This disclosure relates to a method and apparatus for punching out blanks from sheet materials. The material is laid on a base plate and punch knives are arranged in a pattern upon the material and covered by a pressure plate to form a sandwich assembly which is conveyed through a roller punching machine to force the knives through the material. When the sandwich has passed between two pressure rollers, the pressure plate is returned to its starting position with the aid of one of the rollers which rotate continuously in the same direction. A new sandwich may then be passed between the rollers. In a modification an electromagnetic lifting device is provided comprising a frame on which bar magnets are adjustably mounted so that the punch knives can be removed and replaced without disturbing their original pattern of distribution.