How to Calculate Surface Roughness
What is Surface Roughness?
Surface roughness affects friction, wear, fatigue, and appearance. Proper specification prevents unnecessary cost or inadequate performance.
Step-by-Step Guide
- 1Measure Ra (average roughness) in micrometers or microinches
- 2Typical values: rough (3.2-6.3 μm), normal (0.8-1.6 μm), smooth (0.05-0.2 μm)
- 3Specify based on functional requirements
Worked Examples
Input
Bearing surface typically requires Ra <0.4 μm (smooth)
Result
Specify fine grinding or lapping
Affects bearing life
Common Mistakes to Avoid
- ✕Over-specifying finish (unnecessary cost)
- ✕Under-specifying and causing functional problems
Frequently Asked Questions
Why does roughness matter for bearings?
Rough surfaces cause higher friction and wear. Smooth surfaces reduce wear 10-100×.
Does fine surface finish improve fatigue strength?
Yes, polished surfaces have ~50% higher fatigue strength than rough surfaces.
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