Linear Guide & Ball Screw Life Calculator
Rating life of ball and roller linear guides (km) and ball screws (revolutions) from the dynamic load rating and applied load, with load factors and conversion to hours from stroke and speed
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Calculates the L₁₀ rating life of a ball or roller linear guide and of a ball screw from the catalogue load rating and the applied load, with load, hardness, temperature and contact factors, and converts it into hours and years.
How to use
- Choose the "Type" and, for a ball guide, the "Rating distance of C in the catalogue".
- Enter the "Basic dynamic load rating C" and the "Applied load" as one value, radial + lateral, or up to four load steps.
- Pick the "Operating conditions (load factor fw)" and adjust fH, fT and fC if the catalogue asks for them.
- Under "Operating pattern", enter the "Stroke length" and "Cycles per minute (out and back)" or an average speed, and the "Operating hours per day".
- Read the rating life in km (or million revolutions), the hours and the years.
How it works
- Ball guide: L = (fH × fT × fC ÷ fw × C ÷ P)³ × 50 km; roller guide: exponent 10/3 and 100 km; ball screw: (C ÷ (fw × F))³ × 10⁶ revolutions.
- Hours = L × 10⁶ ÷ (2 × stroke × cycles per minute × 60). A varying load is averaged as the cubic mean of the steps.
- L₁₀ is the distance 90 % of identical units reach without fatigue flaking. Moment loads, preload, mounting and lubrication are not modelled.
Questions and answers
- How do I calculate the life of an LM guide?
- Divide the load rating by the applied load, cube it and multiply by 50 km. C = 10 kN, P = 2 kN and fw = 1.2 give about 3,600 km.
- What is the load factor fw?
- A factor for vibration and impact: 1.0 to 1.2 for smooth motion, 1.2 to 1.5 for normal, 1.5 to 2.0 with impact or over 60 m/min.
- How do I convert km of life into hours?
- Distance per minute = 2 × stroke × cycles per minute; divide the life by it. 3,600 km at 500 mm and 10 cycles per minute is about 6,000 hours.
- Why is C rated for 50 km in one catalogue and 100 km in another?
- The rating is defined for a reference distance, so the same part gets different C values. Use the distance of the catalogue the C came from.