Abstract A blank is formed for providing a self-thread forming threaded fastener having a straight thread on a shank of circular cross section and tapered thread of the work-entering end. The tapered portion of the thread is of lobular root, pitch and crest surface cross sections and which lobular configuration is continued, but to a diminishing extent, on the first few threads on the shank immediately adjacent to the tapered section. The fastener is formed by rolling between thread-rolling dies a blank having a cylindrical shank of circular cross section and an end section of arcuate lobular cross section including a tapered portion. At least the lobular and tapered portions of the blank are intermittently deflected first in one direction and then in the opposite direction by the dies. Due to such deflections of the end of the blank, a lobular tapered thread is produced on the tapered portion of the blank.
A blank for making a thread-forming screw fastener comprising a cylindrical shank portion, a head at one end of the shank, a cylindrical lead portion at the other end of the shank having a diameter smaller than the diameter of the shank portion, and an intermediate portion diverging from the lead portion to the shank portion in a substantially conical configuration, the axis of a cone circumscribing the intermediate portion being offset from and parallel with the axis of the lead portion whereby the intermediate portion and the lead portion are eccentric relative to one another to provide a lobe on a portion of the periphery of the intermediate portion, the intermediate portion and the lead portion intersecting along a line which extends at an acute angle with respect to the axis of the lead portion whereby all planes transverse to the axis of the lead portion and extending through said line intersect both the lead portion and the intermediate portion.
Claim 2
Dependent Claim
161 words
A blank for making a thread-forming screw fastener comprising a cylindrical shank portion, a head at one end of the shank, a cylindrical lead portion at the other end of the shank having a diameter smaller than the diameter of the shank portion, and an intermediate portion diverging from the lead portion to the shank portion in a substantially conical configuration, the axis of a cone circumscribing the intermediate portion being offset from and parallel with the axis of the lead portion whereby the intermediate portion and the lead portion are eccentric relative to one another to provide a lobe on a portion of the periphery of the intermediate portion, the intermediate portion and the lead portion intersecting along a line which extends at an acute angle with respect to the axis of the lead portion whereby all planes transverse to the axis of the lead portion and extending through said line intersect both the lead portion and the intermediate portion.
Claim 3
Dependent Claim
16 words
The blank of claim 1 in which the intermediate portion has substantially elliptical transverse cross sections.
Claim 4
Dependent Claim
16 words
The blank of claim 1 in which the intermediate portion has substantially oval transverse cross sections.