Another New Symbol in GD&T

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:

AllAround2

 

OK, but now let’s look at the new one, which is called “all over”:

Notice that there are two circles around the elbow of the leader line — this is a new addition in the 2009 standard (to get the same effect previously, we could have used a text note “ALL OVER”).   This means that the profile tolerance extends everywhere!  Notice that the depth dimension of 30 must now be a basic dimension.  Here is this new tolerance shown in yellow:

AllOver2

So as I said, it’s not a difficult concept. But be careful — all over literally means all over!  If there were any holes in this block, the profile tolerance would also cover the walls of the hole (which means the diameter of the hole would have to be given as a basic dimension).  So use this new one with caution.

10 Comments

  1. Hello,

    Is it possible to use this symbol to indicate the contour and depth of one particular pocket in a complex part? Or it can only be used to especify the whole part surface?

    Imagine that my complex part there are different pockets, and these pockets normally have a contour, depth and fillets. I would like to know if the ASME 14.5-2009 allows just one specification by part or several of the all over symbol

  2. Interesting question — let’s look at how the ASME standard defines it:
    By using the double-circle symbol, “a profile tolerance may be applied all over the 3-dimensional profile of a part unless otherwise specified” (paragraph 8.3.1.6).
    So I would say yes; the key is their mention of “unless otherwise specified.” You’d want to do something to “specify it otherwise.”
    You can use the symbol to control all surfaces of a pocket if it’s clear that the profile tolerance doesn’t spill over onto other adjacent surfaces. Perhaps you can still use the all-over symbol, but add a note beneath the feature control frame saying “shaded area only” (with shading or cross-hatching added), or “this pocket only” or similar.

  3. Can you have a U modifier without a value follow it? I.e., am I to interpret that the intent is the allowable tolerance zone is all “in”? Or, must it state 0 after the U?

    • Hello Jeff — according to the official rules, there needs to be a number of some kind after the U. (Yes, a zero would be all inward, but they should be showing the zero.)

  4. What about if I have a surface profile of:
    2.50 U 1.00 ABC

    What does this mean?

    • The first number is the total tolerance (the “bandwidth” of the entire profile zone). The U stands for unequal, and indicates that the 2.50 zone will be biased to one side a little (or entirely). The number after the U, in your example 1.00, would be the portion of the 2.50 zone that goes outboard. In other words, 1.00 is the tolerance amount that adds material to the CAD model, and the remaining 1.50 is the tolerance portion on the side that removes material from the perfect CAD model.

  5. Are all-around / all-over relent ONLY for the profile GCS?

  6. Is there a difference in saying profile all over .060 A|B|C. and profile all over .060. both stated with “unless otherwise specified”. Assume there are no refinements on any of the features that are used to establish datum planes

    • Yes, there would be a difference. Without the datum references, the all-over zone could be scooted around in a best-fit manner until it captured the actual surfaces of the part. But with datum references — even though those datums are derived from the surfaces being tolerance — the all-over zone would be locked in a specific location and orientation.
      Having the datum references would be much more restrictive, and you’d actually lose a portion of the tolerance zone on those surfaces that the datums are derived from.

      • In practice, how would a part get inspected if the zone can float? Say, on a CMM. Doesn’t a CMM require some origin from which to measure, and that is usually defined by the datum reference frame?

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