| 摘要 |
<p>A drilling tool which comprises: a cylindrical structure having a spiral groove provided on the outer surface thereof and at least one elongated rectangular through-hole provided in the lower portion thereof; a tip which is loosely fitted into said through-hole in such a manner that a cutting edge of said tip faces outside, the number of said tips being equal to the number of said through-holes; a tip guide bar having a head portion and a taper slit which is tapered downwardly starting from a part of the lower surface of said head portion so as to accommodate said tip therein, said part being in the vicinity of the axial line thereof, said tip guide bar being inserted into the lower end portion of said cylindrical structure in such a manner that said tip is pushed outwardly by the tip guide bar, said tip guide bar being engaged with the upper and inner portion of said tip so that said tip guide bar is slidably connected to said cylindrical structure; and a taper shank inserted into the upper end portion of said cylindrical structure and fixedly fastened thereto so as to be held by a motor-driven drill.</p> |
