Asymmetric Thread Screw for Wood Fiber Penetration
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Solution Overview
Problem
Existing screw designs, such as symmetrical thread screws and those with cutting points, are inefficient and cause fiber tearing during insertion, leading to prolonged installation times and difficulty in disassembly.
Innovation Solution
An asymmetric thread screw with a ballistic point and unique thread configuration, featuring a long slide flank and short grip flank, minimizes fiber cutting by using a conical tip and asymmetrical threads, allowing for penetration without tearing and providing increased gripping strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If symmetrical thread screws with cutting points are used, then the screw can penetrate the material, but it causes fiber tearing and ripping during insertion
Solution Approach 1:
The patent applies asymmetry by designing threads with different flank angles: a shallower lead flank angle (10-20 degrees) that slides along fibers to minimize tearing, and a steeper drag flank angle (60-80 degrees) that provides gripping force. This asymmetric thread configuration allows the screw to penetrate wood fibers smoothly without the ripping and tearing caused by symmetrical threads.
Solution Approach 2:
Instead of using a traditional cutting point that chops through fibers, the patent inverts the approach by using a ballistic point with asymmetric threads that push and slide fibers aside. The thread geometry is inverted from conventional designs, with the load-bearing function transferred to the asymmetric flanks rather than relying on cutting action.
2Strength
If regular nails or glue are used, then strong binding is achieved, but disassembly becomes difficult or impossible
Solution Approach 1:
The patent incorporates a segmented thread design with distinct lead and drag flanks that perform different functions. The asymmetric segmentation allows the screw to achieve strong holding power during insertion while maintaining ease of removal, as the drag flank engages fibers differently during extraction compared to insertion.
Solution Approach 2:
The asymmetric thread configuration creates dynamic interaction with wood fibers during both insertion and removal. During insertion, the shallower lead flank slides fibers aside while the steeper drag flank provides gripping force. During removal, the geometry allows fibers to release more easily, enabling disassembly while maintaining strong initial binding.
3Productivity
If impact driving is used with prior art screw designs, then insertion speed is increased, but the screw rips and tears wood fibers
Solution Approach 1:
The asymmetric thread design with shallower lead flank (10-20 degrees) and steeper drag flank (60-80 degrees) is specifically optimized for impact driving. The asymmetric geometry allows the screw to withstand impact forces while sliding along fibers with minimal tearing, maintaining high insertion efficiency without the fiber damage caused by conventional symmetric thread designs.
Solution Approach 2:
The patent changes critical geometric parameters of the thread, specifically the flank angles and pitch configuration. The lead flank angle is reduced to 10-20 degrees from conventional steeper angles, and the pitch is optimized for impact driving applications. These parameter changes enable the screw to penetrate material efficiently under impact while minimizing fiber rupture and tearing.
Data Source
AI summary
An asymmetric thread impact drivable screw and clip for use with a power impact device for penetrating wood fibers while minimizing cut fibers. The screw includes an impact head and a conical shaped tip having a ballistic insertion angle at the ends of a shank. The shank defines asymmetrical threads with an insertion flank having a long side at a slide angle peaking at a crest supported by a catch flank positioned at a grip angle. Varying tool accepting recess are taught for the head along with multiple thread sections. A mushroom compaction thread section is also taught.