Spindle Assembly Collet Seat Angle and Coating
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Solution Overview
Problem
Davenport multi-spindle screw machines struggle to effectively machine bar-stock made of harder materials due to insufficient strength and rigidity in spindle assemblies, particularly when handling larger diameters like one-inch round bar-stock, leading to issues with holding the workpiece against rotational and axial movement during machining operations.
Innovation Solution
The improved spindle assembly features a collet seat angle greater than 7° and less than or equal to 25°, with low-friction coatings on the cam surfaces, and a radially thickened spindle design to enhance rigidity and stiffness, allowing for better grip on bar-stock materials, including those with low machinability ratings, and accommodating up to one-inch round and polygonal bar-stock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the spindle assembly uses a standard collet seat angle (29.5°) and regular capacity design, then it can machine softer materials (5/8-inch diameter), but it cannot adequately hold harder materials (one-inch diameter) against rotational and axial movement during machining
Solution Approach 1:
The patent changes the collet seat angle parameter from the standard 29.5° to a reduced angle between 7° and 25°. This parameter change increases the axial holding force component while maintaining radial clamping force, enabling the spindle to securely hold harder materials (such as Inconel, Hastelloy, Waspalloy) and larger diameter bar-stock (up to one-inch) against machining forces without excessive radial displacement
Solution Approach 2:
The patent employs low-friction coatings (such as PTFE, MoS2, or diamond-like carbon) on the cam surfaces to dynamically reduce friction during collet actuation. This allows the collet fingers to move more freely along the cam surfaces, improving the responsiveness and accuracy of the clamping action, which is critical for maintaining consistent holding force on hard materials that generate higher machining forces
2Adaptability or versatility
If the spindle assembly is designed for larger diameter bar-stock (one-inch round), then it can accommodate bigger workpieces, but the radial thickness of spindle components must be reduced, decreasing strength and rigidity
Solution Approach 1:
The patent changes the collet seat angle parameter from the standard 29.5° to a reduced angle between 7° and 25°. This parameter change increases the axial holding force component while maintaining radial clamping force, enabling the spindle to securely hold harder materials (such as Inconel, Hastelloy, Waspalloy) and larger diameter bar-stock (up to one-inch) against machining forces without excessive radial displacement
Solution Approach 2:
The patent employs low-friction coatings (such as PTFE, MoS2, or diamond-like carbon) on the cam surfaces to dynamically reduce friction during collet actuation. This allows the collet fingers to move more freely along the cam surfaces, improving the responsiveness and accuracy of the clamping action, which is critical for maintaining consistent holding force on hard materials that generate higher machining forces
3Strength
If the collet fingers are moved radially inwardly to grip the bar-stock, then holding force increases, but friction against the cam surfaces increases, reducing operational smoothness and increasing wear
Solution Approach 1:
The patent replaces the traditional high-friction mechanical interface between collet fingers and cam surfaces with a low-friction coating system. Coatings such as PTFE (polytetrafluoroethylene), MoS2 (molybdenum disulfide), or diamond-like carbon are applied to the cam surfaces, reducing the coefficient of friction and enabling smooth collet actuation even under high gripping forces required for hard materials
Solution Approach 2:
The patent changes the collet seat angle parameter from the standard 29.5° to a reduced angle between 7° and 25°. This parameter change increases the axial holding force component while maintaining radial clamping force, enabling the spindle to securely hold harder materials (such as Inconel, Hastelloy, Waspalloy) and larger diameter bar-stock (up to one-inch) against machining forces without excessive radial displacement
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 enhanced spindle assembly effectively holds bar-stock against rotational and axial movement during machining, improving machining tolerances and reducing tool wear, enabling the use of previously difficult-to-machine materials with increased machining efficiency.
Implementation Method 1
low-friction coatings on the cam surfaces
Data Source
AI summary
An improved spindle assembly for a Davenport® multi-axis screw machine is adapted to adequately hold one-inch round bar-stock in a collet against movement relative thereto attributable to machining operations performed on a cantilevered length of bar-stock held in and extending beyond the collet. The spindle assembly may permit the use of the screw machine on materials thought heretofore to be too difficult to machine on a screw machine. Cam surfaces on the inner spindle and collet may be coated with a low-friction material. A stress-relieving connection between the inner spindle and collet is provided.