Drill tool

A drill tool for rotary and/or percussion drilling, comprising

• a drill string rotatable about a longitudinal axis;
• and
• a cutting apparatus connected to a lower longitudinal end of said drill string, said cutting apparatus including:
• a guide portion for guiding said cutting apparatus within a casing tube which surrounds the drill string during a drilling operation, a pilot bit disposed at a lower longitudinal end of said cutting apparatus,
• an intermediate portion disposed between said guide portion and said pilot bit and being of smaller cross section than said guide portion, said intermediate portion being rotatable with said drill string and including an outer surface,
• a hollow reamer mounted eccentrically on said intermediate portion for rotation relative thereto about a longitudinal axis, said reamer including an inner surface facing said outer surface, and
• means for driving said reamer comprising a generally radially outwardly projecting tongue on said outer surface and a pair of circumferentially spaced shoulder surfaces disposed on said inner surface in the path of rotation of said tongue so as to be selectively engaged by said tongue in response to rotation of said drill string in opposite directions relative to said reamer;
• said tongue being engageable with each of said shoulder surfaces along an area of contact having an upper longitudinal end which terminates below an uppermost end of said reamer, and a lower longitudinal end which terminates above a lowermost end of said reamer.

A drill tool for rotary and/or percussion drilling, comprising

• a drill string rotatable about a longitudinal axis;
• and
• a cutting apparatus connected to a lower longitudinal end of said drill string, said cutting apparatus including:
• a guide portion for guiding said cutting apparatus within a casing tube which surrounds the drill string during a drilling operation,
• a pilot bit disposed at lower longitudinal end of said cutting apparatus,
• an intermediate portion disposed between said guide portion and said pilot bit and being of smaller cross section than said guide portion, said intermediate portion being rotatable with said drill string and including an outer surface;
• a hollow reamer mounted eccentrically on said intermediate portion for rotation relative thereto about a longitudinal axis, said reamer including an inner surface facing said outer surface, and
• means for driving said reamer comprising a generally radially inwardly projecting tongue on said inner surface and a pair of circumferentially spaced shoulder surfaces arranged on said outer surface such that said tongue lies in a path of rotation of said shoulder surfaces and is engaged by said shoulder surfaces in response to rotation of said drill string in opposite directions relative to said reamer;
• each of said shoulder surfaces being engageable with said tongue along an area of contact having an upper longitudinal end which terminates below an uppermost end of said reamer, and a lower longitudinal end which terminates above a lowermost end of said reamer.