| 摘要 |
<p>A self-drilling and self-tapping screw has a compound flute configuration. Each flute (16, 18) has, in cross-section, a straight portion (28, 30) including at least part of the cutting edge and a curved portion (32, 34) defining the drag edge. The screw has a convex point configuration produced by a profiled toothed milling cutter (66) having uniformly radiused heels or, alternatively, heels which are formed by two planar surfaces (62, 64) intersecting to enclose an obtuse angle less than 180 DEG . Fluting milling cutters are introduced by movement not radial to produce the straight portions of the flutes the flutes being at an angle to the screw axis. Special milling cutters with arcuate portions and ribs formed by teeth produce chip breaking grooves int the flutes. <IMAGE></p> |
