It is when the right hole has been produced at LMC. And another example is that of coaxial features we may have one diameter positioned to another diameter, and this “coaxiality” is indeed a location control. Assuming that all holes in the pattern have been produced perfectly perpendicular to datum plane A, and that the basic distance between the holes in the pattern is 2.000: MIN possible distance betweeen the axes of the top right and the top left hole is 1.990 2.000. ![]() One final footnote - there are times when a position tolerance may reference only one, perpendicular datum: If a pattern of features (two or more) are being positioned with one feature control frame, then a single datum plane is allowed (because there is the location between the two features that position controls). ![]() So it’s best to stick with the proper terms and symbols if you want to minimize confusion when expressing your requirements! The outside edges of the rectangular part are. But recall that the purpose of geometric tolerancing is to use a standardized language to express the design requirements. The only relationship being established between the two holes by GD&T is a straight-shot distance. Bi-directional True Position Multiple Single-Segment Method 2X 6 +. That said, there are no GD&T police that will haul you to jail if you insist on using the position symbol. Angularity (Feature Axis to Datum Surface) NOTE: Tolerance applies to feature at RFS. This is the correct way to identify this hole, since the hole itself now becomes the datum feature for other features to locate back to. Therefore, an orientation symbol must be used: The only relationship that the large hole has with datum A is one of orientation. Since the large hole given above is already distanced from the edges by plus/minus dimensions, the geometric tolerancing has nothing to do with location. There is a position tolerance applied to the large hole on the left, and the datum being referenced is A.īut let’s go to the standard and examine how the geometric control called “position” should be used: ASME Y14.5-2009 (and prior editions) state that position’s main job is to control location - meaning that it involves a distance - and perpendicularity often comes along as part of that position control. This is very common - it stems from some subconscious notion that if GD&T is going to be used on a hole, it’s got to be the “true position” symbol. It involves using the position symbol when the only quality being controlled is perpendicularity. ![]() This time around, I’d like to present another “pet peeve” of mine, at least in the world of GD&T.
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