| 摘要 |
A metal-working twist drill is provided with inner cutting edges that form a point (18) having an angle, A, of 130°. An outer, peripheral, part of each cutting edge (55, 57) forms an outer cutting portion (59, 61). The outer cutting portions slope in the opposite direction to the corresponding inner cutting edges and form an angle B, of 3° with respect to a plane normal to the axis of rotation of the twist drill. The width of the outer cutting portion, D as measured at the cutting edge, is 10.5% of the diameter of the twist drill. The metal-working twist drill produces bores having a reduced exit burr height. |
