Method and apparatus for making a self-thread creating fastener
OwnerDonald R. Veldmaninventor
Life of this patent
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Abstract
A thread forming screw having a helical thread and a tapered lead-in section with a polygonal cross section is formed from a conventional blank by rolling the blank between a pair of thread rolling dies having means thereon to form alternating convex lobes and concave relief areas in the frusto-conical surface of the blank. Thus, the screw may be formed with a polygonally shaped threading end without a prior working of the blank's frusto-conical surface. Curved ramp surfaces smoothly interface the lobes and concavities to allow metal in a workpiece being threaded to roll into the concavities thereby reducing the torque needed to form a thread in the workpiece.
Claims13
A method of manufacturing a thread forming screw having a frusto-conical lead-in section having a tapered surface with lobes thereon and with a polygonal cross section and having a helical thread on a straight shank section comprising the steps of:
- forming the polygonal cross section on said tapered lead-in section by rolling the tapered surface between a pair of thread rolling dies to force metal outwardly from the tapered surface to leave concavities therein and to force the displaced metal from the concavities radially outwardly and circumferentially into upwardly projecting thread forming lobes to provide alternating thread forming lobes projecting above the formerly tapered surface and inwardly extending cavities extending radially inwardly of said formerly tapered surface, and rolling a screw thread on said straight shank during the same rolling operation that rolls said polygonal cross section on said frusto-conical lead-in section.
In an apparatus for manufacturing a thread forming screw from a blank having a cylindrical shank and a frusto-conically shaped lead-in section having a tapered surface at one end of said shank, said apparatus having a pair of thread rolling dies having rolling surfaces thereon for forming a helical thread on said straight shank;
- an improvement comprising means on said rolling dies for forcing metal from said tapered surface section radially outwardly to form concavities therein and to force metal from said concavities radially outwardly into projecting lobes alternating with said concavities to provide a polygonal cross section for said tapered lead-in section with lobes thereon.
Dependencies are inferred from the claim text.