| 摘要 |
A countersunk screw comprises a screw rod and a countersunk head that has the upper flat surface at the side of which a depression is provided for drive instrument, and the lower surface that is divergent in direction to the screw rod. The lower surface of the head has several arranged uniformly in perimeter cutting elements that have front facets that are arranged in parallel and with side displacement with respect to the long axis of the screw in direction of turning-in, and outer cutting edges that determine the outer conical encircling surface of the head of the screw. Each of cutter elements has a backed-off back angle that is formed by section of a convex conical surface that goes from the cutter edge of the cutter element to the front facet of the next cutting element and determines the width of the front facet of the latter in each secant plane that is normal to the longitudinal axis of the screw. Width of the front facet of each cutter element in cross secant planes increases at displacement from the lower section of the cutter edge of the cutter element to its end upper section. |
