Circularity on Metrology Software Question
Circularity on Metrology Software Question
(OP)
So Im trying to understand circularity and I thought I had a grasp on it until I see how some of my parts are measuring up in this metrology software. The picture shows a ring with a certain diameter and the only tolerance on there is the .035 circularity tolerance. The reading shows up at .016. The software is setup to show yellow lines when the tolerance is 75% or over. So the reading of .016 isnt even half of the tolerance. The reading at the point of yellow is about .010 off nominal. Does anyone understand how this could be showing up as yellow?





RE: Circularity on Metrology Software Question
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Circularity on Metrology Software Question
The dimensions indicate the circles represent the size limits and NOT the circularity tolerance. I assume the green and yellow "bars" represent the radial distance of the surface relative to an axis of rotation (center of the inspection device). You did not provide the "thickness" of the part, so I assume it is "thin" -a disc and not a pin.
First: Rule #1 is in effect here, so the surface can never be outside the boundary of a perfect form at MMC - a circle of 2.941. Many of the green bars extend beyond the 2.941 circle, which represents the perfect boundary, so Rule #1 is violated and the size is too large and also out of tolerance.
Second: The .035 circularity tolerance reduces the default 2.941-2.663 = .278 circularity error allowed by Rule #1 to two coaxial circles .035 radially separated. These circles "float" inside the boundary of a perfect form circle of 2.941 and get larger or smaller as the size varies. Again, I assume the two circles you show are size limits and not the .035 form error circles, which would be much "smaller" at the magnification shown.
One way to inspect the part NOT using a CMM, which would "automate" the verification:
1) the actual local size (micrometer readings) at every cross-section must be within size limits
2) the part must fit through a ring gauge with an inside diameter of 2.941 to confirm the surface is not outside the boundary of a perfect form circle.
3) a series of see-through Mylars (to accommodate different part diameters) with two .035 apart circularity circles is made. One at a time they are overlayed over the plot of green bars. The Mylar can be shifted around - no datums here. One of the Mylars must "capture" all of the outside edges of the green bars inside the coaxial circles. This confirms the circularity error. This technique is not viable at low magnification.
Hope this helps
Certified Sr. GD&T Professional
RE: Circularity on Metrology Software Question
Isnt the .016 measurement a combination of the high side and the low side? In this case, the circle is off perfect +.006 and -.010 which I can see makes the .016 reading. This software would change the actual reading dimension to show up yellow also if it was getting out of tolerance. So the .016 would show up in yellow as well as the area that is getting out of tolerance. I tested when the reading shows as a fail and it fails when the Circularity is toleranced at .028 but passes when its at .029 so I dont see how the .016 reading Im getting follows that reasoning because then it would fail once it got lower than .032.
RE: Circularity on Metrology Software Question
RE: Circularity on Metrology Software Question
What is the ".016 reading"?
What is the blue annular "ring"?
Why did the .035 change to .028?
Certified Sr. GD&T Professional
RE: Circularity on Metrology Software Question
Also, the software guys are jerks. Pale green on pale blue is tough to read.
RE: Circularity on Metrology Software Question
The .016 is the results of the measured data, its the circularity reading.
The blue ring is the tolerance limits set by .028 circularity test. So +/- .014 on each side of that test.
The the .035 changed because I wanted to find out when the software resulted in a fail. So .028 is when this data first failed.
What I am confused about is that I thought the data would fail once the measured data went beyond the blue tolerance boundaries. But its failing before that point so Im trying to find out if theres something about circularity that Im not understanding. The measured data is only .010 max off nominal on any side.
RE: Circularity on Metrology Software Question
I agree with 3DDave, contacting the softwate provider is definitely a thing to do.
RE: Circularity on Metrology Software Question
RE: Circularity on Metrology Software Question
RE: Circularity on Metrology Software Question
Now I know why I was confused. The software itself is confusing. I am used to FARO reporting, which is much more intuitive (assuming you know what Circularity is). So...I agree with the others. The software engineers do not understand what Circularity is and how to visually report in for ease of comprehension. Time to contact tech support.
Certified Sr. GD&T Professional
RE: Circularity on Metrology Software Question
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
RE: Circularity on Metrology Software Question
Certified Sr. GD&T Professional
RE: Circularity on Metrology Software Question
Regarding your second point, that warrants more explanation. I don't think I'm understanding you correctly.
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
RE: Circularity on Metrology Software Question
Yes, I was just expanding on you statement. I am not sure how much Vindicit knows about the intricacies of Circularity error.
Second: those unfamiliar with circularity control assume you can use a mic-check to inspect circularity error. Diametrical error equals form error - not the case. The diameter (size)can vary twice the specified form tolerance and still have acceptable form error.
Certified Sr. GD&T Professional