Surface Roughness - Conversion of RS on a Print to RZ

qcman

Registered Visitor
Hope this is the correct place for this. I have a Honda surface roughness spec of RS 6 um max called out on a print per JIS B 0651 for a functional extrusion part. Does anyone know of a conversion chart or know the conversion of RS to RZ?
 

JeantheBigone

Quite Involved in Discussions
First off, here is a conversion chart that I've found useful.

https://www.csbslidingbearings.com/uploads/1/5/6/9/15694310/surface_roughness.pdf

Second, RS is not a common parameter for describing surface roughness. I've seen it equated to "RMS" https://www.engineersedge.com/surface_finish.htm
but also to the mean spacing between peaks.
https://www.hse.gov.uk/research/rrpdf/rr549.pdf
Then there is an indication that Rs may be the same as Ra from early days of measurement. I've posted an image from George VanderVoort's book "Applied Metallography."

I wish I could give you a definitive answer. Is there any more information you might be able to provide? Age of the drawing? A shot of the callout?
 

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qcman

Registered Visitor
All customers requiring surface roughness measurements ask for it in RZ except this one. I did find one conversion chart but the conversion number from RS to RZ didn't seem right. Our normal RZ readings on similar extrusions is between 1.45 - 2.90. I have attached the chart I found as well as the spec call out / procedure last updated in 1989. Thank you for the links and time.
 

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