HARD ROCK DRILLING - SOME RECENT TEST RESULTS.

The results of a series of tests are presented on using diamond abrasives when drilling Cornish grey granite at constant penetration rate or constant thrust loads. The results confirmed earlier findings that, by setting the penetration rate of impregnated drill bits, efficient drilling can be maintained throughout the life of the bit. The program indicates that the measurement of torque is a key parameter in assessing the condition of a drill bit. At constant penetration rates, it is essential for bit load fluctuation to occur in order to keep the bit 'open'.