| 摘要 |
The invention relates to a twist drill for short hole drilling including two chip flutes that open in a clearance surface of a front tip so as to form, together with the clearance surface, two cutting edges. The chip flutes have been given a unique shape so far that three different part surfaces (19, 20, 21) have different curvatures. More precisely, a bottom surface (21) has an arc radius less than 10 mm, while the two other ones (19, 20) have a radius of curvature that approaches infinity. A boundary line (22) between the concave bottom surface (21) and a heading frontal surface (19) meets a main edge that is included in the individual cutting edge and divided into two edge segments that together impart a J-like shape to the main edge. The chip flute is extraordinary deep by the fact that the diameter (DC) of the core (9) of the drill has been reduced to a minimum at the same time as the opening angle (±) of the chip flutes has been made smaller than the angle of divergence (²) of two bars (7), between which the flutes are countersunk. By these features, the formation and the evacuation of the chips is improved, above all so far that these do not hammer against the generated hole wall (HW). In addition, the drill is easy-cutting and requires a minimum of energy. |
