DRILL FOR DEEP HOLE BORING

摘要

PROBLEM TO BE SOLVED: To provide a twist drill capable of boring a deep hole having the depth of 20-40 times the diameter of the drill in a non-step manner. SOLUTION: The twist drill for boring a deep hole comprises first, second and third web thickness parts in which the web thickness is substantially constant from a tip side to the base end side of a blade part of the drill, the web thickness of the first web thickness part is larger than that of the second web thickness part, and the web thickness of the second web thickness part is larger than that of the third web thickness part.