Fastener Recess Geometry for Stable Stick-Fit Driver Alignment

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Solution Overview

Problem

Existing straight walled fastener systems face challenges with axial misalignment, unreliable friction engagement, and premature disengagement due to localized high stresses, especially under high torque conditions, which can lead to deformation and failure.

Innovation Solution

A fastener system with a recess having tapered interface surfaces and a driver with matching lobes, where the installation and removal surfaces are separated by a transition contour, providing a wedge-shaped interface to enhance stability and frictional engagement, allowing for a reliable stick fit and improved axial alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If straight walled recesses are used for driver engagement, then manufacturing is simplified and head strength is maintained, but axial misalignment and unreliable friction engagement occur leading to premature disengagement

Engineering Contradiction:

Improverecess manufacturing simplicityVSAvoiddriver-recess engagement reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The recess incorporates localized tapered interface surfaces at specific regions where friction engagement is needed, while maintaining straight walled driving surfaces for torque transmission. This localized modification provides reliable friction engagement without complicating overall recess manufacturing or compromising head strength.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The tapered interface surfaces introduce a controlled curvature element to the otherwise straight walled recess. This curvature creates the friction engagement needed for reliable driver-recess connection while maintaining the predominantly straight geometry for ease of manufacture and head strength.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Ease of operation

If clearance is provided between driver and recess for insertion, then driver insertion is enabled, but face-to-face contact is reduced resulting in localized high stresses

Engineering Contradiction:

Improvedriver insertion easeVSAvoidlocalized stress concentration

Core Design Contradiction:

Ease of operationVSStress or pressure

Solution Approach 1:

The tapered interface surfaces create preliminary friction engagement as the driver enters the recess, establishing face-to-face contact before full torque application. This preliminary action distributes stresses uniformly across the interface rather than concentrating them at discrete points.

Inventive Principle:

Principle #10Preliminary action

3Stress or pressure

If face-to-face contact is achieved between driver and recess, then stress distribution is improved, but cam-out resistance is reduced under high torque conditions

Engineering Contradiction:

Improvestress distribution uniformityVSAvoidcam-out tendency

Core Design Contradiction:

Stress or pressureVSObject-affected harmful factors

Solution Approach 1:

The recess features localized tapered interface surfaces at specific regions for friction engagement, while maintaining straight walled driving surfaces for torque transmission. This differentiation allows face-to-face contact for stress distribution without creating the continuous angled surfaces that would cause cam-out.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The recess is segmented into distinct functional zones: tapered interface surfaces for friction engagement and stress distribution, and straight walled sections for torque transmission and cam-out resistance. This segmentation allows each zone to optimize its specific function without compromising the other.

Inventive Principle:

Principle #1Segmentation

4Stability of the object's composition

If friction engagement is increased for stick fit, then axial alignment stability is improved, but driver insertion difficulty increases

Engineering Contradiction:

Improveaxial alignment stabilityVSAvoiddriver insertion ease

Core Design Contradiction:

Stability of the object's compositionVSEase of operation

Solution Approach 1:

The tapered interface surfaces provide friction engagement only in specific angular regions, changing the friction parameter locally rather than throughout the entire driver-recess interface. This allows sufficient friction for axial alignment stability without creating excessive resistance to driver insertion.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The system achieves enhanced stability and reduced risk of cam-out, enabling reliable engagement and disengagement, even under high torque conditions, and improved compatibility with standard drivers, while maintaining the effectiveness of driver-recess engagement.

Implementation Method 1

the recess and driver interface surfaces are constructed to form a frictional engagement when the fastener head and driver bit end are in the mated engagement

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS10995788B2Stick fit fastener recess system

Publication Date: 2021.05.04 PHILLIPS SCREW CO

AI summary

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.