A rotary well-drilling bit lowered through a drill string to a special orienting, positioning and aligning sub attached to the bottom of the drill string with the aid of mud pressure with the bit approximately 90.degree. from its normal operating position. The drill bit is prepositioned before entering...http://www.google.de/patents/US4651837?utm_source=gb-gplus-sharePatent US4651837 - Downhole retrievable drill bit
