Counterbore Bolt Retention via Polygonal Head and Interlocking Member
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Solution Overview
Problem
Bolts positioned in oversized holes with counterbores are prone to accidental ejection during maintenance or impact, posing risks to workers and machinery due to lack of secure retention without a nut.
Innovation Solution
A fastener system featuring a polygonal bolt head with recesses and a retaining member that overlaps the counterbore, secured by screws, to trap the bolt and prevent rotation, ensuring secure retention without obstructing easy removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the counterbore is oversized to allow easy bolt removal, then the ease of operation is improved, but the reliability of bolt retention deteriorates as the bolt becomes susceptible to accidental ejection
Solution Approach 1:
A retaining member is introduced as an intermediary element between the bolt and the counterbore. This retaining member has a first engagement feature that interfaces with the bolt (such as a slot or groove in the bolt head) and a second engagement feature that interfaces with the counterbore (such as tabs engaging the counterbore wall), thereby providing reliable retention while maintaining the oversized counterbore configuration for easy removal when needed.
2Ease of operation
If the counterbore is oversized to permit limited rotation of the bolt head, then the ease of operation is improved for nut application, but the reliability of preventing full rotation deteriorates
Solution Approach 1:
The retaining member introduces asymmetric engagement features that provide controlled rotational movement in one direction while preventing rotation beyond a certain point. For example, the engagement between the retaining member's tabs and the counterbore wall, combined with the engagement feature on the bolt head, creates a mechanical constraint that allows limited rotation for nut application but prevents the bolt head from rotating enough to pass a corner of the counterbore.
3Reliability
If a retaining mechanism is added to prevent bolt ejection, then the reliability of bolt retention is improved, but the device complexity increases
Solution Approach 1:
The retaining mechanism is segmented into distinct functional components: a retaining member with separate engagement features for the bolt and the counterbore, and optional fastening elements. This segmentation allows each component to perform its specific function independently while maintaining overall simplicity. The retaining member can be a simple bar or plate with slots and tabs, avoiding complex mechanisms while achieving reliable retention.
Data Source
AI summary
A fastener system for retaining a loose elongate fastener in a counterbore, including an elongate fastener, such as a bolt, having a head for being received and retained in a counterbore in a structure and in generally flush relation to a surface of the structure surrounding the counterbore, and a retaining member for being secured to the structure proximate the counterbore and overlapping the counterbore to trap the loose fastener in the counterbore.