SKF
Principles of Bearing Selection and Application (Super-Precision)
Selecting super-precision bearings requires a more demanding methodology than standard bearings, focusing on high running accuracy, system stiffness, thermal stability, and maximum speed. SKF’s principles guide engineers through defining the required machining accuracy (runout, axial float), calculating cutting or dynamic loads, choosing the bearing type and arrangement (e.g., tandem+back-to-back), and determining the optimal preload — often the single most critical decision. Lubrication must be carefully selected for high-speed operation (typically oil-air or grease with very low channelling). Shaft and housing fits must be tighter than standard, and materials must have similar thermal expansion coefficients. Precision lock nuts and proper mounting are vital to preserve accuracy. SKF provides advanced calculation tools like SimPro Spindle to model complete bearing systems, enabling designers to push performance limits while ensuring reliability.
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System-Level Analysis
Considers spindle design, preload, and thermal effects as one.
Preload Optimisation
Spring or rigid preload settings for optimal stiffness vs. heat balance.
Thermal Growth Compensation
Arrangements that maintain preload as temperatures rise.
Speed Factor Maximisation
Ceramic balls and special cages achieve very high n·dm values.
Mounting Precision
Guidance on fits, lock nut torque, and runout minimisation.
Simulation-Driven Design
SKF SimPro Spindle models dynamic behaviour before prototyping.
How Preload Choice Impacts Spindle Performance
Light preload permits higher speed but reduces rigidity; heavy preload increases stiffness but generates more heat. SKF helps find the ideal preload using calculation of contact angle shift and thermal expansion. The goal is a spindle that maintains accuracy across the full speed range without excessive temperature rise.
Super-Precision Bearing Arrangements for High-Speed Milling
A typical motorised milling spindle uses a front set of hybrid ceramic angular contact bearings in tandem/back-to-back (high axial and radial stiffness) and a rear set of cylindrical roller bearings (radial support with axial freedom). SKF’s principles cover the exact force, speed, and thermal analysis for this arrangement.