# Surface finish conversions from English to metric

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Q. I would like to convert surface finish from English to metric numbers, i.e.:

What is a metric equivalent to a 32 µinch surface finish.

Thanks Andy

Andy Whitetelecommunications - Amesbury , Massachusetts

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A. The conversion factor between micro-inches (µ") and micro-meters (µm) is multiplying by 0.025 which is equivalent to dividing by 40. In the conversion requested, 32 micro-inches are therefore equal to 0.8 micro-meters.

Best regards,

Giovanni M. Cirianimetallic watch bands - Altavilla, VI, Italy

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A. 1 meter = 39.37 inch.

.000032 inch divided by 39.37 equals .000000812 meter

32 micro-inch equals .8 micro-meter.

- Fullerton, California

+++++ March 17, 2009

Q. So what is the correct conversion for a Rz25 finish?

Dan Whitemachine shop - Appleton Wisconsin

A. Hi, Dan. Proceeding exactly per Giovanni and Oscar again --

1 meter = 39.37 inch.

.000025 inch divided by 39.37 equals .000000625 meter;

25 micro-inch Rz equals .6 micro-meter Rz.

Regards,

Ted Mooney, P.E. RET finishing.com Pine Beach, New Jersey |

July 23, 2012

Q. What is the US finish call-out for European Ra 63 finish?

Anthony Mastropolo- Pleasant Prairie, Wisconsin USA

Hi Anthony.

The US equivalent of an Ra 63µm finish would, as explained above, be Ra 2520 µin., which sounds too rough a finish to be a reasonable answer. It sounds to me like maybe you may already have the US callout; but if you can present the details of your situation, I think we can probably help. Good luck.

Regards,

Ted Mooney, P.E. RET finishing.com Pine Beach, New Jersey |

## MICRO FINISH CONVERSION FROM Rz TO MICRO INCHES

February 20, 2008Q. I HAVE A PRINT WHERE ALL DIMENSIONS ARE IN MILLIMETERS (METRIC). IT HAS A SURFACE ROUGHNESS ON IT LISTED AS Rz 16 WHICH I AM UNFAMILIAR WITH. TO UNDERSTAND IT I AM TRYING TO DO A CONVERSION TO MICRO INCHES WHICH I AM FAMILIAR WITH. THIS IS INTERESTING TO ME AS MY COMPANY IS SEEING MORE EUROPEAN PRINTS OF PARTS TO QUOTE. SOME FORMULA TO CONVERT THIS WOULD BE HELPFUL FOR MYSELF AND OTHERS AS WELL. I AM IN THE METAL STAMPING INDUSTRY WHERE MOST OF OUR PRODUCTS ARE SPECIAL WASHERS FOR AUTOMOTIVE APPLICATIONS.

JEFF RINK- WARREN, Michigan USA

March 18, 2015

A. Well, I am familiar with that situation since we are working for overseas companies and their way to work in mm.

This is what we are doing to convert from mm to micro inches: we multiply mm X 0.03937

Example .04 X 0.03937 = 0.0015748 with is equal to 16.

Hope you can do it.

- Chicago Illinois usa

March 2015

Hi Leo. Thanks. I think your conversion factor is correct for converting mm to inches, but not micro inches. Rz 16 µm would be Rz 630 µ-inch.

Jeff would need to be cautious what "Rz 16" actually means though. As Alex Tabenkin says in his article "To Each His Own Parameter" (www.qualitydigest.com/june01/html/surface.html): *"If your print calls out an Rz value with no further explanation, warning bells should go off. A time bomb may be ticking."*

Regards,

Ted Mooney, P.E. RET finishing.com Pine Beach, New Jersey |