Hammer drill

In a hammer drill comprising a tool, and a motor-driven striking mechanism including an axially reciprocable actuating member driven by the motor, said actuating member being a main piston having an axis, and a striker actuated by said actuating member via an air cushion for movements towards and backwards from said tool to transmit impact energy to said tool, the improvement comprising the air cushion composed of two partial air cushions which are formed by two air chambers positioned one after another in the direction of movement of said striker and having changeable volumes, said striking mechanism further including an intermediate piston movable in the direction of the axis of said main piston, and wall means, said intermediate piston having at least one piston rod, said wall means being formed with at least one bore, said piston rod being positioned and slidingly guided in said bore, said striking mechanism being operative so that during the backwards movement of said striker only one of said partial air cushions acts on said striker and during the movement of the striker towards said tool both air cushions act on said striker.