Countersunk Screw Head Recess Geometry for Stronger Cutting
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Solution Overview
Problem
The existing self-tapping screw head structure has a weak cutting force when driven into a workpiece due to limited cutting ends, requiring high torque and resulting in uneven surfaces from expelled wood crumbs.
Innovation Solution
A screw head design with multiple recesses on the cone portion that cut in both longitudinal and radial directions, accommodating waste and providing overlapping cutting edges for enhanced countersinking and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional self-tapping screw head structure with limited cutting ends is used, then the structure is simple, but the cutting force on the workpiece is weak
Solution Approach 1:
The screw head structure is segmented into multiple cutting ends arranged circumferentially around the longitudinal axis. Each cutting end acts as an independent cutting element, collectively providing enhanced cutting force while maintaining a compact overall structure. The segmentation of the cutting function across multiple ends resolves the contradiction between force and structural simplicity.
Solution Approach 2:
The cutting ends are arranged in a circumferential direction around the longitudinal axis, transitioning from a single-point cutting approach to a multi-point distributed cutting approach. This spatial arrangement in another dimension (circumferential distribution) increases the total cutting force without significantly increasing the longitudinal length of the screw, thus resolving the force-complexity contradiction.
2Force
If high torque is applied to compensate for weak cutting force, then the cutting force becomes sufficient, but the driving speed becomes slow
Solution Approach 1:
By segmenting the cutting function into multiple cutting ends distributed circumferentially, the total cutting force is distributed across multiple contact points with the workpiece. This segmentation allows for more efficient torque utilization, reducing the need for excessively high torque application and thereby improving driving speed without sacrificing cutting force effectiveness.
Solution Approach 2:
The multiple cutting ends are pre-positioned circumferentially around the screw head, ready to engage the workpiece simultaneously or in sequence. This preliminary arrangement of cutting elements ensures that cutting action begins immediately upon engagement, eliminating the need for high torque to overcome initial resistance, thus improving driving speed while maintaining sufficient cutting force.
3Reliability
If multiple recesses with different recess depths are designed on the first cone portion, then the cutting force and stability are improved, but the manufacturing complexity increases
Solution Approach 1:
The first cone portion is segmented into multiple recesses with different recess depths, creating zones for different functions (e.g., chip accumulation, material removal, structural support). This segmentation improves fastening stability by optimizing the interaction between the screw and workpiece, while the systematic arrangement of recesses follows manufacturable patterns that mitigate the increase in manufacturing complexity.
Solution Approach 2:
Different regions of the first cone portion are given different local qualities through varying recess depths. Some areas have deeper recesses for chip accumulation, while others have shallower recesses for structural support or material removal. This local differentiation improves fastening stability by optimizing each region's function, while the overall design remains manufacturable through standardized machining processes.
4Force
If cutting ends are extended to cover a partial circumferential surface, then the cutting force distribution is improved, but the wood crumbs are squeezed outward and remain on the workpiece surface
Solution Approach 1:
The harmful factor (wood crumbs) is extracted from the workpiece surface by designing recesses that capture and contain chips during the cutting process. The recesses act as chip traps, removing the harmful effect of crumbs being squeezed outward and deposited on the workpiece surface, while the cutting ends continue to provide distributed cutting force.
Solution Approach 2:
The recesses, which could be seen as reducing the effective cutting surface area, actually convert the harmful effect of chip accumulation into a beneficial chip management system. By providing designated spaces for chip storage within the screw head structure, the design prevents crumbs from contaminating the workpiece surface while maintaining effective cutting force distribution across multiple ends.
Data Source
AI summary
A screw includes a head and a shank extending from the head and defining a longitudinal axis. A thread is provided on the shank. The head includes a top portion and a cone portion located between the top portion and the shank. A plurality of recesses is provided in a peripheral surface of the cone portion and spaced in a circumferential direction of the cone portion. Each recess includes first and second side edges opposite to each other in the circumferential direction and an upper edge connecting the first and second side edges. The first side edge features a maximum recess depth greater than a maximum recess depth of the second side edge. The top edge extending in the circumferential direction of the cone portion is partially arranged between the top portion and the first side edge of an adjacent recess in the longitudinal axis direction.