Another new feature that was introduced in the 2009 standard (ASME Y14.5-2009) is the option of creating a “non-uniform” tolerance zone for either of the two profile symbols.
Recall that the profile symbols normally specify a uniform boundary or bandwidth that is centered around the “true” or perfect profile. This true profile is first established by basic dimensions on the drawing or by referencing the CAD model, which is the perfect design. Here’s a traditional profile callout:
where the tolerance zone looks like:
Notice that the 2 mm zone follows the exact contour of the intended design — this is how profile tolerances have always been understood, and will continue to be understood if no other indication is made. But the latest version of the Y14.5 standard allows a non-uniform zone, where the feature control frame simply says “non-uniform,” but it is then required that the zone be described in detail on the drawing or by referencing a note or other detailed information. An example:
Notice that each side of the tolerance zone has a different radius; the surface of the actual manufactured part can now deviate anywhere within these two curved planes. There may be various reasons why the designer wishes to do this.
I should also mention that the “non-uniform” profile usage may have a tolerance zone of any shape — it doesn’t have to always be a radial type as given here. Of course, if you have your new copy of Y14.5, you may read more about this in paragraph 8.3.2.
On an unrelated note, I can share with you that our training schedule is getting quite busy for the first half of 2010! Despite the recent economic woes, it seems that many managers are aware of the value in having all their engineers trained in the new standard. So if you haven’t already, please contact us to obtain a detailed proposal to have our seminar offered at your company.