Method of making a thread forming screw

Claim 1

A method of making a thread forming screw of penta-lobular cross-section having a straight main shank portion and a tapered work entering end portion and an intermediate radially enlarged sizing portion comprising: a. providing a headed blank having a straight shank of uniform cross-sectional shape and size from the head to the tip of the shank and which cross-section has a pentalobular configuration with five equi-angularly spaced lobes and five generally flat sides each extending between adjacent lobes and disposed inwardly of a circular locus through the apices of the lobes, b. rolling a main portion of the shank intermediate the head and the work entering end portion on a centerless basis between opposed straight thread forming die surfaces which are thread grooved oblique to the shank axis to form a helical thread thereon, and maintaining the roots of the thread grooves in the straight thread forming die surfaces, where they are adapted to roll the thread to the final shape, in planes parallel to each other and spaced apart a distance such that the crests of the threads rolled on the lobes of the main shank portion do not fill the roots of the thread grooves in the straight thread forming die surfaces whereby to form a helical thread on the main shank portion having a uniform penta-lobular cross-sectional configuration throughout the main shank portion with incompletely finished crests at the lobes, c. while rolling the main shank portion between the straight thread forming die surfaces simultaneously rolling the work entering end portion of the shank on a centerless basis between opposed taper thread forming die surfaces thread grooved obliquely to the shank axis to join with thread grooves in a respective straight die surface, the roots of which thread grooves in the taper thread forming die surface, where they are adapted to roll the thread to the final shape, being disposed in planes that converge in a direction lengthwise to the shank toward the shank axis to roll a thread of pentalobular cross-sectional configuration on the work entering end portion having finished crests at the lobes that taper inwardly, displacing material from the work entering end portion of the shank toward the juncture of the straight and taper thread forming die surfaces to thereby more completely fill the roots of the thread grooves in that region and form at least one sizing turn of penta-lobular cross-sectional configuration at the juncture of the main and work entering end portions having crests at the lobes and sides which are respectively more completely finished and of greater radial height than the crest at the lobes and sides of the main shank portion.

Claim 2

A method of making a thread forming screw of penta-lobular cross-section having a straight main shank portion and a tapered work entering end portion and an intermediate radially enlarged sizing portion comprising: a. providing a headed blank having a straight shank of uniform cross-sectional shape and size from the head to the tip of the shank and which cross-section has a pentalobular configuration with five equi-angularly spaced lobes and five generally flat sides each extending between adjacent lobes and disposed inwardly of a circular locus through the apices of the lobes, b. rolling a main portion of the shank intermediate the head and the work entering end portion on a centerless basis between opposed straight thread forming die surfaces which are thread grooved oblique to the shank axis to form a helical thread thereon, and maintaining the roots of the thread grooves in the straight thread forming die surfaces, where they are adapted to roll the thread to the final shape, in planes parallel to each other and spaced apart a distance such that the crests of the threads rolled on the lobes of the main shank portion do not fill the roots of the thread grooves in the straight thread forming die surfaces whereby to form a helical thread on the main shank portion having a uniform penta-lobular cross-sectional configuration throughout the main shank portion with incompletely finished crests at the lobes, c. while rolling the main shank portion between the straight thread forming die surfaces simultaneously rolling the work entering end portion of the shank on a centerless basis between opposed taper thread forming die surfaces thread grooved obliquely to the shank axis to join with thread grooves in a respective straight die surface, the roots of which thread grooves in the taper thread forming die surface, where they are adapted to roll the thread to the final shape, being disposed in planes that converge in a direction lengthwise to the shank toward the shank axis to roll a thread of pentalobular cross-sectional configuration on the work entering end portion having finished crests at the lobes that taper inwardly, displacing material from the work entering end portion of the shank toward the juncture of the straight and taper thread forming die surfaces to thereby more completely fill the roots of the thread grooves in that region and form at least one sizing turn of penta-lobular cross-sectional configuration at the juncture of the main and work entering end portions having crests at the lobes and sides which are respectively more completely finished and of greater radial height than the crest at the lobes and sides of the main shank portion.