The hammer drill has a spindle (14) mounted in a housing (10) which is driven by a motor (12). The spindle can move axially a defined distance within the housing. On the spindle is a rotating cam assembly (3). A coupling cam component (2) can move axially along the spindle and a pressure spring holds the coupling component against the cam assembly in the axial direction. On the rotating cam assembly are two cams (3b,2b) which work in conjunction with each other such that when the spindle turns the coupling component returns to the cam assembly and moves some distance from it. The coupling cam component then acts on the spindle to vibrate it in the axial direction. The weight of the coupling cam and the tension strength of the spring are determined on the basis of a given ratio of the first to the last of 6.
