Sickle Tip Self-Tapping Screw for Wood Splitting Reduction
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Solution Overview
Problem
Existing self-drilling screws are not suitable for use in wood, as they often cause splitting and require pre-drilling, resulting in low pull-out strength and high forming torque, and are difficult to produce.
Innovation Solution
A self-drilling screw design featuring a sickle point with a main cutting edge parallel to the screw axis and a secondary cutting edge extending obliquely, allowing the screw to drill a hole with the core diameter of its thread while reducing splitting and requiring lower forming torque, by using a sickle tip with a main cutting edge that cuts radially and a secondary cutting edge that cuts axially.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional self-drilling screw with an off-center drill bit is used, then the screw can drill through sheet metal, but it causes the screw tip to run out during drilling and produces poor screw connections with low pull-out strength
Solution Approach 1:
The patent applies asymmetry by positioning the drill bit off-center relative to the screw axis. The drill bit is arranged such that its axis is offset from the screw axis, creating an asymmetric configuration that allows the drill bit to self-center during drilling while the screw threads engage properly. This asymmetric design resolves the contradiction by enabling both stable drilling and reliable screw connection.
Solution Approach 2:
The patent applies preliminary action by designing the drill bit with a specific geometry and positioning that prepares it to automatically center itself during the drilling process. The drill bit's initial off-center position is deliberately designed to create self-centering action as drilling progresses, eliminating the need for pre-punching or alignment fixtures and ensuring stable drilling from the start.
2Ease of operation
If a standard wood screw is used, then the screw can be screwed into wood, but it causes wood splitting and requires pre-drilling, resulting in high forming torque
Solution Approach 1:
The patent applies segmentation by dividing the screw into distinct functional zones: a drill bit portion for creating the hole and a threaded shank for engagement. The drill bit is separated from the threaded portion, allowing it to perform the drilling function while the threads perform the engagement function. This segmentation enables the screw to drill its own hole without causing splitting while maintaining easy screwing operation.
Solution Approach 2:
The patent applies inversion by reversing the conventional sequence of operations. Instead of pre-drilling a hole and then inserting a screw, the screw itself performs the drilling operation first through its integrated drill bit, then automatically transitions to thread engagement. This inverted approach eliminates the need for separate pre-drilling steps and prevents wood splitting.
3Reliability
If existing self-drilling screws are used for wood, then drilling can be performed, but the screws require pre-drilling and produce low pull-out strength with high forming torque
Solution Approach 1:
The patent applies merging by combining the drill bit and threaded shank into a single integrated screw component. The drill bit and threads are formed as one continuous piece, eliminating the need for separate drilling and screwing operations. This merging increases pull-out strength by ensuring proper hole preparation and thread engagement in one step, while the integrated design actually simplifies production compared to multi-component systems.
Data Source
Figure 1a~1d
Figure 2a~2d
Figure 3a~3d
AI summary
A self-tapping screw is described with a drilling part and a shaft (14) which is provided with a thread (12) and a core diameter (Dk). The drilling part has a drilling tip (20) which is arranged eccentrically in relation to a longitudinal axis of the screw, and is configured as a sickle tip (101) which has a primary cutting edge (30) and a secondary cutting edge (40). The primary cutting edge (30) is formed by the intersection of a cutting surface (60) and a main free surface (90) and extends from the drilling tip (20) parallel to the longitudinal axis of the screw. The secondary cutting edge (40) is formed by the intersection of the cutting surface (60) and an auxiliary free surface (70) and extends obliquely with respect to the longitudinal axis of the screw over the width of the drilling part. A hole with the core diameter (Dk) can be produced by way of the screw, into which the thread (12) cuts a counterthread. As a result of the joint action of the primary and secondary cutting edges (30, 40), the fibres are severed during the drilling operation when a workpiece is made from wood, so that the screw develops practically no splitting action.