Patent ID: 8651197

Claim:
A manually operated hammer drill comprising: a spindle ( 3 ) that drives a chuck ( 5 ) in a rotary manner about an axis of rotation ( 6 ) in a drilling mode, a pneumatic hammer mechanism ( 4 ), that hammers against a tool inserted in the chuck ( 5 ) in a hammer mode, wherein the hammer mechanism ( 4 ) has a piston ( 10 ) which performs reciprocating movements ( 12 ) parallel to the axis of rotation ( 6 ) in a cylinder ( 11 ) conformed inside the spindle ( 3 ) when the hammer mode is activated, wherein the piston ( 10 ) has at least one radial groove ( 21 ) in which an annular seal ( 22 ) is arranged, and the radial groove ( 21 ) has a cross-sectional profile ( 24 ) that is larger parallel to the axis of rotation ( 6 ) than a cross-sectional profile ( 27 ) of the annular seal ( 22 ) and which is furnished with a middle area ( 31 ) disposed midway within the radial groove at the groove base ( 26 ) that is at a maximum distance ( 32 ) from the cylinder ( 11 ) and end areas ( 33 , 34 ) that taper radially outward from the middle area ( 31 ) and are at a smaller distance ( 35 ) from the cylinder ( 11 ), than the maximum distance ( 32 ).