Abstract: An apparatus for producing shear deformation in a work piece, the apparatus comprising: a processing channel through which the work piece passes, the processing channel including first and second channel sections which intersect at an angle to each other; a plurality of drive members configured to engage sides of the work piece to drive it through the processing channel so that the work piece passes from the first channel section to the second channel section to produce shear deformation in the work piece; and a drive surface disposed at an intersection of the first and second channel sections, the drive surface being configured to engage the work piece and advance it through the intersection, wherein opposing sides of the first channel section are defined by a pair of die faces relative to which the drive members are rotatably fixed, the separation of the die faces being variable in response to thickness variations of the work piece to maintain drive of the work piece through the processing channel.