Abstract: In a percussion tool for rock drilling there is used in place of the conventional, large bore crown a hammer body (18) carrying a great number of interchangeable small bore crowns (26a,26b). The impact of a hammer piston (22) is transferred to the hammer body (18) which contains a radially projecting thicker head (25) to which the bore crowns (26a,26b) are secured. If individual bore crowns are worn or damaged, they can be interchanged individually. Moreover, the bore crowns can be rotated so as to position corresponding other hard metal elements (33) into the marginal area of the percussion tool.

Abstract: An annular drilling hammer having an annular bore crown guided between an outer tube and an inner tube. An annular hammer piston periodically strikes the bore crown and has a piston member that is guided in a cylindrical chamber having control apertures which are connected fluidically to a reversing valve. The working medium is delivered to the reversing valve between an inner tube system and an outer tube system. After driving the hammer piston the medium is discharged from the drill between the outer tube and the bore crown. The bore crown is provided with flow channels leading from the rear shoulder through and to the front and/or central aperture of the bore crown. The flow of driving medium through these channels aids the entrainment of bored material, which then is carried out through the inner tube with the aid of a Venturi opening.