Conversion of surface finish measurements

[Ron Rompen]

Anyone have a quick reference for conversion (approximate) between Ra and Rz values for ground surfaces?

Print requirement is for Rz 10, I would like to propse to the customer that Ra 1.6 max (by comparison to a recognized standard) would meet or exceed this requirement.

Anyone have any suggestions?

[Jim Wynne]

I'm not sure that a reasonable conversion is possible, given that the Ra and Rz are measurements of two different (albeit related) attributes. See this page for more information which nonetheless might help you to make your case.

[Bobh@pte]

ry this for an explanation.
http://www.mmsonline.com/articles/1102gage.html

[apestate]

I always thought it interesting that piston engine cylinders are bored and then honed, but the honing is designed to leave surface pits and imperfections and not totally smooth the surface, which allows oil from the crank case to lubricate the ultra-tight fit of the piston.

The moral of my beautiful vignette is that there are many many parameters for measures of surface roughness, all designed for different attributes of the finish as Jim said.

[Ron Rompen]

Thanks for the input guys. I realize that the two callouts are 'different', but since it is a cylindrical surface, it is difficult to accurately measure surface finish with my profilometer, and my comparison scale is (of course) in Ra.