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