the housing and at its opposite end pivotably connected to a linkage 16 leading to the propelling member 13 the propelling member itself comprises a support plate 17 substantially horizontally extending and having a plurality of plates 18 in parallel relationship to each other so as to be able to move each plate 18 into the spacings between the parallel cutting strips 8 the propelling member 13 is movable in the direction of the arrow p1 upward and downward respectively which will be explained in more detail with reference to fig3 the lower position is indicated by broken line 19 in fig2 from the lower position a guiding member 20 leads to the lower edge of the feed in opening 3 the feed in opening is closed by means of a slide plate 4 having a handle the lower edge 21 of the slide plate actuates a t like spring loaded levermember 22 adapted to set a switch 23 the plate 4 is locked by a locking means 43 fig3 against casual opening parallel to the guiding member 20 a protecting plate 24 having a upstanding flange 25 is arranged on the level of the upper edge of the feed in opening 3 in the flange 25 a grid like sensing member 26 is pivotably mounted which sensing member is adapted to set a switch located on the plate 24 the lever arm 12 is loaded permanently in the upwards direction by a tensioning spring 28 supported in the housing 1 parallel to the spring a damping member 29 like a hydraulic cylinder is arranged at.