CEMENTED CARBIDE DRILL BIT

摘要

The ratio of the diameter c of the web portion (1) to the drill diameter d is set in the range of 25% to 35%. The flute width ratio (b:a) is set in the range of 0.4:1 to 0.8:1. To decrease the cutting resistance on the drill, the radial rake theta r angle of the cutting lip (4) measured at positions spaced at least 2/3 of the drill diameter toward the outer peripheral side is set in the range of -5 deg. to positive values. To promote the chip ejecting function, the relative distance (L) between the cutting lip (4) and the flute wall (5) opposed to it is decreased.