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Conversion of orthogonal tolerances to round tolerance zones

Conversion of orthogonal tolerances to round tolerance zones


TLDR: How should I use G,D T to show a square/rectangular tolerance zone around the FOS regardless of the shape of the feature?

Simple scenario: a hole is dimensioned using a +- tolerance scheme and say the X, Y locations are (10+/-0.25, 12+/-0.25). Now, if we apply G,D and T to this, we can convert this to a circular tolerance zone with a radius of 0.25*sqrt(2)=0.35, or dia 0.7 thereby gaining more tolerence. My question is - have we made the implicit assumption here that the designer made an oversight here i.e. he could've gotten away with more tolerance (0.7) than he toleranced the position of the hole at.

What if he really wanted the orthogonal position tolerances? i.e. he chose the tolerances after considering tolerance stack-ups along the two axes. Moreover, what if the tolerances were more in one axis than the other? I've seen some G,D,T reference books which have a chart for converting the coordinate measurements to round tolerance zones even if the tolerances in both axes are not the same. I found this confusing and I feel like I'm missing something here.


RE: Conversion of orthogonal tolerances to round tolerance zones

If you have access to Y14.5-2009, you may want to take a look at fig. 7-28 (in Y14.5M-1994 it is fig. 5-41).

RE: Conversion of orthogonal tolerances to round tolerance zones

Perfect! Much Thanks!

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