Abstract: The impact tool is provided with a piston (15) oscillating within a cylinder (10). For selecting, with which piston impact surface the piston (15) impacts on the head (7) of a tool holder (2) and accordingly for the selection whether the impact tool generates forward or rearward strikes, respectively, the cylinder (10) is displaced pneumatically between two positions. The displacement occurs depending on the position of a switch (21). This changing of the impact direction is simple and makes it possible to fix the tool holder in the housing (1) making the impact tool sturdy.

Abstract: A piston is oscillating periodically within a cylinder, propelled by compressed air. At at least one of its end positions, the piston generates a stroke that acts on a working tool, e.g. a rasp. The sizes of the piston surfaces acted upon by the compressed air and the capacities at the cylinder volumes limited by the piston are dimensioned such that the impact momentum of the piston at both end positions is essentially the same. In case of a bone rasp working tool this equal momentum of the stroke advancing the rasp into the bone and the stroke loosening the tool by retracting it, leads to an optimum working of the bone and as little stress as possible on the patient.