Mechanisms of rock cutting
Bits and coreheads cut rock by crushing, shearing, grinding or jetting. Crushing bits are the well known roller cone bits and hammer bits.
1 Crushing bits - roller cone rock bits
Crushing bits work by crushing the rock to make an indentation with a tooth and then scouring the rock away with the subsequent tooth movement. The harder the rock the smaller the indentations and the slower the drill rate per revolution. Rocks have a certain threshold pressure which is required to initiate the indentation of each tooth. Thus a tri-cone bit needs . . .