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Ra - roughness clarification

Can someone explain exactly what is being measured in an Ra surface roughness spec. Is it an average of the peak to valley heights over the measured surface?

John Cianciolo
- Salem, New Hampshire, USA
2001

The Ra is an average of the peaks an valleys of a surface finish. The difference in the highest peak and lowest valley is commonly referred to as the Rmax.

Daryl Spindler, CEF
decorative nickel-chrome plating - Greenbrier, Tennessee
2001

John-

To add to Daryl's answer, I'd refer you to www.predev.com/smg/parameters.htm where there is a nice explanation of all those pesky lookalike surface roughness parameters.

Good luck!

Lee Gearhart
metallurgist - E. Aurora, New York
2001

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