Needle Bearing Tool Arm for Multi-Spindle Screw Machine
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Solution Overview
Problem
Existing Davenport multiple-spindle automatic screw machines experience increased tool chatter, decreased tool life, looser part tolerances, and shorter service intervals due to wear-induced diametrical clearance between the tool arm and revolving head cap, which limits their performance in demanding machining applications.
Innovation Solution
A radially tighter, freely rotatable connection between the tool arm and revolving head cap is achieved using needle bearings that are axially press-fit, with a hardened shaft portion to maintain a precise fit and reduce wear, replacing the traditional bronze bushing arrangement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a bronze bushing is used between the tool arm and head cap, then the connection is freely rotatable, but diametrical clearance increases due to wear causing tool chatter and loose tolerances
Solution Approach 1:
The patent changes the physical parameters of the bearing system by replacing the bronze bushing with a needle bearing assembly. This includes using hardened shaft portions (changing material hardness parameter) and pre-compressing the needle bearing (changing pre-load parameter) to eliminate diametrical clearance while maintaining rotational freedom, thereby resolving the contradiction between ease of rotation and manufacturing precision
Solution Approach 2:
The invention uses composite material construction by combining hardened steel shaft portions with needle bearings. The hardened steel provides wear resistance and dimensional stability, while the needle bearing provides low-friction rotation. This composite approach maintains free rotation while preventing clearance increase that would degrade part tolerances
2Device complexity
If a bronze bushing is used between the tool arm and head cap, then the structure is simple, but service intervals are short due to wear
Solution Approach 1:
The patent changes the material parameter of the shaft from soft low-carbon steel to hardened high-carbon steel, and changes the bearing type from bronze bushing to needle bearing. These parameter changes dramatically increase wear resistance and extend service intervals from about one week to substantially longer periods, while the modular needle bearing design keeps the overall structure relatively simple
Solution Approach 2:
The invention replaces the bronze bushing mechanical system with a needle bearing system. The needle bearing's cylindrical rollers provide superior load-bearing capacity and wear resistance compared to the bronze bushing, extending service intervals while maintaining rotational functionality. The hardened shaft portions further enhance durability without significantly increasing structural complexity
3Ease of manufacture
If low-carbon low-alloy steel shaft is used, then the cost is low, but wear causes increased diametrical clearance quickly
Solution Approach 1:
The patent applies local quality by hardening only the specific portions of the shaft that contact the needle bearing, rather than hardening the entire shaft. This localized hardening provides the necessary wear resistance and dimensional stability at the critical interface while keeping the rest of the shaft economical to manufacture. The frusto-conical recesses are also locally formed to accommodate the needle bearing, providing precise fit without requiring expensive machining throughout the entire shaft
Solution Approach 2:
The invention creates a composite material system by combining hardened steel shaft portions with needle bearings. The hardened shaft portions provide exceptional wear resistance and maintain diametrical clearance stability, while the needle bearing provides smooth rotation. This composite approach achieves high reliability comparable to or exceeding solid hardened steel, while the modular nature may reduce overall manufacturing cost compared to machining a completely solid hardened shaft
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
This solution significantly reduces tool chatter, increases tool life, tightens part tolerances, allows more aggressive speeds and feeds, and extends service intervals by up to fifty times compared to prior art, enhancing the machine's performance in demanding applications.
Implementation Method 1
the bearing is radially loaded as the bearing is installed such that the individual needles of same are elastically deformed immediately after the bearing has been installed
Implementation Method 2
A shaft (sometimes referred to as a 'tool arm stud') has been positioned between a portion of the tool arm and a portion of the revolving head cap. The shaft was typically formed of a low-carbon low-alloy steel... normal wear would cause this diametrical clearance to increase
Data Source
AI summary
An improved Davenport® multi-spindle automatic screw machine has a tool arm (14) mounted on a shaft (41) for rotational movement relative to a revolving head cap (13). A needle bearing (42, 42) is operatively arranged between the shaft and the revolving head cap. The bearing is radially loaded as said bearing is installed and that the individual needles of same remain elastically deformed by the radial load immediately after said bearing has been installed. The shaft has a hardened surface (52) that is engaged by the needles. The diameter of the shaft hardened surface portion is greater than the diameters of the adjacent shaft portions. Annular recesses (51, 53) extend into the shaft at either end of the hardened portion. These recesses have frusto-conical surfaces (55) that act as ramps to guide insertion of the press-fittable needle bearing into the space between the shaft and the head cap.