A hammer drive mechanism for a hammer strike mechanism of a hammer drill comprising: a drive shaft capable of being rotationally driven by a motor; a rod (23, 306) capable of reciprocatingly driving a piston; a conversion mechanism (25, 27; 302) which converts the rotary movement of the drive shaft into a reciprocating movement of the rod (23;306); wherein the drive shaft comprises a first part (120; 308) connected to the conversion mechanism (25, 27; 302) and a second part (122; 310)), the second part (122; 310) capable of being rotationally driven by a motor; wherein the second part (122, 310) connects to the first part via at least one dampener wherein the rotary movement of the second part (122; 310) is transferred to the first part (120; 310) via the at least one dampener; wherein the first part (120; 308) of the drive shaft comprises at least one first projection such that rotation of the first part (120;308) results in rotation of the at least one first projection; wherein the second part (122; 310) of the drive shaft comprises at least one second projection such that rotation of the second part (122; 310) results in rotation of the at least one second projection; wherein rotation of the second part (122; 310) results in the rotation of the at least one second projection towards the at least one first projection; wherein at least part of the at least one dampener locates between the first and second projections (128, 138) so that the rotation of the second part (122; 310) is transferred to the first part (120; 308) by the at least part of the at least one dampener transferring the rotary movement of the at least one second projection to the at least one first projection; wherein there are at least two first projections and at least two second projections, the number of first and second projections being equal; wherein the projections are arranged on a circular path around the axis of rotation of the drive shaft; wherein each of the first projections on the first part (120, 308) locates between two of the projections on the second part (122, 310) and each of the second projections on the second part locates between two of the first projections on the first part so that the first and second projections are arranged in an alternate manner around the axis; wherein at least part of at least one dampener is located between adjacent projections; characterised in that the at least one dampener comprises two square pegs interconnected with an arcuate tether formed in a one piece construction wherein the square pegs form the at least part of the at least one dampener located between adjacent projections (128, 138). a drive shaft capable of being rotationally driven by a motor; a rod (23, 306) capable of reciprocatingly driving a piston; a conversion mechanism (25, 27; 302) which converts the rotary movement of the drive shaft into a reciprocating movement of the rod (23;306); wherein the drive shaft comprises a first part (120; 308) connected to the conversion mechanism (25, 27; 302) and a second part (122; 310)), the second part (122; 310) capable of being rotationally driven by a motor; wherein the second part (122, 310) connects to the first part via at least one dampener wherein the rotary movement of the second part (122; 310) is transferred to the first part (120; 310) via the at least one dampener; wherein the first part (120; 308) of the drive shaft comprises at least one first projection such that rotation of the first part (120;308) results in rotation of the at least one first projection; wherein the second part (122; 310) of the drive shaft comprises at least one second projection such that rotation of the second part (122; 310) results in rotation of the at least one second projection; wherein rotation of the second part (122; 310) results in the rotation of the at least one second projection towards the at least one first projection; wherein at least part of the at least one dampener locates between the first and second projections (128, 138) so that the rotation of the second part (122; 310) is transferred to the first part (120; 308) by the at least part of the at least one dampener transferring the rotary movement of the at least one second projection to the at least one first projection; wherein there are at least two first projections and at least two second projections, the number of first and second projections being equal; wherein the projections are arranged on a circular path around the axis of rotation of the drive shaft; wherein each of the first projections on the first part (120, 308) locates between two of the projections on the second part (122, 310) and each of the second projections on the second part locates between two of the first projections on the first part so that the first and second projections are arranged in an alternate manner around the axis; wherein at least part of at least one dampener is located between adjacent projections; characterised in that the at least one dampener comprises two square pegs interconnected with an arcuate tether formed in a one piece construction wherein the square pegs form the at least part of the at least one dampener located between adjacent projections (128, 138).