| 摘要 |
A drilling tool includes a basic body defining a center axis of rotation and having two chip channels and two replaceable indexable cutting bits in the form of a center bit and a periphery bit mounted in respective center and periphery pockets formed in an axially front end of the basic body. The center bit and the center pocket are spaced radially from the periphery bit and the periphery pocket along a first diametrical plane of the basic body. At least the center bit includes four identically-shaped cutting edges, one of which constituting an operative cutting edge intersected by a second diametrical plane oriented perpendicularly to the first diametrical plane. Each cutting edge of the center bit comprises first and second part edges joined by a transition edge portion. The first and second part edges of the operative cutting edge constitutes operative first and second part edges, respectively; the operative first part edge being spaced from the center axis and situated closer than the operative second part edge to an outer periphery of the basic body. An axially forwardmost portion of the operative first part edge is disposed axially forwardly of an axially forwardmost portion of the operative second part edge, and an axially forwardmost portion of an operative cutting edge of the periphery bit lies axially between the axially forwardmost portions of the operative first and second part edges of the center bit, respectively. |
