| 摘要 |
A twist drill having a longitudinal axis and major flanks ground by helical face grinding by means of a grinding wheel having a grinding face perpendicular to its axis of rotation and a circumferential profile, each major flank terminating in a cutting edge and having a surface which defines a clearance angle relative to the cutting edge wherein: the drill has an outer diameter and a central solid core having a thickness equal to 25% to 40% of the outer diameter; and each major flank is ground by a grinding operation performed by rotating the grinding wheel while its grinding face forms the major flank, effecting angular movement of the drill about its longitudinal axis and relative to the axis of rotation of the grinding wheel, effecting relative radial movement between the grinding wheel and the drill in the direction perpendicular to the drill axis and away from the axis of rotation of the grinding wheel, and effecting axial movement of the drill along its longitudinal axis toward the grinding wheel in a progressively increasing manner, such that the clearance angle defined by the finished major flank surface increases progressively with increasing distance from the cutting edge. |
