| 摘要 |
A twist drill (20) is provided which has an improved tip (26) including at least one spiral groove (42) which extends from the leading face of a cutting edge of a tip portion of the drill. This groove is positioned at a spaced location from the cutting lip (40) and extends to the trailing face of the cutting blade tip such that a portion of the material to be drilled initially passes through the spiral groove (42) during the drilling operation as the drill is fed into the work piece. The portion of the material which passes through the groove (42) is at least partially cut by a subsequent pass of the cutting edge of the further cutting blade tip and causes shavings of the material to be broken into smaller sizes thereby enhancing the travel of the shavings along the length of the flutes (70') and reducing the binding forces applied to the twist drill during drilling operations. The flutes (70') are also enlarged in accordance with a specified criteria to enhance the drilling efficiency.
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