Abstract: A folding machine has workpiece sensing means including an emitter by which an "outside" corner in the workpiece edge approaching the operating locality of the machine can be sensed, such sensing causing the feed length by which the workpiece is advanced step-by-step through the operating locality to be reduced; this conventionally causes pleating in the folded over edge portion. In addition, delay means is provided by which, after the emitter has been re-covered by the workpiece, the feed length reduction continues for a given number of further feed steps.