Collet Jaw Stress Reduction via Mid-Span Support
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Solution Overview
Problem
Tapered collet rotary tool holders experience undesirable deformation and high stress levels at high rotational speeds due to centrifugal effects, leading to potential damage or failure of the collet jaws.
Innovation Solution
Incorporating a supporting portion in the collet receiving portion, which provides contact with the mid-portion of the collet arms, preventing excessive deformation by maintaining contact throughout the operational speed range, thereby controlling stress levels within the collet jaws.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tapered collet is used to receive and grip tool shanks, then effective tool holding is achieved, but at high rotational speeds centrifugal effects cause deformation of the collet arms and high stress levels in the jaws
Solution Approach 1:
The patent applies local quality by providing a supporting portion at a specific location within the collet receiving portion that contacts only the mid-portion of the collet arms. This localized support structure is positioned to provide reinforcement exactly where needed - at the mid-span of the arms where bending moments are highest during rotation - without interfering with the gripping function at the jaws or the overall collet operation.
Solution Approach 2:
The patent employs a composite structural approach by combining the collet arms (which need to be flexible for gripping) with a rigid supporting portion. This creates a composite system where the flexible collet arms can still deform for tool engagement while the rigid support prevents excessive deformation at high speeds, effectively combining two opposing mechanical properties in a single functional assembly.
2Ease of operation
If the collet arms are made flexible to enable gripping, then tool engagement capability is improved, but deformation control at high speeds deteriorates
Solution Approach 1:
The patent segments the collet arm structure into distinct functional zones: a flexible gripping portion at the jaws that maintains tool engagement capability, and a supported mid-portion that resists deformation. The supporting portion creates a clear separation between these zones, allowing each segment to perform its specific function optimally without compromising the other.
Solution Approach 2:
The supporting portion acts as an intermediary element between the collet body and the free-end jaws. It provides intermediate support that mediates between the need for flexibility at the gripping end and the need for stability during rotation, preventing excessive deformation while maintaining the ability to engage tools effectively.
3Productivity
If high rotational speeds are used to increase productivity, then manufacturing output is improved, but centrifugal deformation of the collet increases
Solution Approach 1:
The supporting portion provides preliminary anti-action by preemptively counteracting the centrifugal forces that cause deformation during high-speed rotation. By positioning the support before deformation can occur, the structure prevents the harmful geometric changes rather than correcting them after the fact, enabling sustained high-speed operation without shape degradation.
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 solution effectively reduces stress and deformation in the collet jaws, ensuring reliable operation at high speeds by providing structural support to the collet arms, thus preventing damage and failure.
Implementation Method 1
When used at high rotational speeds undesirable effects can begin to occur which typically give rise to high stress levels in the flexible jaws of the toolholder. The applicants have realised that one cause of such undesirable effects is an undesired deformation of the collet, in particular deformation of the arm portions of the collet which terminate in the jaws.
Data Source
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AI summary
A rotary tool holder assembly (1) comprising a collet (4) having a main body (41) and a plurality of arms (42), each of which arms (42) is arranged to flex relative to the main body (41), and each of which arms (42) comprises a first external portion (45) extending away from a point of flexure and a second external portion (43) which is tapered and extends away from the first external portion (45), each of which arms also comprises a respective jaw (43), wherein the plurality of jaws (43) of the collet (4) are arranged for holding a tool; and a collet receiving portion (3) having a bore (31) in which the collet is disposed, wherein the collet receiving portion comprises a tapered portion (31)a which is arranged to receive the second external portions (43) of the arms (42) so that interaction of the tapers during axial movement of the collet (4) relative to the receiving portion 3 in one direction will drive the jaws (43) towards the axis of the collet for gripping a carried tool, and wherein the collet receiving portion comprises a supporting portion (33), situated away from the tapered portion (31a), which is arranged to come into contact with and support the first external portion (45) of each arm when the rotary tool holder assembly is in use.