Cutting Tool Joint with T-Shaped Shaft and Inlay
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Solution Overview
Problem
Existing cutting tool joints, such as those in scissors, face challenges with sharp corners on metal shafts and holes leading to difficult assembly, material wear, and a loose joint that affects performance due to scratches and changed tension over time.
Innovation Solution
The use of inlays in the blades' holes and a T-shaped shaft with transverse shoulders that engage with an inclined surface to facilitate easy assembly and disassembly, allowing for optimal shaping and material selection, and manufacturing via injection-molding for precise tolerances and rounded edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal shaft with sharp corners and a metal hole with sharp corners are used, then the joint can be permanently attached, but it becomes difficult to assemble and disassemble, and causes material wear leading to loose joint
Solution Approach 1:
The patent applies curvature by replacing sharp corners with rounded edges on the shaft and hole surfaces. The shaft has rounded edges instead of sharp corners, and the hole has a rounded shape that accommodates the shaft. This curvature eliminates the harmful sharp edges that cause scratches and wear, while maintaining easy assembly and disassembly throughout the product lifetime.
Solution Approach 2:
The joint is segmented into distinct components: a shaft with transverse shoulders, a hole with rounded shape, and an engagement mechanism. This segmentation allows independent optimization of each component - the shaft can be designed for easy insertion while the hole provides the locking mechanism, resolving the contradiction between permanent attachment and ease of assembly.
2Reliability
If a rivet is used to permanently attach the first and second lever, then the joint remains tight, but it becomes difficult to detach the parts and adjust tension
Solution Approach 1:
The joint transitions from a static permanent attachment (rivet) to a dynamic reversible connection. The shaft can be inserted and removed from the hole by rotating the lever, allowing the joint to maintain tightness during use while enabling easy detachment and tension adjustment when needed. This dynamic characteristic resolves the contradiction between permanent attachment and ease of repair.
Solution Approach 2:
Instead of using a rivet that protrudes through both levers to create permanent attachment, the patent inverts the approach by using a shaft that fits into a hole, where the shaft's transverse shoulders engage with the hole's rounded shape. This inversion allows the male-female connection to be easily assembled and disassembled while maintaining joint tightness, eliminating the need for permanent rivet attachment.
3Ease of manufacture
If sharp edges on the shaft and hole are used, then manufacturing is simpler, but scratches appear during use causing material wear and joint loosening
Solution Approach 1:
The patent applies curvature by replacing sharp corners with rounded edges on the shaft and hole surfaces. The shaft has rounded edges instead of sharp corners, and the hole has a rounded shape that accommodates the shaft. This curvature eliminates the harmful sharp edges that cause scratches and wear, while maintaining easy assembly and disassembly throughout the product lifetime.
Solution Approach 2:
The rounded edges and surfaces act as a cushioning mechanism that prevents direct contact between sharp edges during assembly and use. This beforehand cushioning protects the material from scratches and wear that would otherwise occur with sharp corners, ensuring joint durability throughout the product lifetime.
Data Source
Figure 1~3
Figure 4~5
AI summary
The invention relates to a cutting tool (1) comprising a first (2) and second (3) blade attached to each other by a joint (4), and a first (5) and second (6) handle. In order to obtain efficiently an optimal shape for the joint, the cutting tool comprises a first inlay (8) having a protruding end (9) protruding into a hole (10) in the first blade (2), a shaft (13) with a first end (14) joined to the protruding end (9) of the first inlay (8) and with a second end (15) having at least one transverse shoulder (16), a second inlay (17) having a protruding end (18) protruding into a hole (19) in the second blade (3) and a hole (22) receiving the second end (15) of the shaft (13), and an engaging surface (23) for engaging with the shoulder (16) of the shaft (13). The the hole (22) of the second inlay (17) has a shape and width allowing the second end (15) of the shaft (13) with the shoulder (16) pass into the hole (22) in a release position, but prevents the shaft (13) and shoulder (16) from passing through the hole (22) when the shaft (13) and second inlay (17) are not in the release position.