Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Metric surface finish symbols

Q. I am trying to find out what the symbol "N9"for a finish requirement converts to in Ra.

Thanks

Paul Sawiski
machining operations - Avon, Massachusetts, USA
2004

A. Roughness grade N9 = 6.3 Ra (in micro meter, which is equivalent to 250 Ra (in micro inches)

Regards,

Niranjan S. Kulkarni
- India
2004

Q. I AM LOOKING FOR A CHART FOR ALL OF THE ROUGHNESS IN THE N GRADES. N5,N6,N7 ETC.

MEL WIGTON
- DENISON, TEXAS
2005

Q. What is the inch equivalent of metric 3.2 surface finish?
Is there a chart for metric or conversion?

Dean Edward Peters
fabricating - Lewisville, Texas
2006

A. 3.2µm (micrometer) is equivalent to 125 µin (128 µin to be exact) or Grade N8
It is customary to convert metric roughness to imperial roughness by multiplying 40 to the metric roughness
So:
3.2 µm * 40 µin/um = 128 µin

Ed Chan
- Waterloo, On, Canada
2006

Q. Could you tell me what N7 in surface finish is in inch.

Jack Banks
- Cotopaxi, Colorado USA
August 12, 2008

A. Hi. The chart that Mel and Jack are looking for is on letter 7560.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 14, 2008

Q. What metric standard defines the "N" series surface roughness. Has the standard 1.6 roughness callout been phased out to read N7?

Paul Cunningham
- Fremont, California
January 4, 2013

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