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 fastener system comprising:
a fastener constructed with a head and a shank, said shank having a longitudinal axis, and said head constructed having a recess formed at its end, wherein said recess comprises:
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;
a non-driving transition surface 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 surface extending radially inward into the central portion, said surface being tapered from a first distance from the longitudinal axis at a top portion thereof to a second distance from said longitudinal axis at a bottom portion thereof, wherein said first distance is larger than said second distance;
a driver constructed with driving surfaces shaped to engage the installation and removal walls of the recess, said driver having non-driving surfaces constructed in grooves between said driving surfaces; and
further wherein said interference contours of said transition surfaces of said recess cooperate to form an interference fit with the non-driving surfaces in the grooves of the driver.
2. The fastener, according to claim 1 , wherein said interference surface forms an angle with a line parallel to said longitudinal axis in a range of between 0.5degrees to 2 degrees.
3. The fastener, according to claim 1 , wherein said interference surfaces are constructed to provide an interference fit only at a forward portion of said driver and to allow said driver to have a surface to surface contact with said wings at a rearward portion of said driver.
4. The fastener, according to claim 1 , wherein said first distance is constructed substantially according to a standard recess opening of a spiral type recess.