A rotary drill bit for drilling subsurface formations comprises a bit body having a shank for connection to a drill string, a plurality of primary blades and at least one secondary blade circumferentially spaced and extending outwardly away from a central axis of rotation of the bit, a plurality...http://www.google.es/patents/US5816346?utm_source=gb-gplus-sharePatente US5816346 - Rotary drill bits and methods of designing such drill bits
Rotary drill bits and methods of designing such drill bits
