Oh, I understand the roundness should be within size tolerance.
I want to know how does the roundness "calculated" or obtained.
In addition, is that mean the diameter is the average result and the actual size become 10.003 +/-.0055?
Roundness is calculated using one of four algorithms: minimum radial separation, maximum inscribed circle, minimum circumscribed circle, or least-squares circle. Each may yield a different result!
Are you using ISO or ASME? That could make a difference about which one is the default algorithm.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
For the roundness check: ASME Y14.5 rules say that "minimum radial separation" is the default algorithm. For more specific details, check out the standard ANSI B89.3.1.
I don't know what the intent is on that report of diameter. If that's the only number given then I'd question it. Maybe they mean that 10.003 is the maximum diameter -- trying to show that it's still within spec. But it's worth asking the people who provided that report, since it's not in a standard format that I know of.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
We don't know. It should have been recorded as a maximum/minimum. But knowing that the roundness error is .011, I think there is a problem with that part. (Roundness values are to be within the size tolerance, unless the print specifically says AVG (average) next to the size designation.)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
I am trying to remember my college metrology here. There are shapes that measure out to accurate diameters, that are way out of round. Try sketching out a three-lobed shape.
Is it possible your diameter was measured at one point, only?
The diameter was measured 12 points, uniformly distributed, using CMM.
I hope I interpreted correct: It seems for me that the diameter 10.003 is an average value. Roundness represents this result's bilateral tolerance.
I think I badly worded this subject...