Captive Screw Retaining Device for Oblong Holes
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Solution Overview
Problem
Existing fastening assemblies struggle to retain screws with a specific threaded outer diameter in non-modifiable oblong holes of one element while allowing them to be screwed into non-modifiable threaded holes of another element, while also preventing accidental loss of assembly components.
Innovation Solution
A retaining device comprising two parts that can be assembled around a screw, featuring diametrically opposite outer flats allowing the device to fit through oblong holes and reduce radial thickness, with latching means to secure the parts together irreversibly, ensuring the screw can engage with threaded holes without modifying the holes, and providing a mechanism to prevent accidental disassembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a retaining device is used to hold a screw captive in an oblong hole, then the screw is prevented from being lost, but the threaded outer diameter of the screw must be reduced which prevents it from being screwed into pre-existing threaded holes
Solution Approach 1:
The retaining device is divided into two separate parts: a first part that receives the screw shank and a second part that provides the threaded bore. This segmentation allows each part to be independently designed and assembled around the screw, enabling the screw to maintain its full threaded outer diameter while still being retained captive in the oblong hole.
Solution Approach 2:
The first part and second part are assembled together by nesting them in sequence around the screw - the first part is inserted through the oblong hole, then the second part is assembled to the first part, creating a nested structure that secures the screw without reducing its diameter.
2Adaptability or versatility
If the oblong hole is enlarged to accommodate a screw with sufficient threaded outer diameter, then the screw can be screwed into the threaded hole, but the cover must be removable and handleable for re-machining which is often impossible
Solution Approach 1:
The retaining device is designed to be assembled in its final configuration around the screw before being installed in the oblong hole. This preliminary assembly allows the device to be fitted into the existing hole without requiring any enlargement or re-machining of the cover.
Solution Approach 2:
The retaining device acts as an intermediary component between the screw and the oblong hole. Instead of modifying the hole to fit the screw, the retaining device is introduced as a mediator that adapts the existing hole to accommodate the screw with its full threaded diameter.
3Ease of operation
If the first and second parts of the retaining device can be easily assembled, then assembly is simple and quick, but the assembly could be accidentally dismantled allowing loss of components
Solution Approach 1:
The securing means employs a dynamic latching mechanism with a movable latch element that can be engaged or disengaged. During assembly, the latch is easily engaged to secure the parts together, but once engaged, the dynamic nature of the latch prevents accidental disassembly while still allowing intentional dismantling when needed.
Solution Approach 2:
The latching mechanism is designed to be self-securing - once the first and second parts are assembled together, the securing means automatically engages to lock them in place without requiring additional fastening operations. The mechanism itself provides the locking action that prevents accidental dismantling.
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The device (1) has two pieces (5, 6) reamed in a traversing manner along a longitudinal direction (III-III) to receive a rod of a screw (2), where the pieces are assembled on one another and on both sides of a wall (4) by respectively coming near the wall along two support units at support faces (5a, 6a), respectively. A longitudinal section (7) comprises two diametrically opposite external flat spots (9a) for allowing a passage of the longitudinal section in an oblong crossing hole (3).