| 摘要 |
<p>ENTERING END PORTION OF DRILL SCREW A drill screw having an integral driving shank, head, and entering end portion. The shank has formed on it thread convolutions of uniform outer and root diameters. The entering end portion has a cylindrical portion coaxial with the shank provided with two flutes inclined with respect to the center axis of the cylindrical portion and disposed on opposite sides of it, and end surfaces of a roof-shape. Each of the flutes includes conical flute surfaces. The intersection of each of the conical flute surfaces and each of the end surfaces forms a cutting edge. And each of the conical flute surfaces forms a rake angle with respect to one of the cutting edges, while each of the end surfaces forms a relief angle with respect to one of the cutting edges. In a preferred construction, each flute surface includes a cylindrical surface having an axis parallel to one of the end surfaces and a conical flute surface smoothly contiguous with the cylindrical surface. The intersection of each of the cylindrical surfaces and each of the end surfaces forms a cutting edge. Each of the cylindrical surfaces forms a rake angle with respect to one of the cutting edges, while each of the end surfaces forms a relief angle with respect to one of the cutting edges. In another preferred construction, each of the flute surfaces is made up of a plane surface and a substantially conical flute surface contiguous with the plane surface. The intersection of each of the plane surfaces and each of the end surfaces forms a cutting edge, and each of the plane surfaces forms a rake angle with respect to one of the cutting edges, while each of the end surfaces forms a relief angle with respect to one of the cutting edges.</p> |
