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 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:
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.