Machine Spindle Bearing Life Calculator

L10 is the life that 90% of identical bearings reach under the same load and speed before the first sign of fatigue — equivalently, a 10% failure probability. Median life is roughly 5× L10. It is a statistical fatigue life, not a guarantee for any single bearing.

Yes — preload is a real, permanent axial force the balls carry on every revolution, and it must be folded into the equivalent load P. That is the trade of rigidity vs life: heavier preload stiffens the spindle for finishing accuracy but raises P around the clock. Use the bearing maker's preload-class tables to get the equivalent P contribution rather than guessing.

C (basic dynamic load rating) is printed in every bearing datasheet — for example a 7014 angular-contact pair (C ≈ 49 kN per row) in a milling spindle at 8,000 rpm. P is the equivalent dynamic load: for pure radial load it is simply the radial force; with combined radial + axial load use P = X·Fr + Y·Fa with X and Y from the datasheet.

Because L10 assumes clean lubricant, correct fit and alignment. In practice most bearings die of lubrication failure, contamination, misalignment or fitting damage rather than fatigue. If yours fail early, check the actual load path and the grease before blaming the bearing.

Use p = 3 for ball bearings and p = 10/3 for roller bearings (cylindrical, spherical, taper). Rollers carry load on a line contact rather than a point, so their life is less sensitive to load — that is what the higher exponent encodes.