Power-driven hand tool

A power-driven hammer drill, comprising a housing;

• a tool chuck on said housing and adapted to hold an elongated tool;
• means for impacting said tool chuck in direction lengthwise of the tool, including a guide tube coaxial with said tool chuck, and a piston which is slidingly received and reciprocable in said guide tube in said direction, said piston having one end portion facing towards said tool chuck and another end portion facing away therefrom, said other end portion being formed with a bore extending transverse to said direction;
• and drive means for said impacting means, comprising a driven rotatable shaft mounted for rotation about an axis paralleling said direction, a drum coaxially mounted on said shaft freely turnably surrounding the same and having a circumferential surface formed with a circumferentially complete cam track formed as a groove having an axial flank shaped to act as a wobble plate, coupling means for coupling said drum for joint rotation with said shaft, and transmitting means guided by said cam track and operatively connected with said piston for transmitting reciprocatory motion to the same in response to rotation of said drum with said shaft, said transmitting means comprising a ring freely turnably received in said groove and a projection extending substantially radially from said ring and slidably received in said bore of said other end portion of said piston, said coupling means comprising cooperating first and second coupling portions on said shaft and said drum, respectively, and said shaft being axially shiftable relative to said drum between two positions in which said first and second coupling portions are engaged and disengaged, respectively.