Spline lubrication for DTH hammers

A down the hole drilling assembly having a top end arranged for coupling to a drill string and bottom cutting end, the drilling assembly comprising:

• an elongate casing;
• a fluid powered piston arranged moveably inside the casing, which is capable of shuttling axially back and forth, the piston having a piston nose positioned at an axially bottom end thereof;
• a top working chamber located at a top end of the piston and a bottom working chamber located at the bottom end of the piston;
• a driver sub provided with a set of axially extending driver sub splines on an internal surface thereof;
• a drill bit having a central bore extending axially therethrough and including an elongate shank provided with a set of axially extending shank splines on an outer surface thereof for engagement with the driver sub splines to form a spline area;
• a guide sleeve arranged for forming a first seal with the piston nose, wherein the guide sleeve has an inner surface and an outer surface, wherein the guide sleeve forms a second seal with the outer surface of the shank of the drill bit;
• and
• at least one air passageway extending through the guide sleeve and the casing or just the casing for fluidly connecting the bottom chamber to the spline area to provide lubrication thereto, wherein the guide sleeve has a first section at the axial top end, a second section in an axial central region and a third section at the axial bottom end and wherein the air passageway is formed from:
• at least one top end port located in the first section that extends from a first distal end on an inner surface of the guide sleeve to a second distal end on the outer surface of the guide sleeve and wherein the first distal end is fluidly connected to the bottom chamber;
• at least one channel positioned in the second section formed between an inner surface of the casing and the outer surface of the guide sleeve that is fluidly connected to the at least one top end port;
• and
• at least one groove positioned in the outer surface of the third section or at least one bottom end port extending through the third section that is fluidly connected to the channel and the spline area.