Another 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 2009 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 a copy of Y14.5-2009, you may read more about this in paragraph 8.3.2.
—–Amendment, showing the 2018 practice for this: ————-
Using GD&T-2018 How do you apply a non-uniformed tolerance without dashed lines?
Thank you,
Curt Bittner
Hello Curt,
Although the method shown is still allowed in Y14.5-2018 (paragraph 11.3.2.3), you’re correct that there is a new method to communicate a nonuniform profile tolerance.
The new way (paragraph 11.3.2) is to put two numbers in the feature control frame: the first number is the tolerance zone size at the beginning of the profile segment, and the second number is the tolerance zone size at the end of the segment’s run. A dash is placed between those two numbers.
The standard says that “the profile tolerance width is a proportional variation from one value to another between two specified locations on the considered feature.”
Then, beneath the feature control frame, an arrow pointing to the right is placed between the two letters of the segment start/stop.
I’ve added an snippet from the standard above, and if you have a copy of the 2018 version, then you can see a couple more examples as well.
How do you show non-uniform tolerance when you have a part that has no datums defined eg injection molded parts where we usually define zone tolerances. In your snippet there are 3 datums AB and C. Can I replace those datums and use zone method CZ as per ISO 1101
Hi — I don’t see why injected-molded parts wouldn’t have datums. There are parting lines, etc., so the functional datums might not coincide with what’s convenient on the tooling. But that aside, the “S” and “T” on that snippet could still be identified and used to establish the proportional non-uniform zone.
And regarding the ISO options, CZ can be a useful modifier (often for multiple coplanar surfaces) but that wouldn’t really speak to the non-uniform idea.