Cutters and bits for terrestrial boring

A bit having at least one cutter for cutting a formation, said cutter comprising:

• a longitudinally and laterally extending mount section;
• a cutting section for cutting the formation as said bit is rotated;
• a cap of super-hard material carried over one longitudinal end of said mount section;
• a leading surface included on a side wall of said cap;
• and
• a curving cutting face in the form of a surface of revolution formed by a concave line formed on said leading surface for engagement with uncut formation, said cutter being oriented on said bit such that a major volume of said super-hard material in said cap is disposed rearwardly of said cutting face as said cutter is rotated into cutting engagement with the formation.

A bit having at least one cutter mounted on a supporting bit body for cutting a formation, said cutter comprising:

• a cutting section for cutting a formation as said bit is rotated;
• a leading section on an axial end of said cutting section forming a substantially planar cutting face for engaging said formation;
• and
• a trailing side section on a lateral side of said cutting section extending between said axial end section and said bit body, said trailing side section including a surface in the form of a surface of revolution of a concave-shaped arc section relative to the axis of said revolution, said surface of revolution forming a convex line when said surface of revolution is intersected with a plane normal to said axis of revolution.

A rotary, fixed cutter bit having at least one cutter mounted on said bit for continuous rotary engagement against a formation, said cutter comprising:

• a mount section for securing said cutter to said bit;
• a cutting section for cutting the formation as said bit is rotated;
• a leading surface area included in said cutting section;
• and
• a concave cutting face on said leading surface area for engagement with uncut formation, said cutting face having the form of an external surface that forms a convex line of intersection with a first plane passing through said external surface along a first dimension and a concave line of intersection with a second plane passing through said external surface along a second dimension where said first and second planes also intersect on said external surface.