What is the difference between Bend Allowance (BA) and Bend Deduction (BD)?

Bend Allowance (BA) is the developed arc length of the neutral axis around the bend. Bend Deduction (BD) is the total amount subtracted from the sum of outside flange dimensions (L1 + L2) to yield the flat blank pattern length (L_blank = L1 + L2 - BD). BD is related to outside setback by BD = 2·OSSB - BA.

How is the K-factor defined?

The K-factor represents the position of the neutral axis (the plane that experiences zero compression or elongation) as a fraction of material thickness: K = t_n / T. It typically ranges from 0.30 for sharp coin bends up to 0.50 for large-radius radius bends.

What is the DIN 6935 empirical K-factor formula?

Under German standard DIN 6935, the empirical K-factor is calculated as K = 0.65 + 0.5·log10(R/T), clamped between 0.25 and 0.50 based on the inside radius to thickness ratio.

Fabrication & Sheet Metal

DIN 6935 / Machinery's Handbook

PRO Suite

Sheet Metal Bend Allowance & K-Factor PRO Calculator

Calculate exact flat blank pattern lengths, Bend Allowance (BA), Bend Deduction (BD), Outside Setback (OSSB), and neutral axis K-factors per DIN 6935 and Machinery's Handbook.

Outer fiber tensile elongation (ε = 33.3%) exceeds material fracture limit (28%). Severe risk of orange-peel microcracking along the bend line.

Flat Pattern Blank & Bend Geometry Audit

l-bend (90°)

Flat Blank Length (L)96.40mm

Bend Allowance (BA)4.398mm arc

Bend Deduction (BD)3.602mm

Outside Setback (OSSB)4.000 mm

Inside Setback (ISSB)2.000 mm

Neutral Axis Offset (t_n)0.800 mmK = 0.400

K-Factor & Outer Fiber Tensile Strain

CRACKING RISK

Applied K-Factor: 0.400DIN 6935 Prediction: 0.500

K = 0.20 (Sharp/Thinning)Neutral Axis Ratio (t_n/T)K = 0.50 (Theoretical Midplane)

Outer Tensile Strain: 33.3%Mild Steel / CR4 (Low Carbon) Limit: 28%

ε = 0%R/T = 1.00 (Min R = 2.00 mm)ε = 50%

Bend Angle Sensitivity: BD & Blank Length

Blank Length (L)

Bend Deduction (BD)

Hover over points to inspect how Bend Deduction (BD) scales and modifies flat pattern blank dimensions across acute and obtuse angles.

Calculation Summary

Input Parameters

Sheet Thickness (T)	2mm
Inside Radius (R)	2mm
Bend Angle (A)	90°
Material	Mild Steel / CR4 (Low Carbon)
K-Factor (t_n/T)	0.400
R/T Ratio	1.00

Calculated Results

Flat Blank Length (L)	96.398mm KEY
Bend Allowance (BA)	4.398mm KEY
Bend Deduction (BD)	3.602mm
Outside Setback (OSSB)	4.000mm
Neutral Axis Shift (t_n)	0.800mm
Outer Surface Strain	33.3% KEY

Safety Notes

Neutral axis developed per DIN 6935 / Machinery's Handbook. Outer strain is 33.3% against material fracture limit of 28%.

Mathematical Models & Equations

Bend Allowance (BA)

BA = \frac{\pi}{180} \cdot A \cdot (R + K \cdot T)

Outside Setback (OSSB)

OSSB = (R + T) \cdot \tan\left(\frac{A}{2}\right)

Inside Setback (ISSB)

ISSB = R \cdot \tan\left(\frac{A}{2}\right)

Bend Deduction (BD)

BD = 2 \cdot OSSB - BA

Flat Blank Length (L-Bend)

L_{blank} = L_1 + L_2 - BD = (L_1 - OSSB) + BA + (L_2 - OSSB)

DIN 6935 Empirical K-Factor

K = 0.65 + 0.5 \cdot \log_{10}\left(\frac{R}{T}\right) \quad [0.25 \le K \le 0.50]

Outer Surface Strain (ε)

\epsilon_{outer} = \frac{1}{2(R/T) + 1} \cdot 100\%

Verification Calculation Log

1Neutral Axis Location: Sheet Thickness T = 2 mm, K-Factor K = 0.400 → Neutral Axis Offset t_n = K · T = 0.800 mm from inside bend surface (Neutral Radius R_n = 2.800 mm).
2Bend Allowance (BA): BA = (π/180) · 90° · (2 + 0.400 · 2) = 4.398 mm (Developed arc length of neutral axis).
3Outside & Inside Setback: OSSB = (2 + 2) · tan(90/2) = 4.000 mm (ISSB = 2.000 mm).
4Bend Deduction (BD): BD = 2 · OSSB - BA = 2 · 4.000 - 4.398 = 3.602 mm.
5Flat Blank Pattern (L-BEND Profile): Total Blank Length L = 96.398 mm (Flange 1 flat = 46.000 mm, Flange 2 flat = 46.000 mm).
6Formability & Outer Strain: R/T = 1.00 → Outer Tensile Strain ε = 33.3% (Material Mild Steel / CR4 (Low Carbon) elongation limit = 28%).

Engineering DisclaimerEngineering calculations are provided for preliminary design and educational/reference purposes only. Users must verify all results according to applicable engineering standards, supplier data, manufacturing requirements, and professional engineering judgment.

Sheet Metal Bend Allowance & K-Factor PRO Calculator

Flat Pattern Blank & Bend Geometry Audit

K-Factor & Outer Fiber Tensile Strain

Bend Angle Sensitivity: BD & Blank Length

Calculation Summary

Mathematical Models & Equations

Verification Calculation Log

Sheet Metal Bend Allowance & Flat Blank Report — Calculation Report

Sheet Metal Bend Allowance & Flat Blank Report

Design Inputs

Calculated Results

Related Calculators

Applicable Standards

Related Formulas

Engineering Data

Flat Pattern Blank & Bend Geometry Audit

K-Factor & Outer Fiber Tensile Strain

Bend Angle Sensitivity: BD & Blank Length

Calculation Summary

Mathematical Models & Equations

Verification Calculation Log

Sheet Metal Bend Allowance & Flat Blank Report — Calculation Report

Sheet Metal Bend Allowance & Flat Blank Report

Design Inputs

Calculated Results

Related Calculators

Applicable Standards

Related Formulas

Engineering Data

Flat Blank Length:	96.398 mm
Bend Allowance:	4.398 mm
Bend Deduction:	3.602 mm
Outside Setback:	4.000 mm
Outer Strain:	33.3%