Formulate Diameter and Roundness
Formulate Diameter and Roundness
(OP)
For example:
The drawing callout of the part has a diameter of 10.000 +/-.005"
Using CMM to measure this part:
Diameter 10.003"
Roundness is .011".
Does anybody know how these number formulate?
The drawing callout of the part has a diameter of 10.000 +/-.005"
Using CMM to measure this part:
Diameter 10.003"
Roundness is .011".
Does anybody know how these number formulate?





RE: Formulate Diameter and Roundness
Is that "formulaic" enough?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Formulate Diameter and Roundness
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?
RE: Formulate Diameter and Roundness
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
RE: Formulate Diameter and Roundness
But is my interpretation correct?
-->that mean the diameter is the average result and the actual size become 10.003 +/-.0055?
RE: Formulate Diameter and Roundness
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
RE: Formulate Diameter and Roundness
Given that "roundness" is ISO term and ASME now has "circularity"
And who knows which standard the CMM follows? Sometimes it's own...
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Formulate Diameter and Roundness
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Formulate Diameter and Roundness
The size could be some sort of average, like least squares size. Then "roundness" tells us how far the part extends from that average.
I guess the only way is to ask CMM people exactly "how these numbers formulate?"
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Formulate Diameter and Roundness
So the number of the diameter is average?
RE: Formulate Diameter and Roundness
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Formulate Diameter and Roundness
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?
--
JHG
RE: Formulate Diameter and Roundness
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...