Stick fit fastener recess system
Various embodiments described herein provide a fastener system having straight walled driving surfaces that provides a reliable stick fit feature, while also improving stability of engagement between the system components. A feature of the new system is to allow stick fit engagement of existing standard straight walled drivers in the new system.
1. A fastener, comprising: a head and a shank having a central longitudinal axis, wherein the head is constructed including a recess having a central portion and a plurality of wings radiating outwardly from the central portion, each of the wings having driving surfaces including an installation driving surface and a removal driving surface, separated by a non-driving transition contour, the non-driving transition contour forming a radially inward-most portion of the wing, and wherein the driving surfaces are constructed in substantially parallel alignment with the central longitudinal axis of the fastener; and a wedge formed in the non-driving transition contour of the wings to present a tapered interface surface, wherein the recess is configured to engage in a mating engagement with a corresponding driver bit end having straight drive walls parallel to the longitudinal axis during the mating engagement and a radius at a transition contour greater than a recess inner root radial distance and less than a recess top radial distance and further having a bit end diameter and defining a driver lobe engagement length with each of the driving surfaces of the fastener, wherein a ratio of the driver lobe engagement length to the bit diameter during the mating engagement is greater than 0.11, wherein the mating engagement includes a lowest frictional engagement between the tapered interface surface and a straight-walled transition contour of the driver bit end parallel to the longitudinal axis that is above a bottom of the tapered interface surface and within a lower one third of the recess, and wherein during the mating engagement the driving surfaces of the fastener extend to the lowest frictional engagement, wherein each tapered interface surface is concave, having a radius of curvature greater than a radial distance from the longitudinal axis to the tapered interface surface.
2. The fastener of claim 1 , wherein the fastener is configured such that the ratio of the driver lobe engagement length to the bit diameter during the mating engagement of the fastener with the corresponding driver bit end is from about 0.15 to about 0.21.
3. The fastener of claim 1 , wherein each tapered interface surface is constructed to form a frictional engagement with the driver bit end at two interface regions that are separate from each other.
4. The fastener of claim 3 , wherein the two interface regions are configured to provide more than one frictional surface contact between each interface surface and the driver bit end.
5. The fastener of claim 3 , wherein the two interface regions are at opposed edges of each tapered interface surface.
6. The fastener of claim 3 , wherein the two interface regions are entirely within the lower one third of the recess.
7. The fastener of claim 1 , wherein the recess includes exactly six of the wings.
8. The fastener of claim 1 , wherein the recess includes exactly four of the wings.
9. The fastener of claim 1 , wherein each interface surface is tapered at an angle with respect to the longitudinal axis, wherein the angle is selected from one the following options: (1) in the range of about one half degree (0.5°) to about twelve degrees (12°), (2) in the range of about four degrees (4°) to about eight degrees (8°), (3) about six degrees (6°).
10. A system, comprising:
a fastener including: a head and a shank having a central longitudinal axis, wherein the head is constructed including a recess having a central portion and a plurality of wings radiating outwardly from the central portion, each of the wings having driving surfaces including an installation driving surface and a removal driving surface, separated by a non-driving transition contour, the non-driving transition contour forming a radially inward-most portion of the wing, and wherein the driving surfaces are constructed in substantially parallel alignment with the central longitudinal axis of the fastener; and a wedge formed in the non-driving transition contour of the wings to present a tapered interface surface, wherein the recess is configured to engage in a mating engagement with a corresponding driver bit end having straight drive walls parallel to the longitudinal axis during the mating engagement and a radius at a transition contour greater than a recess inner root radial distance and less than a recess top radial distance and further having a bit end diameter and defining a driver lobe engagement length with each of the driving surfaces of the fastener, wherein a ratio of the driver lobe engagement length to the bit diameter during the mating engagement is greater than 0.11, wherein the mating engagement includes a lowest frictional engagement between the tapered interface surface and a straight-walled transition contour of the driver bit end parallel to the longitudinal axis that is above a bottom of the tapered interface surface and within a lower one third of the recess, and wherein during the mating engagement the driving surfaces of the fastener extend to the lowest frictional engagement; and
a driver including the corresponding driver bit end.
11. A fastener, comprising: a head and a shank having a central longitudinal axis, wherein the head is constructed including a recess having a central portion and a plurality of wings radiating outwardly from the central portion, each of the wings having driving surfaces including an installation driving surface and a removal driving surface, separated by a non-driving transition contour, the non-driving transition contour forming a radially inward-most portion of the wing, and wherein the driving surfaces are constructed in substantially parallel alignment with the central longitudinal axis of the fastener; and a wedge formed in the non-driving transition contour of the wings to present a tapered interface surface, wherein the recess is configured to matingly engage with a corresponding driver bit end such that the driver bit end has a radius at a transition contour greater than a recess inner root radial distance and less than a recess top radial distance, wherein each tapered interface surface is concave, having a radius of curvature greater than a radial distance from the longitudinal axis to the tapered interface surface.