Fastener Recess Geometry for Full-Surface Bit Contact
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Solution Overview
Problem
Conventional drive systems for fasteners often result in high surface contact stresses due to point, line, or area contact patterns, leading to bit failure, premature wear, and damage to the fastener finish, especially as reaction torque increases, causing elastic distortion and potential recess failure.
Innovation Solution
A drive system featuring a fastener with a recess and a bit, both having drive surfaces formed of polygon involutes with continuous tangent arcs, where each arc has a constant but different radius, maximizing full surface contact and minimizing stress by maintaining a consistent gap during rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional drive system geometries (point, line, or area contact) are used, then the bit can be inserted into the recess, but high surface contact stresses occur leading to bit failure, premature wear, and damage to the fastener finish
Solution Approach 1:
The drive surfaces of both the bit and recess are formed with polygon involute geometry comprising continuous tangent arcs. This curved surface design allows the bit to maintain full surface contact with the recess during rotation, distributing contact stresses across the entire drive surface area rather than concentrating them at points or lines, thereby reducing peak stresses and preventing bit failure and fastener damage
Solution Approach 2:
The invention changes the geometric parameters of the drive surfaces by using polygon involutes with specific radius relationships. The bit drive surface and recess drive surface are designed with matching curvature radii that maintain a consistent gap throughout rotation, ensuring full surface contact and optimal stress distribution across the interface
2Stress or pressure
If area contact surface pattern is used, then contact stress is reduced compared to point or line contact, but as reaction torque increases the bit geometry is elastically distorted causing the contact surface pattern to shift from the end of the bit toward the top of the recess, decreasing contact area and increasing contact stresses
Solution Approach 1:
The polygon involute geometry with continuous tangent arcs provides curved drive surfaces that maintain full surface contact under varying torque conditions. The specific radius relationships between bit and recess surfaces ensure that elastic distortion under load does not cause contact pattern degradation, as the curved geometry naturally accommodates deformation while maintaining surface-to-surface contact
Solution Approach 2:
The drive system uses matching polygon involute geometries on both the bit and recess surfaces, creating a composite interface where the two surfaces work together as an integrated system. This matched geometry ensures that under reaction torque, both surfaces deform in a coordinated manner that maintains full surface contact and stable contact pressure distribution
3Ease of operation
If the bit is rotated to initial contact with the recess, then drive engagement is achieved, but point or line contact patterns result in high stresses throughout the drive system
Solution Approach 1:
The curved polygon involute surfaces of the bit and recess are designed to naturally guide the bit into full surface contact during the engagement process. As the bit is rotated into the recess, the continuous tangent arcs ensure that contact begins across the full surface area rather than at discrete points or lines, immediately distributing stresses and enabling smooth drive engagement without stress concentration
Data Source
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AI summary
A drive system with full surface drive contact. The drive system tends to maximize the surface contact pattern or area at typical bit-recess reaction (drive) torque values, thereby tending to minimize bit-recess surface contact stresses, coating damage, recess ream and premature bit fatigue failure. An object of an embodiment of the present invention is to provide a drive system with full surface drive contact. An object of an embodiment of the present invention is to provide a drive system that tends to maximize the surface contact pattern or area at typical bit-recess reaction (drive) torque values, thereby tending to minimize bit-recess surface contact stresses, coating damage, recess ream and premature bit fatigue failure.