US Patent 7901163 Gun drill

A gun drill having excellent cutting efficiency, having high deep-hole drilling efficiency, and having a prolonged blade service life has a cutter head having a coolant discharge port communicating with a coolant supplying path at the distal end face at the distal end of a hollow shank portion having a cutting chip discharge groove, whose section along the lengthwise direction is V-shaped, on the outer surface and having the interior thereof made into a coolant supplying path, wherein a blade portion of the cutter head is made of cemented carbide alloy, and at the same time, the guide pads and that are brought into sliding contact with the inner circumference of a cutting bore are composed of a dissimilar material having higher hardness than the cemented carbide alloy.