TWO-BLADE TWIST DRILL WITH DOUBLE MARGINS

PROBLEM TO BE SOLVED: To provide a two-blade twist drill of a double margin structure capable of suppressing hole curving by exerting the effect of the double margins in deep hole machining and special intermittent machining for cutting a workpiece with a drill again after passing the drill through the workpiece once, and suppressing fretting resistance due to the margins. SOLUTION: The first margin 8 and the second margin 9 are provided in a drill normal rotating direction front edge part of a land part 7 and in the middle part of the peripheral direction of the land part 7, respectively. Both of the first margin 8 and the second margin 9 are extended near a terminal end of a twisted groove 6 to be parallel with the twisted groove 6. The second margin 9 is arranged at a position rotated by θ=45-80° in a drill reversing direction from the position of the first margin 8. COPYRIGHT: (C)2007,JPO&INPIT