A hammer assembly comprises a jack element substantially coaxial with an axis of rotation of a drill bit. The jack element includes a distal end extending beyond a working face of the drill bit. A porting mechanism within the bore comprises a first and second disc substantially contacting along a flat interface that is substantially normal to the axis of rotation. The first disc is attached to a turbine which is adapted to rotate the first disc with respect to the second disc. The first disc comprises a first set of ports adapted to align and misalign with a second and third set of ports in the second disc. As the first disc rotates, the sets of ports are adapted to route a drilling fluid into a piston chamber where a porting mechanism causes the jack element to repeatedly extend further beyond the working surface of the drill bit and then retract at a constant frequency.