PURPOSE: To prevent the breakage of a chisel edge and enable the high-speed cutting by consolidating extremely-hard alloys matching the characteristics of a drill compositely and metallurgically to constitute the drill.
CONSTITUTION: A stiff, extremely-hard alloy 5 is used for a non-cutting section at the center with a slow cutting speed, and on the other hand an extremely- hard alloy superior in abrasion resistance to the said extremely-hard alloy and a steel shank 6 are used for the tip periphery with a high cutting speed to form this drill. Thereby, specific features of each raw material can be satisfactorily exerted. Accordingly, it can thoroughly withstand an excessive thrust force, the breakage of the central edge and the abrasion or deterioration of the peripheral cutting section is reduced, and it can withstand high-speed rotations under a strong thrust force.
MARUYAMA MASAO
MUKAI YOSHINOBU
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