GUN DRILL AND GUN DRILL MACHINE, AND DRILLING METHOD

PROBLEM TO BE SOLVED: To provide a gun drill capable of preventing a malfunction at the time of drilling without losing the original shape of a blade tip even if the number times of polishing is increased, and to provide a gun drill machine with a polishing device capable of polishing the gun drill efficiently, and a drilling method for preventing the loss of the blade tip of the gun drill at the time of drilling. SOLUTION: A stepped part 22 is formed at a crossing section 17c positioned on the extension line of a blade 15, and a second front end flank 17b is formed on this side in the drilling direction relative to a first front end flank 17a. This can inhibit the cross section 17c from being displaced to the second front end flank 17b side as it has been displaced before, and can prevent a malfunction at the time of drilling even if the number of times of polishing of an inner cutting blade 14 is increased. Moreover, the gun drill with a chamfer formed at an outer corner is used when a crossing hole is formed, thus preventing the loss of the blade tip. Furthermore, the polishing device with the gun drill machine is arranged opposedly to a gun drill pay-out device, thus improving the working efficiency of polishing drastically. COPYRIGHT: (C)2008,JPO&INPIT