Patent attributes
A hollow piston drive mechanism for a hammer drill comprises a crank pin 54 having a cylindrical link member 68 rigidly connected to a part-spherical bearing 70. The part-spherical bearing 70 is slidably and rotatably disposed in a part-spherical recess 72 formed in the crank plate 52, as a result of which the bearing 70 can be easily mounted to the recess 72. The cylindrical link member 68 is slidably disposed in a cylindrical bearing 56 formed in the end of the hollow piston 58. The crank pin 54 is therefore able to rock back and forth in the spherical recess 72 as well as slide up and down in the cylindrical bearing 56. A cylindrical collar member 74 is mounted on the cylindrical link member 68 of the crank pin 54 and is moveable between a lower position in which it abuts the upper surface of the part-spherical bearing 70 and an upper position in which it abuts and the underside of the cylindrical bearing 56 so that the crank pin 54 is prevented from moving out of engagement with the part-spherical recess 72 formed in crank plate 52. The cylindrical collar member 74 can be mounted to the crank pin 54 after construction of the crank plate 52 and crank pin 54 assembly.
