-- The Home Page of the Finishing Industry
Serious Education & the most FUN
you can have in metal finishing smiley

No popups, spam, registration or passwords
on this site
current topics
topic 19484

Does "Z" equal either "Rz, Ra, or Rmax"?

A discussion started in 2003 but continuing through 2018


I have what may appear as a rather simple question to some. We are currently in the process of "bidding" on a job that will require us to supply a Turned, Polished, Ground, and Chrome-Plated round bar product (an automotive product for overseas producer) that requires us to hold a Surface Finish of "1.6-Z". I have searched many places / resources, but all I seem to find is a reference to the "big 3" (Ra, Rmax, and Rz). Would this spec (1.6-Z) be the same as "1.6 Rz?"

Allen Flores
- LaPorte, Indiana, USA


A. Your guess is as good as mine; however, business is not a guessing game. Don't ASS.U.ME anything (this stands for a phrase). I suggest you contact customer to clarify.

tony kenton
AF Kenton
Hatboro, Pennsylvania


A. R max: Max peak to valley height within the sampling length L.
Rt: vertical height between the highest & lowest points of the profile within the evaluation length.
Rz: It is based on 10 points within one sampling length, mean distance between 5 highest peaks & 5 lowest valleys within the sampling length, measured perpendicular to the baseline of the chart.
Ra: roughness average or CLA, Centre line average.

- Chennai, India


Correlation between Roughness Average (Ra) and Total Roughness (Rt). Is there a correlation if Rt is stated as 4 µm?

Mike Murdaugh
- Stratford, Wisconsin

November 22, 2018

Q. If Rmax is the value of maximum peak of the profile, then can you please explain the difference between Rmax and Rp.

arjun sreepathi
- bangalore, karnataka, India

November 2018

A. Hi Arjun. Speaking for myself, I hate questions about surface profile because I never remember enough of the minutia and I have to keep looking it up and re-checking it; plus, it's impossible to explain what the abbreviations mean unless the questioner has a good grounding in the topic anyway :-(

To draw a distinction between two scales like Rmax and Rp -- as you are asking us to do -- requires a good understanding of what a sample length is and what an evaluation length is; none of the surface profile scales has any real meaning without that understanding.
For example, I can tell you that Rmax is the maximum difference between a peak and a valley of any one sample length and that Rp & Rv are respectively the maximum peak height and valley depth within the evaluation length. So you might at first think this means that Rmax = Rp + Rv ... but it doesn't ... because Rp and Rv are more likely in different sample lengths than in the same sample length. Rather, as Meenashi instructs us above, Rp + Rv = Rt :-)


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

December 2, 2018

A. Ummm "Rp + Rv = Rt".

I think no. Rather: Rt = Rp-Rv.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

December 2018

A. As always, your comments are highly appreciated Jeffrey. But I'm gonna stick with yes, Rp + Rv = Rt :-)


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

If you have a question in mind which seems off topic, please Search the Site

ADD a Comment to THIS thread START a NEW threadView CURRENT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices

©1995-2018, Inc., Pine Beach, NJ   -   About   -  Privacy Policy
How Google uses data when you visit this site.