fed from the outside during the course of the cutting process the same are gradually pressed toward the inside in radial direction by means of the openings of the channel 3 formed between adjacent knives 4 1 until the same are cut by the blades 5 2 in the cutting surface 8 of the second knife group of the knives 4 2 the height offset of the knives 4 1 and 4 2 of both groups has the advantage that the intermediate spaces between the knives 4 1 are greater such that the fiber sections experience only little friction in particular the short fiber sections created by the second cut can be better discharged due to the free space behind the knife 4 1 of the first knife group for this purpose the cutting surfaces 7 and 8 may be arranged such that the knives 4 1 and 4 2 partially overlap each other so that the height offset between the knives 4 1 and 4 2 is smaller than a depth of the knives 4 1 of the first group however as an alternative it is also possible to embody the height offset at the same depth of the knives 4 1 so that the blades 5 2 of the knives 4 2 are arranged at a smaller or equal diameter as the rear of the outer knives 4 1 in the example embodiment according to fig1 the height offset is embodied smaller between the knives 4 1 and 4 2 than half of the depth of the knives 4 1 of the first knife group the size of the height offset resulting between the cutting plane 7 and 8 depends on the.