Roll bender

A roll bender is a mechanical jig having three rollers used to bend a metal bar into a circular arc.

If a bar is used, it is assumed to have a uniform cross-section, but not necessarily rectangular, as long as there are no overhanging contours, i.e. positive draft.

The portion of the bar between the rollers will take on the shape of a cubic polynomial, which approximates a circular arc.

During the rolling process, the force applied to the center roller is incrementally increased to gradually bring the arc of the bar to the desired radius.

The amount of spring back depends upon the elastic compliance (inverse of stiffness) of the material relative to its ductility.

Roll bender machine
A schematic showing a typical three roller arrangement
Forming a 7-foot diameter wheel rim with a roll bender
Close up of the roll bender jig