheet Metal Tools

• → Press Brake Tonnage Calculator
• → Press Brake Tonnage Guide
• → Bend Allowance Calculator
• → Bend Radius Calculator
• → Sheet Metal Gauge Chart
• → Sheet Metal Bending Troubleshooting
• → Bend Allowance vs Bend Deduction
• → Sheet Metal Bending Guide

Cone & Transition Flat Patterns

For developed cone, frustum, and lobster-back templates (printable PDF), use the Cone / Transition Flat-Pattern Generator, the usage guide, troubleshooting, and seam allowance by joining method.