A drill bit assembly comprising a plurality of cutter units, with each cutter unit comprising a circumferentially forward, relatively blunt positioning cutter, followed by a fixed cutter having a relatively sharp cutting edge, with the cutting edge of the following cutter being positioned a predetermined...http://www.google.fr/patents/US5595252?utm_source=gb-gplus-shareBrevet US5595252 - Fixed-cutter drill bit assembly and method
