DRILL FOR FORMING THROUGH HOLE IN MAGNETIC SUBSTANCE

To provide a drill which can inhibit surface roughness of a side wall of a through hole near a penetration side end of a magnetic substance.SOLUTION: A drill for forming a through hole in a magnetic substance is used to form a through hole in a magnetic substrate used for a printed wiring board. A drill tip includes four flat surfaces. Two surfaces of the four flat surfaces are tip flanks which extend from a center of the drill tip to a drill side surface and respectively form tip cutting edges with ridge lines with two spiral chip discharge grooves on the drill side surface. The other two surfaces of the four flat surfaces are belt-like extrusion surfaces which extend from the center of the drill tip to the two spiral chip discharge grooves along the tip flanks and have a constant width.SELECTED DRAWING: Figure 1 【課題】磁性体の貫通側端部付近の貫通孔側壁の表面粗さを抑制できるドリルを提供すること。【解決手段】プリント配線板に用いられる磁性体に貫通孔を形成するための磁性体貫通孔形成用ドリルであって、ドリル先端が４つの平坦面を備え、前記４つの平坦面の内の２面は、前記ドリル先端の中心からドリル側面まで延在し、そのドリル側面の螺旋状の２条の切り屑排出溝との稜線でそれぞれ先端切れ刃を形成する先端逃げ面であり、前記４つの平坦面の内の他の２面は、前記ドリル先端の中心から前記先端逃げ面に沿って前記螺旋状の２条の切り屑排出溝まで延在する一定幅の帯状の押し出し面である。【選択図】図１