Spiral drive fastener with friction engageable surface
Interference surfaces are constructed on inner transition surfaces between wings of a fastener having a spiral recess. A portion of the transition surface is tapered to provide the interference. A standard driver for a spiral recess will engage the interference surface to create a “stick fit” engagement. The punch is formed using a wire EDM operation to construct tapered surfaces within the die cavity of a hob. The hob is machined down to obtain the desired depth, which is measured up from a gage spot indicative of the sticking point.
1. A method of manufacturing a fastener said fastener having a shank and a head, said method comprising:
constructing a cylindrical steel blank having a predetermined length;
drilling an axial bore from a top to a bottom of said blank;
inserting a wire through said bore for providing an EDM operation and machining said recess using said wire EDM operation to form a die cavity, wherein said die cavity is constructed having a central portion and a plurality of wings radiating outwardly from the central portion, each of the wings having an installation wall and a removal wall, and further wherein, in said machining operation, transition surfaces are constructed extending between each of the installation and removal walls of adjacent wings, at the radially inner most extent of said wings, each of said transition surfaces formed having an interference contour extending radially inward into the central portion, said contour being tapered from a first radial distance from the longitudinal axis at a top portion thereof to a second radial distance from said longitudinal axis at a bottom portion thereof; and wherein said first radial distance is larger than said second radial distance
hardening said blank to form a hob and forming a punch using said hob; and
forming a recess on the head of the fastener by using said punch.
2. A method of manufacturing a fastener, according to claim 1 , wherein said interference surface is constructed to form an angle with a line parallel to said longitudinal axis in a range of between 0.5 degrees to 2 degrees.
3. A method of manufacturing a fastener, according to claim 1 , wherein said cavity is formed having transition surfaces diametrically opposed across said cavity and said interference surfaces on said opposing transition surfaces are constructed to cooperate to form an interference fit with a driver constructed to engage said fastener.
4. A method of manufacturing a fastener according to claim 1 further comprising determining a level in said recess where an interference fit will occur between a driver and said cavity, measuring a predetermined depth of said recess from said level where said interference occurs, and machining the top of said blank so that the cavity has said predetermined depth.
5. A fastener manufactured according to the method of claim 1 .
6. A method of manufacturing a hob for constructing a tool used for forming a recess in a fastener, said method comprising:
constructing a cylindrical steel blank having a predetermined length;
drilling an axial bore from a top to a bottom of said blank;
inserting a wire through said bore for providing an EDM operation and machining said recess using said wire EDM operation to form a die cavity, wherein said die cavity is constructed having a central portion and a plurality of wings radiating outwardly from the central portion, each of the wings having an installation wall and a removal wall, and further wherein, in said machining operation, transition surfaces are constructed extending between each of the installation and removal walls of adjacent wings, at the radially inner most extent of said wings, each of said transition surfaces formed having an interference contour extending radially inward into the central portion, said contour being tapered from a first radial distance from the longitudinal axis at a top portion thereof to a second radial distance from said longitudinal axis at a bottom portion thereof; and wherein said first radial distance is larger than said second radial distance
hardening said blank to form a hob.
7. A method of manufacturing a fastener according to claim 6 further comprising determining a level in said recess where an interference fit will occur between a driver and said cavity, measuring a predetermined depth of said recess from said level where said interference occurs, and machining the top of said blank so that the cavity has said predetermined depth.
8. A hob constructed according to the method of claim 6 .
9. A method of manufacturing a punch for forming a recess in a fastener said fastener having a shank and a head, said method comprising:
constructing a cylindrical steel blank haying a predetermined length;
drilling an axial bore from a top to a bottom of said blank;
inserting a wire through said bore for providing an EDM operation and machining said recess using said wire EDM operation to form a die cavity, wherein said die cavity is constructed having a central portion and a plurality of wings radiating outwardly from the central portion, each of the wings having an installation wall and a removal wall, and further wherein, in said machining operation, transition surfaces are constructed extending between each of the installation and removal walls of adjacent wings, at the radially inner most extent of said wings, each of said transition surfaces formed having an interference contour extending radially inward into the central portion, said contour being tapered from a first radial distance from the longitudinal axis at a top portion thereof to a second radial distance from said longitudinal axis at a bottom portion thereof; and wherein said first radial distance is larger than said second radial distance
hardening said blank to form a hob and forming a punch using said hob.
10. A method of manufacturing a fastener according to claim 9 further comprising determining a level in said recess where an interference fit will occur between a driver and said cavity, measuring a predetermined depth of said recess from said level where said interference occurs, and machining the top of said blank so that the cavity has said predetermined depth.
11. A punch manufactured according to the method of claim 9 .