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Interpretation of Surface Finish Symbol - Is Smoother Acceptable?

Interpretation of Surface Finish Symbol - Is Smoother Acceptable?

I've read ASME Y14.36 and scanned ASME B46.1, but can't find any specific reference to the question I have.

When the surface finish callout is placed onto the drawing, does it imply the roughest finish possible? All of the mathematics that go into calculating the average (Ra) value aside, I'm wondering if a smoother surface is permissible per standard.

For example,
  • If the drawing calls out 3.2 (125), can the surface also be 1.6 (63) or 0.80 (32) or 0.40 (16)?
  • If I require a specific range of surface roughness, how do I call out a min and max value?


RE: Interpretation of Surface Finish Symbol - Is Smoother Acceptable?

Yes, that is the maximum that is acceptable, it can be smoother. If you need to have you finish within a range you give max/min values in the same position that you normally put your target value. There are instances when you do not want a surface any smother than X, as an example the surface finish of hydraulic cylinders can be to smooth for the seals to work effectively.

RE: Interpretation of Surface Finish Symbol - Is Smoother Acceptable?

Like djhurayt says:

If a single value is given then yes my understanding is it's a maximum.

If you want a range then you put an uppper & lower value with the symbol. was referenced by the below thread on similar topic, page 37 (pdf # 40) and there is an illustration on page 38 showing max & min.

thread1103-318284: Surface Roughness General Coverage Specification

Posting guidelines FAQ731-376: Forum Policies (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Interpretation of Surface Finish Symbol - Is Smoother Acceptable?

Thanks, Kenat.

My searches didn't pull that one up, but I only did a few variants of "surface roughness," "surface finish," and "surface texture" to look for existing solutions.
And based on your prior eng-tips thread, I went back to ASME Y14.36 and did see the notation in Figure 5. (I have the 1996 edition of the standard handy.)

Thanks again. I can't believe I missed the reference the first time. Would have saved me the 108 page read of B46.1.


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