PROBLEM TO BE SOLVED: To process a plurality of prepared holes which are axially spaced apart from each other, into finish holes at low cost and efficiently by means of a long boring tool.;SOLUTION: In the vicinity of a free end portion 26 of a long tool body 12, a support sleeve 40 is fitted so as to be axially slidable and relatively rotatable. The support sleeve 40 includes bearing parts 42, 44 in both axial end portions and an expanded part 46 in an intermediate portion. A diameter of an inner peripheral surface of the bearing part 42 is smaller than that of the bearing part 44, and each of both the bearing parts 42, 44 has a hydrostatic pressure bearing function. A pressurized coolant is supplied to an internal space 48 of the expanded part 46, the support sleeve 40 is moved into a finish hole 90 and abutted to a stepped surface 70, thereby increasing pressure in the internal space 48. The expanded part 46 is diameter-enlarged, coupled and fitted into the finish hole 90. In such a state, boring is performed on a prepared hole 100 by a cutting blade 32 in the free end portion 26 of the tool body 12, such that the prepared hole 100 is processed into the finish hole 90.;COPYRIGHT: (C)2014,JPO&INPIT
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