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Q&As since 1989


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CLARIFICATION ON Ra Rq(RMS)

2004

SIR,

I HAVE BROWSED THE WEB, THE MACHINIST HANDBOOK, AND OTHER SOURCES BUT AM STILL NOT SATISFIED WITH THE ANSWERS I HAVE THUS FAR COME UP WITH. MY QUESTION IS CAN YOU EXPLAIN TO ME THE DIFFERENCE IN Ra AND Rq I KNOW THEY ARE NOT DIRECTLY CORRELATED BUT ONE IS AN ARITHMETIC MEAN DEVIATION (Ra) AND THE OTHER IS THE ROOT-MEAN-SQUARE OR THE RMS BUT BOTH ARE ARITHMETIC FORMULAS..... AND WHICH IS MORE WIDELY REFERENCED ON BLUEPRINTS? IS THERE A INDUSTRY STANDARD TO READ THE PRINT TO IF IT DOES NOT SPECIFY Ra OR Rq? I HAVE SEEN MANY THAT SAY RMS.

THANKS,

R.L. ROWLAND
MANUFACTURING - TULSA, Oklahoma

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This does not answer all of your questions, but I suggest you use the RMS system. I think it is and is becoming more popular than RA. Then again, as more and more European specs and certifications are being used, Rq will probably supersede RMS. Actually RMS and Rq are the same except the limit requirements are more specific.

AF Kenton
retired business owner - Hatboro, Pennsylvania
2004