| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill for a printed circuit board, which drill can improve the positional accuracy of a drilled hole, and can prevent the deterioration of the surface roughness of the drilled hole due to the deterioration of the discharge-ability for chips. SOLUTION: The drill for the printed circuit board comprises a body 1 and a shank portion 2. A pair of flutes 3 are provided on the outer peripheral surface of the body 1 on both sides of the axis of the drill so as to be extended from the tip end surface toward the base end side, and cutting edges 10a are formed on the crossed ridge lines of the flutes 3 and the tip end surface of the body 1 respectively. The diameter W of the minimum inscribed circle to be inscribed to the wall surfaces 4 of a pair of the flutes is set within a range from 45 to 65% of the outside diameter D of the cutting edges when the cross section perpendicular to the axis of the drill is viewed from the tip end side. The shape of the flutes 3 is a reversed S shape composed of the concave line portion 4a provided on the leading edge 13 side and the convex line portion 4b provided on the heel 14 side. COPYRIGHT: (C)2009,JPO&INPIT
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