1 mm 304 stainless steel bend allowance and bend deduction
At a 90° bend with an inside radius of one thickness (1.00 mm / 0.0394 in) and K = 0.45, 1 mm 304 stainless steel (1 mm / 0.0394 in) has a bend allowance of 2.28 mm (0.0897 in) and a bend deduction of 1.72 mm (0.0678 in).
| Bend angle | Included angle | BA (mm) | BD (mm) | BA (in) | BD (in) |
|---|---|---|---|---|---|
| 30° | 150° | 0.76 | 0.31 | 0.0299 | 0.0123 |
| 45° | 135° | 1.14 | 0.52 | 0.0448 | 0.0204 |
| 60° | 120° | 1.52 | 0.79 | 0.0598 | 0.0311 |
| 90° | 90° | 2.28 | 1.72 | 0.0897 | 0.0678 |
| 120° | 60° | 3.04 | 3.89 | 0.1196 | 0.1532 |
| 135° | 45° | 3.42 | 6.24 | 0.1345 | 0.2457 |
| Inside radius | R / T | K-factor | BA (mm) | BD (mm) | BA (in) | BD (in) |
|---|---|---|---|---|---|---|
| 0.50 mm | 0.5 | 0.40 | 1.41 | 1.59 | 0.0557 | 0.0625 |
| 1.00 mm | 1 | 0.45 | 2.28 | 1.72 | 0.0897 | 0.0678 |
| 1.50 mm | 1.5 | 0.45 | 3.06 | 1.94 | 0.1206 | 0.0763 |
| 2.00 mm | 2 | 0.45 | 3.85 | 2.15 | 0.1515 | 0.0847 |
| 3.00 mm | 3 | 0.45 | 5.42 | 2.58 | 0.2134 | 0.1016 |
Practical notes
The angle in these formulas is the bend angle — how far the flange turns away from flat. The included angle between the two flanges is 180° minus the bend angle, so a 90° bend is also 90° included, but a 135° bend leaves a 45° included angle.
K-factor values here come from a generic air-bending table that depends on R/T (about 0.40 below R = T, 0.45 from T to 3T, 0.50 above 3T for 304 stainless steel). They are approximations: tooling, die width, grain and temper all shift the neutral axis. Bend a test strip, measure the flanges and back-calculate K before cutting a production run.
A V-die opening of about 8 × T (8.00 mm / 0.3150 in) is the usual starting point. In air bending the inside radius forms at roughly 20–22% of the die opening for 304 stainless steel, so the radius you actually get depends on the die more than the punch — recompute with that radius if it differs from the R = T used above.
Springback for 304 stainless steel at modest radii is typically about 2–4°, increasing as R/T grows; overbend to compensate. It changes the angle, not the bend allowance calculation.
304 stainless needs roughly 1.5–2 times the press force of mild steel of the same thickness and about 1 × T is a common minimum for annealed 304; it work-hardens quickly, so avoid re-bending. Use protective film or urethane tooling if the finish matters.
FAQ
What is the bend deduction for 1 mm 304 stainless steel at 90°?
With R = T (1.00 mm / 0.0394 in) and K = 0.45, the bend deduction is 1.72 mm (0.0678 in). For a part with two 50 mm flanges measured to the outside, the flat blank is 50 mm + 50 mm − 1.72 mm = 98.28 mm.
What K-factor should I use for 1 mm 304 stainless steel?
For air bending 304 stainless steel at R = T, a K-factor of about 0.45 is a typical starting value; below R = T it drops to about 0.40, and above 3 × T it approaches 0.50. Real values depend on tooling and material lot, so confirm with a test bend.
Why does 304 stainless steel need more overbend than mild steel?
304 stainless has a higher yield strength and work-hardens as it bends, so it springs back more — typically about 2–4° at modest radii versus about 0.5–2° for mild steel. The bend allowance is unchanged; only the brake setting differs.
Is the angle in the bend allowance formula the bend angle or the included angle?
It is the bend angle, the amount the flange is turned from flat. If your drawing gives the included angle between flanges, use 180° minus that value: a 45° included angle is a 135° bend.
Sources: Bend allowance formula BA = A·(π/180)·(R + K·T); bend deduction BD = 2·tan(A/2)·(R + T) − BA (Machinery's Handbook, sheet metal bending) · Generic air-bending K-factor table by R/T (approximate)
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