Angled Finger Joint Geometry for Wood Strength
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Solution Overview
Problem
Conventional finger joints in wood and wood-based materials lack sufficient strength, particularly in applications where increased durability is needed for longer units or structures.
Innovation Solution
A method of forming a finger joint with projections and notches where the plane of the projection tips or notch bottoms extends at an angle other than a right angle to the longitudinal direction, increasing the effective contact surface and enhancing joint strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional finger joints with right-angled projections and notches are used, then the joint structure is simple and easy to manufacture, but the joint strength is insufficient
Solution Approach 1:
The patent applies asymmetry by changing the joint angle from the conventional right angle (90 degrees) to an oblique angle (45-60 degrees). This asymmetric modification of the projection and notch geometry increases the contact surface area between mating parts, thereby enhancing joint strength while maintaining manufacturing simplicity through standard woodworking tools
Solution Approach 2:
The patent introduces a dimensional change by extending the joint geometry from a simple right-angled configuration to an oblique configuration. This dimensional modification creates additional contact area along the length of the projections and notches, transforming the joint from a point-contact to a line-contact system, which significantly improves load distribution and joint strength
2Strength
If the contact surface between projections and notches is increased by changing the angle, then the joint strength improves, but the manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the joint angle parameter from 90 degrees to 45-60 degrees. This parameter optimization increases the contact surface area and improves joint strength while remaining within the capabilities of standard woodworking equipment, thus balancing manufacturing ease with performance enhancement
Data Source
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AI summary
This document discloses a joint system comprising first and second members (1, 2) formed of wood or wood based material. The members are joined in an end-to-end relationship along a longitudinal direction (L) by means of a finger joint (3). An end portion of the first member (1) presents a plurality of parallel straight finger-like projections (31), which enter and engage a plurality of complementary parallel straight notches (32) provided between projections (31) on the second member. A plane (Pt) comprising substantially the entire length of each projection tip (312), and/or a plane (Pn) comprising substantially the entire length of each notch bottom (321), extends at an angle (a) other than a right angle to the longitudinal direction (L).