The down-the-hole hammer drill is a pneumatically operated bottom-hole drill that efficiently combines the hitting action, similar to that of cable tool drilling, with the turning action of rotary drilling. The pneumatic drill can be used on any standard rotary rig with an integral or auxiliary air compressor of sufficient capacity. It is used for fast and economical drilling of medium to extremely hard formations. Fast penetration results from the air piston blows transmitted directly to the bit, so practically no energy is wasted in chewing up cuttings. A straight hole is assured by short, rapid blows that minimise the effect of dipping and broken formations. Down-the-hole hammer drilling is by far the fastest method of penetration in hard rock material. The bit is turned slowly (10 to 15 RPM) by the same method that rotates the drill bit in the mud or air drilling operation.
