| 摘要 |
PURPOSE:To improve machining efficiency extremely and machining accuracy also by providing abrasive grains in such a way that the diameters of the abrasive grains consisting of an abrasive grain layer are gradually reduced as the diameter of each of small diameter machining sections increases in external diameter. CONSTITUTION:When a core drill CD rotated in the direction of an arrow 18 and applied ultrasonic waves thereto is lowered in the direction of an arrow 19a toward the work piece 20 fixed to a bed 21, the rough cutting section of the core drill CD makes a prepared hole on the work piece 20. In the next step, when the finish cutting section of the core drill reaches the opening of the prepared hole, the internal wall face of the prepared hole is finished by the finish cutting section to form a small diameter hole 23. Being thus capable of rough cutting and finish cutting continuously at one time to obtain the small diameter hole 23, the core drill CD can improve machining accuracy as well as machining efficiency extremely compared with the case that rough cutting and finish cutting are performed separately. |
