With known trimming shears having a pair of scrap-cutting blades on the discharge side, the moving upper scrap-cutting blade must be moved as closely as possible past the trimmed plate edge in order to push the cutoff edge still hanging on the plate downward against the lower fixed scrap-cutting blade, which requires precise adjustment of the upper scrap-cutting blade. To that end, according to the invention, the distance between the upper scrap-cutting blade (2) or the lower scrap-cutting blade (3) and the trimming blade plane (5) is set prior to trimming in accordance with the thickness of each heavy plate (10) to be trimmed by displacement of the upper scrap-cutting blade (2) and/or the lower scrap-cutting blade (3) in a displacement direction with at least one component transverse to the trimming blade plane (5).