Importance

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Abstract

A rotating boring tool (10) comprises a cylindrical shank (11) and a body (12), both of which are coaxial with each other, said body being provided at its tip end with cutting blades (13a, 13b) which are in point symmetry with respect to an axis of the shank. Provided on the body are two flutes (14a, 14b) continuous from the cutting blades. The both flutes are made to approach each other at the lower half lead portions (designated hereinbelow as f1 portions) of terminal end portions f0 of the flutes and positioned about 35 degrees or more offset from the position of point symmetry. Alternatively, the both flutes are merged at the f1 portions. Accordingly, thickened portions y0 are formed on the f1 portions to increase rigidity of the f1 portions. As a result, it is possible to suppress generation of fatigue failure at the f1 portions whereby a rotating boring tool of long service life which is hard to break is obtained and a product cost and a cost for tool replacement are considerably reduced.

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First Claim