| 摘要 |
The cutting part (1) of a twist drill is provided with a turned groove (3) for circular milling. Backward cutting edges (14, 15) incorporated in the transition steps (8, 9) between the cutting part (1) and the turned groove (3) have faces (16) which extend radially inward toward the axis (18) of the drill from the cutting part (1) of the drill beyond the diameter (4) of the turned groove into the twisted grooves (6, 7). |
