A 3 mm steel plate gets a right-angle (90°) bend. What inside radius and leg length belong to it, and how much flat length do you subtract from the outside dimensions?
The table decides buildability, not the drafter
For every combination of material, plate thickness and bend type, the table gives three dimensions: the supplier's reference resulting inside radius Ri, the minimum supported flange length s according to the supplier diagram and the groove width w of the tooling used. These aren't free CAD choices — they follow from the combination of plate thickness, material and the tooling the supplier actually runs.
Worked example: 3 mm steel, right angle
For 3 mm steel with a right-angle bend, the table gives Ri = 2.75 mm, a groove width w = 16 mm and a minimum leg length s = 12.4 mm. For holes and slots, use the separate check with the correct outside-face/virtual-corner datum, hole size and interruption limits; s is not a centre-distance rule.
From inside radius to flat length
To determine the flat pattern before bending, use the bend allowance BA = (π/2)·(Ri + K·t) — the arc length of the neutral line — and the bend deduction BD = 2·(Ri + t) − BA, how much shorter the flat length is than the sum of the outside dimensions. With Ri = 2.75 mm, t = 3 mm and a rule-of-thumb K = 0.33, that gives BA ≈ 5.87 mm and BD ≈ 5.63 mm. The K-factor is a rule of thumb that varies from 0.3 to 0.5 with material and the Ri/t ratio — this is an estimate, not a table value, and is worth checking against your own press brake for a critical dimension.
Assumptions and applicability limits
The Ri/w/s values are transcribed literally from the 247TailorSteel guidelines and hold for that supplier and tooling — not as a universal standard for every press brake. Some cells don't rise monotonically with plate thickness; for right-angle RVS (stainless), for instance, Ri drops from 11.91 mm at 6 mm to 11.64 mm at 8 mm. That's not a data-entry error but a literal transcription of the source table. Always verify critical dimensions with the actual sheet-metal shop before production.