| 摘要 |
A drill has first, second and third teeth each tooth having a cutting edge at its front end. The cutting edge of the first tooth extends all the way to a center axis of the drill; the cutting edges of the second and third teeth have inner ends spaced from the axis to form a space between one another. A cooling channel extends axially through the drill until approaching the front end of the drill whereupon it becomes inclined relative to the axis and forms an exit port in the space. |
