Reporting Profile given multiple points
Reporting Profile given multiple points
(OP)
As a standard rule, when given multiple inspection points taken via CMM or other method, how do you report the data to the customer? Do you report the worst case, the average or the range of data?
ie, if a profile of unilateral distribution is .006, and 9 inspection points are taken along the surface with results that range from .0016 to .0031 from nominal; do you report the maximum profile of .0062, the average profile of .0047 (averaging all 9 profile points), or the range of .0032 to .0062?
I can't seem to find a true standard, and I've always reported the worst case, but have recently found that others within my company report the average value, and some report the range of min to max. The way the profile is reported actually has an effect on whether or not the surface is reported as out of tolerance, so I want to make sure I get this right.
ie, if a profile of unilateral distribution is .006, and 9 inspection points are taken along the surface with results that range from .0016 to .0031 from nominal; do you report the maximum profile of .0062, the average profile of .0047 (averaging all 9 profile points), or the range of .0032 to .0062?
I can't seem to find a true standard, and I've always reported the worst case, but have recently found that others within my company report the average value, and some report the range of min to max. The way the profile is reported actually has an effect on whether or not the surface is reported as out of tolerance, so I want to make sure I get this right.





RE: Reporting Profile given multiple points
Range is better in most cases, stated as:
(Design Tol,I.E.; Profile sysmbol, Tol, Datums {Note Unilateral Outside/Inside}) 9 ea PT's on profile ck from +.0032 to +.0062.
Average is not acceptable, that would show your example as being with/in tolerance(.0047), when it is not(.0062).
RE: Reporting Profile given multiple points
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Reporting Profile given multiple points
Dave D.
www.qmsi.ca
RE: Reporting Profile given multiple points
Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Reporting Profile given multiple points
Thank you for all the replies which confirm my opinion that the average value does not reflect the true shape of the profile, especially given that one point is measured outside of the tolerance zone.
RE: Reporting Profile given multiple points
It occured to me that perhaps you meant the average absolute deviation, in which case the above would be 1/2" and not allowable anyways. However, I would still argue that a plate with one point at 1/2" thickness would not be acceptable, even if you had 1,000 additional points at exactly 1".
-- MechEng2005
RE: Reporting Profile given multiple points
An example that I've been working on with a supplier:
I have a R10 (basic) with a profile to a line callout of 0.2 (or a +/- 0.1 band). My individual readings are: 10.101, 10.105, 10.110, 10.113. My largest deviation from nominal of 10 is .113. Based on my understanding my actual profile is .226 or .113 X 2. I'm trying to explain this to a supplier but cannot find it in any GD&T books or in ANSI Y14.5. Is there something available that I can show the supplier?
RE: Reporting Profile given multiple points
There was an engineer from Hewlet Packard that insisted that producers and customers should address the profile reporting issue in a policy agreement between themselves because there wasn't any standard defined method and the most popular practice didn't work for some specifications.
He said their policy agreement method was to report the actual deviation from basic plus or minus where a plus value signified the deviation in a "more material" direction from basic and minus a "less material" direction from basic... therfore a plus deviation could make an ID smaller or an OD larger.
After trying unsucessfully to defend how I thought measurements in relation to un-equal bilateral or unilateral profile specifications could be presented as a doubled value from the "equivalent equal-bilateral basic reference"... I gave up and agreed with him. Their method is simple, accurate, universal(with regard to zone depiction), informative, and statistically friendly.
There is a group of volunteers addressing this and other measurement data reporting methods in a proposed new standard... but the bread is still baking.
Paul
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