Asymmetrical Wood Screw Thread Design for Chip Management
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Solution Overview
Problem
Conventional screws for wood planks face issues with wood chip expulsion, leading to obstruction, increased operational effort, plank cracking, and lack of anti-pull-out and anti-screw-out properties, resulting in surface damage and instability under vibrations.
Innovation Solution
A screw design featuring a shank with an insertion tip, a head end, and a straight portion with asymmetrical threads and anti-screw-out teeth, which effectively cut wood fibers and provide anti-screw-out properties by guiding and retaining wood chips, ensuring secure embedding and preventing loosening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the end cutting groove extends axially along the shank, then the screw can cut wood fibers effectively, but wood chips cannot be expelled smoothly causing obstruction and increased operational effort
Solution Approach 1:
The end cutting groove is divided into multiple segments (first, second, third cutting grooves) arranged circumferentially around the shank. This segmentation allows wood chips to be channeled through multiple paths simultaneously, improving chip expulsion efficiency while maintaining effective wood fiber cutting capability.
2Productivity
If the screw thread is forward screwed in the plank, then the screw can penetrate the wood easily, but the screw lacks anti-pull-out and anti-screw-out properties causing loosening under vibrations
Solution Approach 1:
The screw thread is designed with asymmetrical thread convolutions where the forward thread convolution has a different profile than the reverse thread convolution. The forward thread has optimized angles for easy penetration, while the reverse thread features enhanced engagement geometry that provides superior anti-pull-out and anti-screw-out properties, preventing loosening under vibrations.
3Ease of operation
If the screw penetrates the plank with standard thread design, then the screw can be installed easily, but the surface flatness of the plank is worsened due to waste chips released from the drilled hole
Solution Approach 1:
The end cutting grooves are specifically designed to extract and remove wood chips from the drilled hole during the screw penetration process. The grooves act as channels that actively evacuate chips from the hole, preventing them from being released onto the plank surface and thereby maintaining surface flatness.
4Ease of manufacture
If the screw uses conventional thread geometry, then the screw can be manufactured simply, but the screw lacks effective bonding and anti-pull-out forces
Solution Approach 1:
The asymmetrical thread convolution design optimizes the thread geometry for dual functionality: the forward thread convolution provides efficient penetration with reduced resistance, while the reverse thread convolution creates enhanced mechanical interlocking with the wood fibers. This asymmetrical geometry increases bonding strength and anti-pull-out resistance without significantly complicating the manufacturing process.
Data Source
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AI summary
A screw (20) includes a shank (22) having an insertion tip (24) and a head end (26) which has an upper portion (50) with a cutting portion (62) and a lower portion (52) from which a plurality of anti-screw-out teeth (54) protrude. Each anti-screw-out tooth (54) includes a guide face (56) and a stop face (58) intersecting a circumferential surface (53) of the lower portion (52) for development of a recessed channel (59). A first thread (36) on the shank (22) includes a plurality of asymmetrical thread convolutions (40) each having a first cutting face (42) facing onto the insertion tip (24) and a second cutting face (44) backing onto the insertion tip (24). The first cutting face (42) and a horizontal axis form an included angle (C1) between 25 and 45 degrees. The second cutting face (44) and the horizontal axis form an included angle (C2) between 3 and 23 degrees. The screw (20) is in favor of surface flatness of a to-be-connected plank and pull-out as well as anti-screw-out properties of the screw (20).