Replaceable Cutting Head Thread Root Geometry for Stress Fracture Resistance
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Solution Overview
Problem
Rotary cutting tools with traditional external threads are prone to stress fracture at the small radius where the external roots merge with the loaded surface, leading to reduced tool life and potential failure.
Innovation Solution
A replaceable cutting head with a straight external thread design featuring concavely curved roots and a specific radial distance configuration that reduces stress concentration, allowing for improved distribution of stress and secure threaded coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If external threads have straight roots with small radius where they merge with the external loaded surface, then the manufacturing is simpler, but the threads are prone to stress fracture at the merge region
Solution Approach 1:
The patent applies curvature by transitioning from straight external roots to concavely curved external roots. The curved root profile with optimized radius distributes stress more evenly along the root-loaded surface transition zone, eliminating the stress concentration that occurs at the sharp corner of straight roots. This curvature modification directly addresses the stress fracture issue while maintaining manufacturability through standard threading processes.
Solution Approach 2:
The patent modifies the geometric parameters of the external thread root by specifying a concave curvature radius that is at least 0.05 inches and less than one-sixth of the external thread pitch. This parameter change transforms the root geometry from a sharp transition to a gradual curve, reducing stress concentration factors and improving fatigue resistance without significantly complicating the manufacturing process.
2Reliability
If external roots are made with larger radius to reduce stress concentration, then stress distribution improves, but the thread geometry becomes more complex
Solution Approach 1:
The patent optimizes the root radius parameter within specific bounds (at least 0.05 inches and less than one-sixth of the external thread pitch). This controlled parameter change achieves sufficient stress distribution improvement without excessive radius that would complicate manufacturing. The specified range balances stress reduction benefits against geometric complexity and manufacturability constraints.
Data Source
AI summary
A rotary cutting tool includes a replaceable cutting head and a tool holder. The replaceable cutting head includes a forward cutting portion and a rearward mounting portion. The mounting portion includes a male coupling member that includes an external thread defined by external inner and outer cylinders. The external thread has concavely curved external thread roots which each merge with a respective straight external loaded surface at a first external root point. The first external root point is spaced apart from the external inner cylinder by a first external radial distance. The first external radial distance is greater than a third and less than two thirds of the external thread height. The tool holder includes a female coupling member that includes an internal thread. When the rotary cutting tool is in a locked position, the external thread is threadingly engaged with the internal thread.