Application of Rule #1 (Taylor Principle)
Application of Rule #1 (Taylor Principle)
(OP)
Given the following:

What is the tolerance on the Flatness of Datum Feature A?
a)The flatness is not toleranced.
b)0.3
c)0.5
d)1
Originally, I thought it was (a) because a +/- dimension is equivalent to taking a measurement with calipers/mic (meaning the only control is the width at any given point), so it would be possible for the part bow out and have a flatness greater than 1 while still having a thickness measurement of 24.5-25.5.
However, after re-reading over Rule #1 of the standard it seems that the correct answer is (d). If I understand it correctly, the application of the Taylor Principle to this problem means that the feature must fit within a perfect boundary of the part at MMC. In this case, the flatness on the feature could be as high as 1. Is this correct?

What is the tolerance on the Flatness of Datum Feature A?
a)The flatness is not toleranced.
b)0.3
c)0.5
d)1
Originally, I thought it was (a) because a +/- dimension is equivalent to taking a measurement with calipers/mic (meaning the only control is the width at any given point), so it would be possible for the part bow out and have a flatness greater than 1 while still having a thickness measurement of 24.5-25.5.
However, after re-reading over Rule #1 of the standard it seems that the correct answer is (d). If I understand it correctly, the application of the Taylor Principle to this problem means that the feature must fit within a perfect boundary of the part at MMC. In this case, the flatness on the feature could be as high as 1. Is this correct?





RE: Application of Rule #1 (Taylor Principle)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Application of Rule #1 (Taylor Principle)
Are you sure about that, J-P?
Have a look to attached graphic. The way I see it - even with the opposite side not perfectly flat the flatness error of considered surface may still be 1.0.
http://files.engineering.com/getfile.aspx?folder=f...
RE: Application of Rule #1 (Taylor Principle)
Actually, reading the original post, we don't know what datum feature A is -- it could be tagged with the size dim. But I suspect Sean meant that it was one of the faces, and either way the answer from the multiple-choice list is still d.
Sorry to muddle things with my extraneous comment :)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Application of Rule #1 (Taylor Principle)
Well, not exactly, J-P. Have a look to another graphic. (I assume that by saying "feature-of-size flatness" you meant "flatness of derived median plane of feature-of-size".)
http://files.engineering.com/getfile.aspx?folder=0...
RE: Application of Rule #1 (Taylor Principle)
How's that? :)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Application of Rule #1 (Taylor Principle)
RE: Application of Rule #1 (Taylor Principle)
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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: Application of Rule #1 (Taylor Principle)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Application of Rule #1 (Taylor Principle)
In ASME Y14.5-2009, see figure 2-6. They do not show the numbers, but it is pretty obviously answer d.
In ASME Y14.5M-1994, the figure still is 2-6.
--
JHG
RE: Application of Rule #1 (Taylor Principle)
Season
RE: Application of Rule #1 (Taylor Principle)
The datum is irrelevant to the tolerance specification. Calling up a datum was a good way to show us what surface he was referring to. It would have been clearer if the datum had actually been applied.
--
JHG
RE: Application of Rule #1 (Taylor Principle)
Frank