ASME GD&T Certification Test - Converting Coordinate Tolerances to Profile Tolerances

optomist1

A Sea of Statistics
Super Moderator
Hi To All,

Does anyone recall whether there were any questions regarding converting Coordinate Tolerances to Profile Tolerances?? No specifics requested, I'd just like to know if this topic was covered on the exam.

Marty

Stijloor

Staff member
Super Moderator
Re: ASME GD&T Certification Test - Converting Coordinate Tolerances to Profile Tolera

Hi To All,

Does anyone recall whether there were any questions regarding converting Coordinate Tolerances to Profile Tolerances?? No specifics requested, I'd just like to know if this topic was covered on the exam.

Marty
Can someone with ASME GD&T Certification experience help with this?

Thank you very much!!

Stijloor.

D

David DeLong

Re: ASME GD&T Certification Test - Converting Coordinate Tolerances to Profile Tolera

Hi To All,

Does anyone recall whether there were any questions regarding converting Coordinate Tolerances to Profile Tolerances?? No specifics requested, I'd just like to know if this topic was covered on the exam.

Marty
I can't remember but it could be. You should know how to convert since it is easy.

If one had a tolerance of +/- .4 mm in one axis and +/- .3 mm in the other one, obtain the distance to the corner which would be the hypotenuse. In our case it is .5 mm. That is now the radial tolerance about true position. Now, double it and we get a diametrical tolerance zone of 1 mm. There, you have it.

Paul F. Jackson

Quite Involved in Discussions
Re: ASME GD&T Certification Test - Converting Coordinate Tolerances to Profile Tolera

I can't remember but it could be. You should know how to convert since it is easy.

If one had a tolerance of +/- .4 mm in one axis and +/- .3 mm in the other one, obtain the distance to the corner which would be the hypotenuse. In our case it is .5 mm. That is now the radial tolerance about true position. Now, double it and we get a diametrical tolerance zone of 1 mm. There, you have it.
David and Marty,
I would say that it may be possible to convert coordinate tolerances applied to non-features of size... if they were equivalently referenced from datum features declared on the drawing by some means either in a note or via dimension origin symbols... as those declared in the profile tolerance control.

It would not be possible however to convert RFS position tolerances because position controls the point, axis, or center-plane not the surface as profile does.

Likewise it would not be possible with other geometric controls that do not constrain parameters of the feature's form, size, and location like profile does... like runout, total runout, concentricity, and symmetry.

It is hard to imagine a profile tolerance being converted from a form tolerance because form tolerances don't have coordinates... but that does not mean that form tolerances cannot have an equivalent profile tolerance such as flatness (form tolerances applied to non-features-of-size).

As far as variable-limit tolerances are concerned (those features-of-size specified for position @ MMC or LMC)... they have coordinates (implied or specified) and they have boundaries for their size (virtual and resultant conditions now called their MMB max-material-boundary and LMB least- material-boundary) so I believe it may be possible ---as long as--- the position callout was specified "zero at MMC". The conversion would consist of basic dimensions defining the location of the feature from the DRF, basic dimensions defining the shape of the feature, and profile boundaries reflecting the MMB and LMB. Those position tolerances specified other than zero at MMC/LMC have unequal proportions for size and location and could not be equivalently bounded.

After thinking about it over night you cannot even do variable tolerances equivalently because a tolerance specified "zero at mmc" would have an LMC limit for size that is not equivalent to the resultant condition or LMB.

As I have said before… if one was to think of a profile in terms of a variable position tolerance you could think of it as a position tolerance that is both zero at MMC and zero at LMC, having its greatest liberty for location its form is perfect and it resides at its median location.

I wouldn't look for any of this variable tolerance conversion stuff to be discussed in any context having to do with Y14.5... these are my own musings. Also I would be surprised if there were any questions about converting coordinate tolerances to profile tolerances other than "It cannot be done" for the reasons I cited in the first couple of paragraphs.

I cannot remember what was on the test; it has been a long time since I took it.

Paul

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optomist1

A Sea of Statistics
Super Moderator
Re: ASME GD&T Certification Test - Converting Coordinate Tolerances to Profile Tolera

Good Day David & Paul,

Thank you very much for your assistance....I'll scan an example and post later this afternoon. Hopefully, this will provide a bit more insight...

Regards,
Marty

optomist1

A Sea of Statistics
Super Moderator
Re: ASME GD&T Certification Test - Converting Coordinate Tolerances to Profile Tolera

Thanks for the prompt....Stijloor

optomist1

A Sea of Statistics
Super Moderator
Re: ASME GD&T Certification Test - Converting Coordinate Tolerances to Profile Tolera

Hi To All,

Regarding my earlier post attached is an example problem....I get the concept and can translate Coordinate to Profile....just curious if similar type of problems were presented on the Technologist/Senior exam.

Marty

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Paul F. Jackson

Quite Involved in Discussions
Re: ASME GD&T Certification Test - Converting Coordinate Tolerances to Profile Tolera

Notice the prerequisite 1)Determine the datum features... limit tolerances do not typically have defined datum reference frames unless they are declared in a note or established by an origin symbol.

You can replace a limit tolerance with a surface profile tolerance applied to a non feature of size but it is not necessarily equivalent... The example you cited from Alex Krulikowski's materials uses the top surface as the datum feature... but he could have alternatively used the bottom surface as the datum feature.

Keep in mind that in the real world the surfaces are never perfectly parallel, using the larger would typically moderate the result and the smaller typically amplify it. I say tyypically because the three points determining the datum plane may not behave as predicted.

With the profile control one would expect that the inspection results would be more consistent because all would have measure according to the callout rather than choosing their own reference. I think that is Alexs' point in this illustration.

Paul

optomist1

A Sea of Statistics
Super Moderator
Re: ASME GD&T Certification Test - Converting Coordinate Tolerances to Profile Tolera

Hi Paul,

Thank you for the thorough response, I get it. Alex's/ETI's text is a great study guide, this together with the Y14.5M - 1994 text is my study guide.

I am just completing ETI's Advanced Concepts of GD&T....then study study study study......