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INTRODUCTION A method of rotary drilling in rock, usually for exploratory purposes using hollow diamond-crowned bits to obtain a core for examination Core is brought to the surface by a core barrel

Mechanism of core extrraction The drill extends into a drill rod, which has a diamond drill bit on the end. The drill uses rotary action to provide power to force the drill bit into the ground. As the drill bit penetrates the Earth and the drill rod slides in, a core is forced through the hole in the middle of the drill bit. The core then continues sliding into the drill rod. Inside each drill rod is a wire mechanism. This is used to contain and recover the core sample inside. Without this catching mechanism, bringing the core to surface could be very difficult.

When one drill rod is completely in the ground, another is usually screwed to the top of it allowing deeper penetration. Once all the necessary drill rods have been filled with cores, they are retrieved from the ground. They are generally stored in sectional boxes that correlate to the drill rod from which they were obtained

Tube sizes There are five major "wire line" tube sizes typically used. Larger tubes produced larger diameter rock cores and require more drill power to drive them. The choice of tube size is a trade-off between the rock core diameter desired and the depth that can be drilled with a particular drilling rig motor.

Standard "Q" wire line bit sizes (outside) hole diameter, mm Core diameter, mm Aq 48 27 Bq 60 36.5 Nq 75.8 47.6 Hq 96 63.5 pq 122.6 85

Collected cores

conclusion This can be used to drill for greater depth Since the diamonds are hard the deviation while drilling is minimum