| 摘要 |
A self-drilling screw comprising a threaded shank having a head at one end and a forged drill bit at the other end, the drill bit including a pair of oppositely disposed intrusion faces and a pair of oppositely disposed axial flutes, a chisel edge formed at a lower extremity of the drill bit and divided into two parts by a downwardly projecting apex formed on the chisel edge, the two parts extending from the apex in the opposite directions and each being slightly inclined to provide an inclination angle formed between itself and a workpiece surface, the inclination angle being within the range from 5 DEG to 20 DEG , the drill bit further including a pair of oppositely disposed vertical flat rake faces which substantially adjoin each other at an adjoining point disposed on the chisel edge and which extend upwardly from the chisel edge in a vertical plane substantially containing the chisel edge and a longitudinal axis of the screw. |
