Abstract: A method and apparatus is provided for crushing a portion of a corrugated plate in a selected area of the corrugations without blocking the grooves. In accordance with the method teeth are inserted into grooves on opposite sides of the corrugated plate and the corrugation ridges associated with such grooves are, axially adjacent such insertion, crushed to a predetermined thickness. The teeth are then withdrawn, the corrugated plate is indexed a desired number of ridges/grooves and the die members are again engaged with the opposite sides of the plate. The apparatus for crushing a plate includes a frame for supporting the plate, a feed apparatus for moving the plate at the desired time in the desired direction, and a forming apparatus for crushing plate ridges in a zone and obstructing, in a transition zone between the crushed ridges and the uncrushed ridges, ridge transverse movement into adjacent grooves.