1,026,256. Percussive tools. ATLAS COPCO A.B. March 1, 1965 [March 6, 1964], No. 8617/65. Heading B4C. A percussive tool comprises a hammer piston 33, 34, 35 driven on a working stroke by combustion gases in a chamber 29 and returned by a pressurized air in a pressure chamber 28, a manually-operable valve 58 being movable between a position in which pressure is built up in the chamber 28 to produce the full impact power of the piston and a further idle position in which the chamber is vented so that the piston does not effect its impact stroke. The compressed air is fed to the pressure chamber 28 by means of a piston 19 movable in a chamber 25 and connected to a piston 17 of an internal combustion engine. The tool bit 43 is mounted in a chuck 41 which can be rotated via a ratchet-and-pawl device 50, 51, the ratchet 51 being actuated by means of a shaft 53 which is oscillated via a crank pin 55 formed on the engine crank-shaft 7. The pawl may be disengaged from the ratchet and the latter locked against rotation by means of a member 64, 65 secured to the valve 58. In operation, the valve may be turned to a first position in which the pawl is disengaged and the air in the chamber 28 is directed, via flushing chamber 40, through a bore 44 in the tool bit. In a second position, the pawl is engaged with the ratchet to rotate the drill and the air is fed to the chamber 28 to actuate the hammer piston 33 on its return stroke. In a third position, the hammer piston is permitted to operate but the pawl is disengaged and in a fourth position the air in the chamber is allowed to build up and instead of operating the hammer piston, it may be arranged to feed any external device.