GB491710A - Improvements in and relating to a method of making self-threaded tapping screws or threaded fasteners - Google Patents

Abstract

491,710. Self-tapping screws; rolling. ROSENBERG, H. June 22, 1937, No. 9704 /38. Divided out of 491,680. [Classes 83 (ii), 83 (iii), and 83 (iv)] In a method of making selftapping screws having a tapered entering end with the thread of the tapered part intersected by one or more grooves, the thread and grooves are formed simultaneously by rolling or stamping between dies. The screw has a holding portion 2 with threads of full depth and a tapered entering portion 5 with threads 6 of diminishing height towards the end but uniform core diameter. A groove 7 is formed in the apex of the tapering threads. Longitudinal grooves 8, either axial or inclined, extend from the end of the screw to a point short of the first full thread 2 so as to leave a complete grooved thread 5x between the threads 2 and 5. In a modification, the tapering threads 6a, Fig. 6, remain of V-shaped section and are not grooved at the apex. In a further modification the tapering threads 6b, Fig. 7, are of truncated section and may or may not be grooved at the apex. The grooves 8 have the section shown in Fig. 15 with radial faces 8c to provide cutting edges and rounded shoulders 8d which increase the pressure of the cutting edges on the work, and are of sufficient section to accommodate the cuttings produced. Any number of grooves 8 may be provided, and in a further modification the grooves intersect at least one of the full section threads. The screws may be provided with heads 3b, Fig. 7, of hexagonal or slotted type, or with non- circular recesses 3, Fig. 1, for the reception of a driver of similar section. Rolling.-The screw threads and grooves 8 are produced without removal of material from the screw blanks bv means of a stationary die 25, Fig. 9, of usual screw-forming pattern, and an opposing movable die 26, Figs. 11, and 13, having a screw-forming portion 26a, and a raised notched portion 28 for producing the grooves 8 in the tapered end of the blank. The first few notches 28 are roughened at 29 to grip the blank and are offset below the level of the bases of the grooves 26a, whilst the remaining notches are level with the grooves 26a as shown in Fig. 13. The dies compress the surface of the blanks, which may be case hardened to enable them to be used in metal such as soft iron or steel, and the screws may be used for forming threads to receive other fasteners. The grooves 8 may be formed by stamping or punching before the rolling of the threads.