Drill for drilling brittle materials

摘要

A drill head carries a plurality of coaxially mounted drill crowns beginning with a first crown and followed by additional drill crowns which, upon rotation, describe concentric envelope circles of successively larger diameters. The first drill crown has cutting elements with a diamond coating with an average particle size of 200-1,000 mu m, and the additional drill crowns have cutting elements with a diamond coating with an average particle size of 200-300 mu m. The difference in diameter of succeeding drill crowns is successively small. Alignment of the drill crowns in a pilot hole is achieved by guide elements mounted behind the drill crowns and describing an inner envelope circle which is smaller than the outer envelope circle described by the largest drill crown, thereby defining a radial safety gap into which fluid is fed to form a cushion during rotation.