SPLINE LUBRICATION FOR DTH HAMMERS

A down the hole drilling assembly has a top end coupled to a drill string and a bottom cutting end. The drilling assembly includes a piston arranged moveably inside a casing with a piston nose positioned at an axially bottom end and a top working chamber at a top end, a bottom working chamber at the bottom end, a driver sub having axially extending driver sub splines on an internal surface, a drill bit having an axially extending central bore including an elongate shank provided with axially extending shank splines on its outer surface for engagement with the driver sub splines to form a spline area, a guide sleeve forming a seal with the piston nose, the guide sleeve having an inner and outer surface, and at least one air passageway extending through the guide sleeve for fluidly connecting the bottom chamber to the spline area to provide lubrication thereto.