2009 ASME standard

Another New Symbol in GD&T

Posted by on Dec 21, 2011 in 2009 ASME standard

If you’ve been keeping track of the new GD&T standard, then you’re probably aware of most of the bigger changes. (Yes, I know that 2009 doesn’t sound “new,” but most people still call it the new standard since it takes a while for companies to switch to a new dimensioning standard.) The new item I want to show you is pretty easy.  It is called the “all over” symbol, and it is very similar to “all around,” which may be familiar to you.  Both of these symbols will be found with feature control frames that use profile of a line or profile of a surface.   Here’s an example of the “all around” symbol, which has been in use for many years: The “all around” symbol is the small circle on the elbow of the leader line for the GD&T feature control frame.  This means that there is a profile zone imposed around the entire perimeter of the part, but only in the left-hand view. It doesn’t cover the two large faces of the part (this is why the 30 mm dimension still has a ± tolerance on it).  Here is the same “all around” profile zone shown in yellow:   OK, but now let’s look at the new...

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Non-Uniform Profile Tolerancing

Posted by on Feb 8, 2010 in 2009 ASME standard

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...

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A New “Feature” of the 2009 GD&T Standard

Posted by on Nov 11, 2009 in 2009 ASME standard

OK — time to dive into another item that is new in the world of geometric tolerancing.  The standard that was released earlier this year expanded the definition of a “feature of size.”  This has an impact in that some GD&T symbols can only be applied to “features of size,” most notably position. The 1994 standard defined a feature of size as a single entity: “One cylindrical or spherical surface, or a set of two opposed elements or opposed parallel surfaces….”  This is just a fancy way of describing things like a hole, pin, a part thickness, or other feature that can be measured directly for size. A traditional “feature of size” The 2009 standard now breaks “features of size” into two categories:  regular and irregular features of size.  The regular feature of size keeps the definition given above. The irregular feature of size is new: it is defined as “a directly toleranced feature or collection of features that may contain or be contained by an actual mating envelope….” Thus, a grouping of objects can now form a “feature of size.” This allows a geometric tolerance to be applied to the group as if it were one feature.  In the example below, I can position the imaginary circle with GD&T,...

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MMB — A New Term in the ASME Y14.5 Standard

Posted by on Jul 30, 2009 in 2009 ASME standard

If you are a regular user of GD&T, you probably know that the ASME standard was recently revised (for details, see the blog entry below dated March 28, 2009).   In today’s column, I’d like to introduce you to one of the changes. The term “maximum material condition” or MMC has been around for a long time. This concept is invoked when the circled M symbol is placed in a feature control frame.  Well, a new item for the 2009 standard is something very similar, called “maximum material boundary,” or MMB.   Yet it is invoked using the same circled M symbol. The reason this was introduced was to eliminate confusion when the M symbol is modifying a datum that has its own geometric tolerance. Consider the following example: The position tolerance references datum feature B with the M symbol.  But here’s the key: think about the size of a gage pin that would be inserted into the center hole (it should be attached to a flat plate that simulates datum A).  It would not really be simulating the MMC of 22.0; instead, it would be 21.8 in order to accommodate the perpendicularity tolerance of 0.2.  Thus the confusion — people would say “MMC” when discussing the datum, but...

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New Standard for GD&T: ASME Y14.5-2009

Posted by on Mar 28, 2009 in 2009 ASME standard

Well gang, it’s finally here!  The new standard for GD&T has been approved and will be shipping in the next week or two. If you’ve been around GD&T at all, you should be somewhat familiar with the 1994 standard; this new edition of Y14.5 will gradually be taking over as companies make the switch for new designs over the next couple of years. For those of you that were around when the 1994 standard was released, you may recall that there were many significant changes ranging from tweaking definitions to adding new symbols such as the triangular datum symbol (which was formerly a simple rectangular box).  This time there are similar changes, although most will not be as obvious as the change to the datum symbol was. We will be offering training in the new standard!  If your company needs a simple update on what’s new, contact us for information about the one-day New Standard class.  If your group would like a regular GD&T class, we can do that (3 days of training) and incorporate the new standard into the class as we teach the basic concepts. Copies of the new standard can be obtained through the publisher, ASME, at this website. Of course, remember that the change to the new standard cannot...

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