Wrong flat length? Check bend angle and dimension conventions

Why a 90-degree test can hide a mistake

At a right angle, the included angle and angle turned from flat are both 90°. In the simple single-bend section used here, included angle α and turned angle θ satisfy θ = 180° − α. Sketch the inside angle and the turning direction before copying a drawing dimension.

Tool terminology varies. Check the current angle definition when using SheetMetal Master or any calculator instead of assuming the inputs are interchangeable.

An included angle of 120 degrees

Assume α = 120°, so θ = 60°; outside A = 60, B = 40, thickness T = 2, formed inside R = 3 mm, and illustrative K = 0.4.

Entering 120° as the turned angle changes both BA and SB. Correcting only one term cannot fix that mistake. These are teaching assumptions, not production settings.

Check four inputs in order

1. Angle: determine whether the tool expects turning angle, included angle, or another convention.
2. Radius: this model uses the formed inside radius, not the outside radius or automatically the nominal punch radius.
3. Dimensions: A and B extend to the virtual sharp. Straight tangent lengths require a different expression.
4. Units: use mm for all lengths, and degrees or radians as required by the calculation.

Keep reference examples

Retain a 90-degree and a non-90-degree teaching example to check a new tool or changed settings. Our calculator explicitly uses angle turned from flat; comparing its result with hand arithmetic helps identify input errors. Keep separate measured production coupons to validate actual material and process conditions.

Scope and references

The model excludes hems, flattening operations, variable thickness, and interacting bend regions. For equations with angular conditions see Inventor unfold equations; for neutral-axis parameters see Fusion sheet metal rules.