| 摘要 |
The instrument has a tapering shank (1) with a spiral cutting edge along at least part of its length, forming its active section, and an angle of taper which is greater at the rear of the shank than at its tip. The shank has two sections with different angles of taper, each one increasing from the forward end of the section to its rear end, and it has the shape of a body of revolution with a generating line in the shape of a curve with a tangent at any point forming an angle with the instrument's lengthwise axis which increases from its tip to its rear end. In addition its tip, which has no cutting edge, has a spiral groove for removing material detached by the drill. |
