GB1304605A - - Google Patents

Abstract

1304605 Thread rolling screws and taps STANDARD PRESSED STEEL CO 15 May 1970 23536/70 Heading B3N A thread rolling screw fastener comprises a shank having a pilot end 28, the pilot end has a plurality of thread rolling protrusions, e.g. 30, 32, which rise from and fall back to the pilot diameter. Preferably there are two pairs of protrusions, each pair being spaced apart an integral multiple of the pitch of the thread to be rolled; the protrusions of each pair are diametrically oppositely disposed on the pilot end and each is co-extensive with the lead and pitch of the thread to be rolled. A protrusion can cover an angle of arc between 70 and 150 degrees. Protrusions 32, 32a extend further radially than protrusions 30, 30a and provide the final shape of rolled thread. Due to the elasticity of the metal being formed the protrusions may initially roll a thread having a root diameter greater than required. This also provides a self-retaining feature so that a fastener cannot be removed from the threaded hole. The final thread form may be made to give a free running fit between the threads of a fastener or, an interference fit, the latter giving another self-retaining feature. Protrusion 32a has an additional inclined surface 58 which effects the final displacement of wall material to form the final thread root clearance so that the crest thickness of the threads of the fastener fit freely therein. The pilot end may include a knurled facing, Fig. 18 (not shown), to remove any surface coating in a hole ready for the thread rolling. The pilot end may be a plain cylinder with the protrusions thereon, Fig. 17 (not shown). A cupped indentation 31 is formed in the end of the fastener member to define a thin edged cutting ridge 33 which can be used as a punch to form a hole in sheet material that can then have a thread rolled therein.