Reference

Data Sources & Methodology

BendMath ships shop-typical starting values for material constants, formula coefficients, and reference tables. They are screening estimates for planning. Verify with material certificates, tooling-supplier charts, machine ratings, manufacturer documentation, and applicable standards before production.

This page documents what each number on the site is, where it comes from in the codebase, and what to cross-check it against. Use it whenever a calculator result, lookup row, or material default is about to drive a real decision.

Material defaults

Per-material constants used in the calculators

Material	Default K-factor	Min radius factor	Press-brake multiplier	Tensile (psi)	Yield (psi)
5052-H32 aluminum	0.380	1T	0.5×	33,000	28,000
6061-T6 aluminum	0.400	3T	0.75×	45,000	40,000
3003-H14 aluminum	0.370	0.75T	0.35×	22,000	21,000
304 stainless	0.430	1.5T	1.5×	75,000	30,000
316 stainless	0.440	1.5T	1.6×	84,000	42,000
mild steel	0.420	1T	1×	60,000	36,000
cold rolled steel	0.420	1T	1.1×	64,000	44,000
galvanized steel	0.420	1.25T	1.05×	62,000	36,000

Source: data/materials.json. Values are common shop starting estimates for air bending. Different mills, tempers, coatings, and grain orientations can shift each value substantially. They are not certified material constants and do not replace a material certificate.

Formula constants

Empirical numbers baked into the calculators

Air-bend tonnage constant: 575
T_ft = (575 × M × t²) / V

Source: lib/calculators/pressBrakeTonnage.ts. The 575 constant is a widely circulated shop rule of thumb for air bending mild steel with thickness and V-die opening in inches and the result in tons per foot. It is not from a single normative standard — manufacturer charts (Amada, Trumpf, Bystronic, etc.) vary. Cross-check tonnage against the press brake's rated capacity and the punch and die tooling load ratings.

V-die starting factor:
V = 6T (t ≤ 1/8")
V = 8T (1/8" < t ≤ 1/2")
V = 10T (t > 1/2")

Source: lib/calculators/vDieOpening.ts. Common shop starting points for air bending mild steel and aluminum. Heavier plate, harder alloys, and high-strength steels often shift the factor up. Verify with the tooling supplier's chart.

Air-bend inside radius:
IR ≈ 0.16 × V

Source: lib/calculators/vDieOpening.ts. Often called the 16% rule for air bending. Actual produced radius depends on punch tip radius, material, and springback.

Minimum flange to clear the die:
Min flange ≈ 0.7 × V

Source: lib/calculators/vDieOpening.ts. Some shops use 0.67×V or 0.75×V instead. Confirm against the die geometry and your shop's own setup tolerance.

Bend allowance:
BA = (π / 180) × A × (r + K × t)

Source: lib/calculators/bendAllowance.ts. Standard bend allowance for the neutral axis with A in degrees (rotation angle) and r, t, K as inside radius, thickness, and K-factor. The angle is the rotation through which the sheet is bent — for a 90° formed flange, A = 90°. If your drawing labels the included angle, A = 180° − included angle.

Bend deduction:
OSSB = tan(A / 2) × (r + t)
BD = 2 × OSSB − BA

Source: lib/calculators/bendDeduction.ts. Standard outside-setback-based bend deduction for bend angles less than 180°. Hemming and acute coined bends need process-specific data instead.

Reference tables