A stainless fabrication shop needed flat blank dimensions for a simple 3"×2" angle bracket in 16ga 304 stainless (0.0625") with a single 90° bend at 0.125" inside radius. The shop had been using mild steel K-factor (0.38) on their stainless jobs — causing blanks to come out 0.003–0.005" over per bend. Using K=0.34 from the Machinery's Handbook stainless air-bend table, the flat blank came to 4.834". More importantly, the springback estimate of ≈5° on stainless meant they needed to over-bend to 85° — much more than the 2.5° required for mild steel on the same geometry.
Frequently Asked Questions
Why does stainless need a different K-factor than mild steel?
Stainless steel work-hardens more aggressively during bending than mild steel. The increased work-hardening shifts the neutral axis slightly inward (toward the inner radius), giving a lower K-factor (0.34 vs. 0.38 for mild steel). The effect is small per bend — about 0.002" difference on 16ga at 90° — but it matters on multi-bend parts or tight tolerances.
Why does stainless springback so much more than mild steel?
Stainless has a higher yield strength and lower modulus ratio than mild steel — meaning it stores more elastic energy during bending and releases more when the die lifts. 304 stainless springs back 4–7° on a 90° air bend at r/t = 2.0. Mild steel at the same geometry springs back only 2–3°. Always run a test piece on stainless — the springback is sensitive to temper, hardness lot, and tooling clearance.
How much does getting K-factor wrong matter on a single-bend part?
On a single 90° bend in 16ga stainless, using K=0.38 (mild steel) instead of K=0.34 (stainless) gives a flat blank 0.002" longer than correct. That's within tolerances for most brackets. The real cost is on springback — mild steel K with mild steel springback compensation (2.5°) on a stainless part leaves you 2.5° under-bent and you scrap or re-run the bend.
How does IronKit select K-factor automatically?
The K-factor is looked up from the Machinery's Handbook table by material + r/t ratio. 304 stainless at r/t = 2.0 falls in the r/t 1–3 bracket → K = 0.34. You can override K per bend by entering your own measured value from test pieces.