| 摘要 |
PROBLEM TO BE SOLVED: To prevent a finished article from getting surface coarseness and spoiling quality when swarfs strike on the inner face of a finished hole even in the case of producing slightly extended swarfs.SOLUTION: A swarf discharge groove 5 is formed in the tip outer periphery of a drill body 1 rotated around the axis O to provide the tip of a wall face 5a directing in the drill rotation direction T of this swarf discharge groove 5 with a cut blade 6, and the tip outer periphery of a wall face 5b directing reversely to the drill rotation direction T of this swarf discharge groove 5 with a swarf control wall 9 smaller in the outer diameter around the axis O than in the outer diameter of the cut blade 6 with the tip edge located on the rear end side of the cut blade 6 in the axis O direction to extend oppositely in the drill rotation direction T to face the rake face of the cut blade 6.SELECTED DRAWING: Figure 4 |
