surface finish in RMS
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: surface finish in RMS
: surface finish in RMS -- JohnsonSignCo	Post Reply	Top of thread	Engineering Forum

Posted by: moaweh ® 04/21/2010, 22:41:33 Author Profile eMail author Edit

RMA(RA) Stand for Root Mean Square(Roughness Average), it is a term used to measure the roughness of a surface,RMS 63 is a smooth surface finish, RMS 125 is an average manufacturing surface, RMS 25 is a very clean smooth surface finish. There are several tools to use to acomplish such surface finish.... RMS is required usally in the most demanding fluids applications. Mike A Abuhatoum. Modified by moaweh at Wed, Apr 21, 2010, 22:43:43

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Re: surface finish in RMS (Ra)
: surface finish in RMS -- JohnsonSignCo	Post Reply	Top of thread	Engineering Forum

Posted by: Cragyon ® 09/15/2004, 13:25:16 Author Profile eMail author Edit

RMS (Too Mean Square) is a commonly mistaken for Ra (Roughness Average).   Roughness average is a specification which controls the average extremes of the surface irregularities that result from the manufacturing tool used to cut the metal.  These are the mico-scores on the surface of the metal. Check out the following page /surface_finish.htm

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Re: surface finish in RMS (Ra)
: Re: surface finish in RMS (Ra) -- Cragyon	Post Reply	Top of thread	Engineering Forum

Posted by: randykimball ® 09/15/2004, 18:37:07 Author Profile eMail author Edit

True. For those not accustomed to RMS here are some familiar atricles I hope you can relate to. Although RMS (roughness measurement system) is generally used to describe metal cutting surface finish there is no reason not to use it most anywhere you wish. My cell phone has an RMS of around 32, smoother would make it too slippery. A song on a long play phono album (for those that member) is around 125. A magazine cover is about 16. A business card is between 32 and a 16.. A mirror or window is about 4. A strip of duck tape feels about 250. By the way, duck tape was named because it would work under water during WW II, .... not from being used as a duct tape as is commonly thought. The face of a plastic spoon is around 16 to 8. I haven't spotted a good example of a 500 RMS, But... generally a fairly well done torch cut is about a 500 RMS. Please realize these items are not actually the RMS I suggest, this is simply a general touch and feel test. They would test much differently. But... this gives you a reasonable and useful set of examples. As you noticed there is a tendency to use 4, 8, 16, 32, 64, 125, 250, and 500 as common numbers to call out on a product. -randy- The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Wed, Sep 15, 2004, 18:39:50

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Re: Re: surface finish in RMS (Ra)
: Re: surface finish in RMS (Ra) -- randykimball	Post Reply	Top of thread	Engineering Forum

Posted by: 993334236 ® 01/12/2007, 11:21:19 Author Profile eMail author Edit

RMS actually stands for Root-Mean-Square, a statistical measurement of the square root of the average of the squares of the measurement. The RMS value is generally 11% higher than the Ra value for the same surface roughness.

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: Re: Re: surface finish in RMS (Ra)
: Re: Re: surface finish in RMS (Ra) -- 993334236	Post Reply	Top of thread	Engineering Forum

Posted by: sowen ® 02/27/2009, 19:08:44 Author Profile eMail author Edit

How did you determine the comparison between RMS and Ra value is 11%?

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: Re: Re: surface finish in RMS (Ra)
: Re: Re: surface finish in RMS (Ra) -- 993334236	Post Reply	Top of thread	Engineering Forum

Posted by: Nu2thiS ® 05/11/2008, 18:14:54 Author Profile eMail author Edit

Is rms in µin and Ra in mµ? If so what would a 63Ra finish be in rms? Our profilometer only measures in Ra, Rc, and Rz but the specs call out a 63rms finish or better. Please help. Thanks.

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: : Re: Re: surface finish in RMS (Ra)
: : Re: Re: surface finish in RMS (Ra) -- Nu2thiS	Post Reply	Top of thread	Engineering Forum

Posted by: Kelly Bramble ® 05/11/2008, 19:59:14 Author Profile eMail author Edit

Ra is typically given in micro-inches. It means Roughness average. Allmost the same as RMS. See you Machinery's handbook. The ISO folks use CLA or Center Line Average. CLA and Ra are interpreted identical. Ra, RMA, and CLA can be given in inches or MM.

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