Shredders have found a widespread application for the comminution of scrap and waste. They can be classified according to their design into those with horizontally and those with vertically mounted rotors. The comminution of plate-shaped (sheet-like) metal pieces in such devices can be divided into four successive phases, which are explained below. Then, investigations with two small-scale shredders, one with a vertically mounted rotor one with a horizontally mounted rotor, are described. The influence of the properties of the feed (e.g., thickness of the feed metal sheets), the influence of the process parameters (e.g., circumferential speed) and the influence of design parameters are shown. In respect of their use of energy both types of shredders are equal. The results of the experiments can be applied for the scale-up of shredders.