Countersunk Fastener Head Structure for Flush Wood Fastening
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Solution Overview
Problem
Conventional screws fail to achieve a flush fit with workpieces due to unbroken fibers and burrs, leading to poor cutting efficiency and fastening effects, especially when dealing with resilient materials like hardwoods.
Innovation Solution
The fastener design incorporates cutting portions and ribs on the head with accommodation rooms to effectively cut and scrape fibers, a progressive projecting blade to press down burrs, and a threaded portion with varying thread sections and notches to enhance cutting and engagement, ensuring the head lies flush with the workpiece surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional screws with simple head design are used, then the structure is simple and easy to manufacture, but the head cannot fit flush with the workpiece surface due to unbroken fibers and burrs
Solution Approach 1:
The head is segmented into multiple functional zones: a conical portion for initial engagement, a cylindrical portion with cutting portions and cutting ribs for fiber cutting, and accommodation rooms for burr collection. This segmentation allows each zone to perform its specific function, achieving flush fit while managing the complexity through functional division.
Solution Approach 2:
The cutting portions and cutting ribs act as intermediaries between the threaded portion and the workpiece surface. They intermediate the cutting process by severing unbroken fibers and managing burrs, allowing the head to achieve flush fit with the surface without direct contact between the threaded portion and surface fibers.
2Productivity
If spaced apart ribs are used to engage with workpiece, then the structure is simple, but the ribs cannot break fibers into chips completely resulting in poor cutting effect
Solution Approach 1:
The cutting portions and cutting ribs are merged into an integrated system on the head. The cutting portions with projecting blades perform the primary cutting action to create chips, while the cutting ribs provide additional cutting support and fiber management. This merging of functions achieves complete fiber breakdown into chips, significantly improving cutting efficiency despite increased structural complexity.
3Manufacturing precision
If conventional screw design is used, then the manufacturing is simple, but burrs stick out from the surface preventing flush fit and reducing fastening effect
Solution Approach 1:
The accommodation rooms are designed to extract and collect burrs and cut material from the cutting zone. By providing dedicated spaces for burr collection, the design removes the harmful effect of protruding burrs from the workpiece surface, enabling flush fit. This extraction function is integrated into the head structure, balancing manufacturing precision requirements with manufacturing feasibility.
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
This design significantly reduces drilling resistance, enhances cutting efficiency, and improves the fastening effect by ensuring a flush fit and stable engagement with the workpiece, preventing undue fiber entanglement and burr accumulation.
Implementation Method 1
the drilling portion 13 punctures a workpiece 2 with fibers and rotates the head 11 with a tool (not shown), the threads 14 keep drilling into a bore 21 and cut fibers
Implementation Method 2
the cutting portions continue scraping the cut material off to enhance the cutting ability and reduce the drilling resistance
Implementation Method 3
The plurality of cutting ribs project from the bottom face and extend radially between the cutting portions and the shank to be directed at corresponding ones of the plurality of cutting portions
Implementation Method 4
Burrs or a bulge produced during the drilling operation can be fully pressed down by the projecting blade and captured within a bore of the workpiece
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A fastener (3) includes a head (31) with a top face (311) and a conical bottom face (312), and a shank (32) with a threaded portion (34) spiraling thereon and a drilling portion (33). The head (31) includes a plurality of cutting portions (313) and cutting ribs (314) formed on the bottom face (312) to thereby cut and shave fibers and accommodate chips. Each cutting portion (313) extends towards the shank (32) and includes a projecting blade (3131) formed circumferentially of the top face (311), and an adjoining wall (3132) and a flank wall (3133) respectively connected to the projecting blade (3131) and meeting at a cutting edge (3134). The cutting ribs (314) extend radially relative to the shank (32) . The cutting portions (313) and the cutting ribs (314) cooperate to continue cutting and press remnants and the bulge down so that the head (31) fits flush with the surface of the workpiece (4) to thereby increase the evenness and the fastening effect after the head (31) is fastened in position.