To provide a boring tool capable of preventing seizure of a stem guide hole by regulating surface roughness of a finishing surface of a bored hole within an optimum range for securing lubrication oil during a finish process of the stem guide hole.
A reamer inserted in a lower hole formed in a cut material in advance for cutting an inner wall surface of the lower hole and forming a processing hole includes cutting blades 31 and three bearing parts 26 at a constant interval in a circumference direction. The surface roughness of each bearing part 26 is set within a range of 1.1-1.4 m in terms of Rz value, and sum W26 of width in a tool circumference direction of a plurality of the bearing parts 26 is set within 0.15D to 0.45D mm to an outer diameter D of the cutting blades 31.
MITAMURA MITSUHIRO
MITSUBISHI MATERIALS TOOLS COR
Tadashi Takahashi
Yasuhiko Murayama
Noriko Yanai