We are doing a custom Stainless Steel part where we need the surface finish on the end of a fitting needs to be Ra < 10 microinches because it's a metal to metal seal for gas media.

We have a surface tester but the seal is a small lobe or bump on the fitting end that is too small for our surface tester to ride on:

http://elsmar.com/jpg/faceseal.jpg
image grabbed of the internet and I put inthe text.
(very similar to a Swagelok "VCR" seal if you're familiar with these fittings)

We will be roller burnishing the lobe and bore AND sending the part for electro polishing.

I'm proposing the following:
1) Acquire a traceable visual standard for 10 Ra microInches
2) Sample the parts after electro polishing and test an appropriate number on the surface tester on the inner bore. If this is 10 or less AND, under magnification, the lobe looks comperable to the standard with no defects it's good.

It's a tough standard, but it's not for enough parts to justify more than a traceable visual standard, equipmentwise.

Thoughts?

I believe it can be evaluated with a laser surface finish tester.

For example:
Cobra Laser Profile Scanner
(http://www.inspectionengineering.com/OGP_Cobra.htm)

You could send parts out hand have them evaluated to the requirement with a laser, and use them as the standard. Might be better than a standard that might have a different lay. You should have pass and fail, or people will quibble over the near misses.
:cool:

If you need to use finishing standards then go to:
stainless International.com or www.ssina.com

You can get certified standards