Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Surface finish conversion table
I would like to know if there is a conversion formula or chart out there to convert an Rz scale reading to an Ra reading. I have a profilometer that reads Ra and a blueprint that has Rz63 finish callout on it.
Ron Sikorski- South Bend, Indiana
2003
Rz is is the same as RMS; however, the spec covers a specific numbers of ridges and valleys of the surface profile. Ra can vary with the machining process. A rough guide line is either to divide or multiple by 4 times either or.
AF Kenton
retired business owner - Hatboro, Pennsylvania
2003
I thought it was multiply/divide by 40 per www.sinama.com.tw/page15.html
Trevor Altman- Walpole, Massachusetts, USA
May 26, 2011
May 27, 2011
A meter is 39.37 inches -- roughly speaking, 40 inches. That's
why you multiply by 40 when converting from metric to English units,
and divide by 40 when going the other direction. But that does not
tell you how to convert from Rz to Ra.
In fact, there is no "conversion" because they are
measuring different things. It's like converting a car or truck's
horsepower to torque; there is no conversion, just a guideline that
the torque is probably somewhere in the range of y to z if the
horsepower is z.
Tony's 4 to 1 is approximate but not "safe".
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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