COVO KNOWLEDGE
Press Brake Bend Development: Flat Length, Deduction and Hem Dimensions
Published: 2026-08-02
Learn how A and B leg dimensions, sheet thickness, bend deduction, press-line position and hem allowances connect before a press brake job reaches production.
A flat blank is the starting point for every accurate press brake part. This COVO guide explains how to connect finished leg dimensions, sheet thickness, bend deduction, press-line position and hem dimensions before the first cycle. The training pages behind this article use a simple A and B section to explain pressed-edge development. We have redrawn the technical diagrams in English and kept the original calculation relationships visible. Use the formulas as documented starting points, then verify them with the actual punch, die, material and first piece. English redraw of the supplied development example: A and B legs, 2.0 mm sheet thickness, 0.4t deduction and press-line references. What is press brake bend development? Press brake bend development is the process of converting the required formed dimensions into the flat length that must be cut before bending. The calculation must account for the material consumed or released in the bend region. If the blank is too long, the finished legs can exceed the drawing. If it is too short, the part may not reach the required flange or hem dimension. In the examples, A and B represent the straight leg dimensions of a bent section, while t is the sheet thickness. The correct relationship also depends on the drawing datum: inside dimension, outside dimension, bend line, press line or controller coordinate. The 0.4t starting convention for a pressed edge The first training example expresses the developed length as: Developed length = A + B - 0.4t Deduction = 0.4 × sheet thickness For a sheet thickness of 2.0 mm, the illustrated deduction is 0.8 mm. The same convention places the press-line references at approximately A - 0.2t and B - 0.2t . These values make the drawing logic easy to communicate, but the factor 0.4 is an empirical starting value rather than a universal constant. Material strength, actual thickness, inside radius, die opening, punch nose, hemming method and machine condition can move the result. When the part is critical, cut a controlled test blank, make the first bend, measure the released part and update the approved setup value. An alternative bend compensation expression The next training page presents the same development problem with a different deduction symbol: Developed length = A + B - gamma gamma = 2t - BA90 In this training convention, gamma is the press-brake bend compensation. En
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