Spiral drive fastener with engagement ramp
The fastener of this application is designed to facilitate the insertion of rotating power driven tools into the fastener recess. The recess of this fastener generally uses spirally configured driving surfaces and is formed in a counterbore in the upper surface of the fastener. The driving lobes have upper surfaces that are depressed a distance into the counterbore. A ramp surface is formed on each of the upper surfaces that causes a spinning bit to fall into the recess in an engaged manner. The ramp surfaces are constructed with both removal and installation ramp portions.
1. A recess formed in the top surface of the head of a fastener, said recess comprising:
multiple radially inward extending lobes that define spirally configured driving surfaces, said driving surfaces extending substantially axially, from outward
facing top surfaces of the lobes towards the bottom of the recess, said driving surfaces constructed for engagement with a mating drive tool for rotating said
fastener in installation and removal directions about a longitudinal axis, said recess further comprising:
a substantially cylindrical, axially aligned, counterbore constructed in an upper surface of the fastener head wherein the outward facing top surfaces of said multiple lobes are recessed therein;
a non-driving ramp surface constructed on each of said multiple lobes on the outward facing surfaces thereof, each of said ramp surfaces further comprising:
an installation ramp portion extending radially inward and circumferentially in the installation direction from an apex of said ramp surface, wherein said installation ramp portion declines from the apex at a compound angle both radially and circumferentially; and
a removal ramp portion extending radially inward and circumferentially in the removal direction from the apex of said ramp surface, wherein said removal ramp portion declines from the apex at a compound angle both radially and circumferentially; and
further wherein said installation ramp portion and said removal ramp portion are adapted to urge a rotating drive tool into mating engagement with the drive surfaces in either the installation or removal directions.
2. A recess for a fastener, according to claim 1 , wherein said installation ramp portion forms a sector of said counterbore extending in a first predetermined circumference and said removal ramp portion forms a sector of said counterbore extending in a second predetermined circumference and wherein said first sector circumference is greater than said second sector circumference.
3. A recess for a fastener, according to claim 2 , wherein the ratio of said first sector circumferences to said second sector circumference is substantially 2 to 1.
4. A recess for a fastener, according to claim 2 , wherein said first sector circumference is 60° and said second sector circumference is 30°.
5. A recess for a fastener, according to claim 1 , wherein the installation ramp portion declines circumferentially at a predetermined angle.
6. A recess for a fastener, according to claim 5 , wherein said predetermined angle is in the range of 2° to 6°.
7. A recess for a fastener, according to claim 1 , wherein the removal ramp portion declines circumferentially at a predetermined angle.
8. A recess for a fastener, according to claim 7 , wherein said predetermined angle is in the range of 1° to 2°.