Self-Tapping Screw Cutting Edges for Lower Anchor Insertion Torque
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Solution Overview
Problem
Existing self-tapping screws are not equally suitable for screwing into wood and plastic expansion plugs, as they often require pre-drilling and face high torque due to friction, especially when the screw shank diameter exceeds the anchor hole diameter.
Innovation Solution
A self-tapping screw design featuring a conical screw tip with cutting edges that extend at an angle to the screw thread, capable of cutting a core hole matching the screw shank diameter, reducing friction and torque by creating a hole that is not larger than the screw shank, and optionally featuring a threadless section and varying thread cross-sections for efficient material displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the screw shank diameter is increased to provide better fastening strength, then the fastening strength is improved, but the friction and torque increase significantly making it difficult to screw into pre-drilled holes
Solution Approach 1:
The screw is divided into functionally distinct sections: a threadless shank portion for insertion through the pre-drilled hole with minimal friction, and a threaded portion for engaging the anchor base. This segmentation allows the screw to overcome the torque-friction contradiction by separating the insertion function from the fastening function.
Solution Approach 2:
The screw design anticipates the insertion requirement by providing a threadless shank portion that fits into a pre-drilled hole. This preliminary preparation of the insertion path eliminates the need for the threaded portion to cut through the material during insertion, thereby reducing friction and torque requirements.
2Ease of manufacture
If cutting edges extend radially beyond the screw shank to cut a larger pilot hole, then the pilot hole is easier to form, but the hole diameter becomes larger than the screw shank causing loss of expansion effect in plastic anchors
Solution Approach 1:
The cutting edges are positioned to extend radially beyond the screw shank only in the front thread section, not along the entire screw length. This localized cutting action allows the front portion to efficiently form the pilot hole while the threadless shank portion maintains precise control over the final hole diameter to match the screw shank diameter exactly.
Solution Approach 2:
The cutting edges perform a partial cutting action only in the front thread section rather than along the entire screw length. This partial action is sufficient to form the pilot hole without over-cutting, and the subsequent threadless shank portion ensures the final hole diameter is precisely controlled to match the screw shank diameter.
3Strength
If the screw thread extends over the entire screw shank length, then the fastening engagement is maximized, but the torque required for insertion increases due to friction along the entire length
Solution Approach 1:
The screw thread is segmented to exist only in the rear portion of the screw shank, leaving the front portion threadless. This segmentation allows the threaded portion to provide maximum fastening engagement while the threadless portion minimizes friction during insertion through the pre-drilled hole.
Solution Approach 2:
The threadless shank portion performs the preliminary action of inserting the screw through the pre-drilled hole with minimal friction. This preliminary insertion prepares the path for the threaded portion to then engage the anchor base, separating the high-friction fastening engagement from the low-friction insertion process.
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
The screw effectively reduces the torque required for screwing into wood or plastic by cutting a core hole that matches the screw shank diameter, minimizing friction and ensuring the screw can spread plastic expansion plugs without enlarging the hole excessively.
Implementation Method 1
The at least one cutting edge is directed opposite to the screw insertion direction and performs a cutting motion when the screw is screwed into an anchor base
Implementation Method 2
a screw thread, which can be single-start or multi-start and which extends from the screw tip at least over a portion of the length of the screw shank
Data Source
Figure 1~2
AI summary
The invention relates to a self-tapping screw (1) having a screw shaft (2), a screw tip (3) and a triangular thread as a screw thread (5). The invention proposes to provide the screw shaft (2) in a short section (L) adjoining the screw tip (3) with cutting edges (6) on a diameter of the screw shaft (2) by means of helical- and sawtooth-shaped grooves (7).