Abstract: A variable-diameter knife roll is provided with a knife extending parallel to the axis of the roll placed generally radially on a diametral plane, such knife being mounted on a knife carrier able to be adjusted radially outwardly and inwardly. In order to be able to rapidly and simply set the knife roll to suit different formats the knife carrier is articulatingly connected with the joints connecting the two links of two expanding grilles or with respectively one of the arms extending past such joints, of one of the links of the two expanding grilles. Respectively one inner joint of a link of one of the two expanding grilles is arranged fixedly on a knife roller shaft and the respectively other inner joint of the other link is arranged for adjustment in the axial direction on or in the knife roll shaft.