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Surface finishes N1 ... N5 N6 N7 N8 N9 and their equivalents
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Current postings:
May 19, 2022Q. Could you please give me information: is there any Roughness Standard under N1 for Ra 0.025? If there is, kindly please share with me. Many thanks for your kind help.
Melissa Gulstudent - Turkey
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Closely related Q&A's, oldest first:
2001Q. I AM LOOKING FOR A CHART OR SOME REFERENCE RELATING N5 N6 N7 N8 N9 TO Ra VALUES.
Michael L [last name deleted for privacy by Editor]-Wyandotte, Michigan
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2001
A. Grade Numbers Older drawings may use roughness grade numbers to indicate Ra values. The following table is given in ISO 1302 [info about this spec at Amazon; and at Techstreet]
Roughness values Ra | Roughness values Ra | Roughness |
micrometers | microinches | Grade Numbers |
50 | 2000 | N12 |
25 | 1000 | N11 |
12.5 | 500 | N10 |
250 | N9 | |
3.2 | 125 | N8 |
1.6 | 63 | N7 |
0.8 | 32 | N6 |
0.4 | 16 | N5 |
0.2 | 8 | N4 |
0.1 | 4 | N3 |
0.05 | 2 | N2 |
0.025 | 1 | N1 |
Good Luck.
Bill Boatright-Raleigh, North Carolina
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2004
Hi,
I like your table. However, I believe there's a small mistake. The metric value corresponding to a 250 micro-inch surface roughness/finish should be 6.4 micrometers, rather than 8.3.
Best regards,
Justin H [last name deleted for privacy by Editor]pressure vessels - Erie, Pennsylvania
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2002
Q. Bill,
Great chart! Is this a new ISO standard for all metal surfaces?
Thanks,

Michael Liu Taylor
specialty stainless steel distributor - Dallas, Texas
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Q. One of our Customer Drawings indicate a Surface Finish specification of N6.
We only have a Surface Finish Tester that can measure Rz & Ra.
Where Can I find or how do I convert N to Rz?
Henry R [last name deleted for privacy by Editor]automotive engineering - Benoni, Gauteng, South Africa
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A. Hi, Henry. You can see that the chart tells you N6 = Ra of 32 microinches. So your test device which measures Ra should work.
If you search the site for "Ra vs Rz" you will see that while they tend to generally track each other, they measure different things and cannot "be converted".
Sort of like taller people tend, on average, to weigh more than shorter people but you cannot convert people's height to their weight. If you want to 'convert' from one to the other you need large safety factors in each direction, which is very wasteful. An average person of five foot height might weigh 100 pounds but that does mean that a 120 pound person is taller than five foot -- they might even be shorter :-)
Thus the same truism is repeated on one surface metrology site after another after another: Do not attempt to "convert" or "correlate" -- If you want to know the Ra, measure the Ra; if you want to know the Rz, measure the Rz! :-)
Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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2005
Q. I am trying to find out what a 63µ finish is? I have put this finish on a polycarbonate part that needs to be machined.
Thank you for your help.
machining - Melbourne, Florida
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April 23, 2008
A. Hi, Bruno. That is the symbol for micrometers, so it would be a '63 micron finish'. Good luck.
Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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April 23, 2008
Q. Hi
I'm a student and have a confusion that which is a better surface finish of these two:
N5 or N10 ?
UET - Taxila, Pakistan
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May 2008
A. Hi, Waqas. In the chart above, rougher finishes are at the top and smoother finishes are at the bottom.
Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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June 22, 2010
Q. Hello Sir!
My name is Emre Özcan, I'm 24 years old, metallurgical and materials engineer at a machinery shop at Turkey.I am also a MSc. Student. We have a little troubleshooting about the interpretation of a roughness value on a technical drawing that came from one of our customers.
While I was searching for answers regarding this problem, I have seen your article on the www.qualitydigest.com/june01/html/surface.html website and I have got your e-mail from this website. I decided to consult this problem to you and I'm wondering if you can help me out in this problem?
The problem is simple: We have a furnace roll on the technical drawing, and the surface roughness value of this roll is represented with "CRODAN #3" or "CRDDAN #3".This is the surface roughness value of grounded and sandblasted condition of the piece. We have no idea what CRODAN #3 is. Can you tell us the Ra equivalent of this value?
Thanks in advance,
- Ankara, Turkey
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July 5, 2010
Q. The table above is in our SABS 0111 - Engineering Drawing Standard, but how do we relate the numbers to a physical finish or machining method? I.e., what code for a standard turning finish, a good milling finish or for a ground and polished finish)
William Jackson- Durban, South Africa
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January 16, 2012
Q. MPc. I have a surface condition of 12S. What does it mean and how does it convert to 118 Ra?
Hector G.- Chicago, Illinois
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January 17, 2012
Apologies, Hector, but I'm not familiar with "MPc" in this context, nor with "12S" in this context, nor with what you even mean by "convert to 118 Ra". Sorry.
Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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February 6, 2012
Q. Can anybody tell me how the ISO surface finish is used on a drawing?
Thank you all!
- Dublin, Ohio, United States
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April 9, 2015
Q. I have a customer looking for a finish of "UOS-125AA". I can't find it.
Dennis Kimball- Auburn, Massachusetts USA
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April 2015
Hi Dennis. When we google something and don't come up with a definitive answer, it usually means the phrase doesn't have a universally accepted meaning ... so we'd better talk to the customer or a contract dispute could be brewing :-(
My guess is that it means 'Unless Otherwise Stated (all surfaces to be finished to) 125 Arithmetic Average', but if an unhappy customer faults you for not building it to 'Utterly Outrageous Standard 125 As Amended', it will be 100% your fault rather than theirs because you should not have guessed :-)
Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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Least expensive way to get N8 finish?
May 21, 2019Q. Which machine is capable of finishing N8 surface finish? Is it Band saw finish or Milling Finish or Ground Finish? Going for better finish like grinding will increase cost. Therefore want to stick with minimum requirement; please advise.
MADHUSUDAN SONTHALIAManufacturing - Jaipur, Rajasthan Country INDIA
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May 2019
A. Hi Madhusdan. What sort of components, what production volume, and what material of construction? Typically, bulk finishing (tumbling, vibratory finishing, etc.) is the least expensive way to a smooth finish because it doesn't require individual handling.
Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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May 21, 2019
Q. Hello,
We have to machine Graphite parts and the drawing specifies N8 & N6 finish.
The machining can be done on a bandsaw as well as on a milling machine. Hence we need the clarification with regard to the tolerance level in N8 & N6 finish, so we could choose the most economical method to machine the part.
- Jaipur India
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May 2019
A. Hi again. Sorry, I am not experienced with machining graphite, but I have read that it can be molded from different grain size, which affects the smoothness of cut, and also that it tends to fracture off, leaving pits if milled from the outside in. With metal, a bandsaw cut is usually rough, and the faster the cut the rougher. I can only guess that you may be able to cut graphite with a bandsaw to an N8 finish but not an N6 -- but guessing is all I can do :-) Hopefully someone experienced with machining graphite and measuring the smoothness will chime in. Good luck.
Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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June 13, 2021
Yes to Ted's answer. You can get a N9 finish for sure, with a bandsaw, N8 if you are using a good blade with fine teeth.
N6 finish will need to be machined.
- Green Bay, Wisconsin
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