PURPOSE: To prevent breakage of the cutting edge at the center of a drill by combining an extra-hard alloy, which suits to characteristics of the drill, complexly with the drill proper and solidly from the metallurgical point of view.
CONSTITUTION: The body 2 of a drill 1 is formed by an extra-hard alloy, and the tip of the body has a small diameter approx. the same as thickness l of the web for a length comparative with the re-grinding amount of the drill, and a chisel 3 is fixed to the tip. A grinding part 4 to provide standard thickness for the tip web thickness according to necessity. Thereby it can stand with excessive thrust force sufficiently, as well as be secured with less likelihood of breakage of the central cutting edge and wear of the peripheral cutting part, to ensure highly efficient machining at a high revolving speed with large thrust force.
MORI YOSHIKATSU
KUNIMORI NAGATOSHI
MARUYAMA MASAO
