Abstract: A sheet bending machine wherein a sheet of metal is fixed between a clamping beam and a lower beam mounted with interchangeable folding rails and wherein the bending is performed by a bending beam being swung against the projecting part of the sheet metal. The interchangeable folding rails have markings, for example, protrusions or recesses on the rear edge which cooperate with a set of members for establishment of a steering code which determines the maximum permissible bending angle for the folding rail. The code may be in the nature of a series of contacts which are opened or closed, dependent on the folding rail being used, having a recess opposite them or not. The state of the contacts may, for example, be sensed by a cam disc which curves synchronically with the swing movement of the bending beam and successively opens the contacts which are connected in parallel above them, so that a current circuit is switched when both corresponding pair of contacts are opened.