If the feature of size is a cylindrical feature such as a hole in a part, the size value in the feature control frame is preceded by a diametric symbol to represent a circular or cylindrical tolerance zone. The position is most often referenced with two or three datum features to exactly locate and orient the true position. This means that you will have an exact point where the position should be with respect to a datum reference frame and your tolerance specifies how far from this you can be. When specifying a position tolerance, datum features are referenced within the feature control frame. The tolerance is a 3-Dimensional tolerance zone that surrounds the true position. Again, True Position is the exact perfect location of the feature, located and oriented to the datum reference frame using Basic Dimensions. Position in terms of the axis, point, or plane defines how much variation a feature can have from a specified exact true location. It can be used almost anywhere to represent any feature of size. When you have a hole in a part such as a bolt pattern, true position is usually called out. However, this can also be applied to any feature of size in need of a location tolerance, such as a pin, a boss, or even a keyway. In the image below you can see how a hole is called out using the position tolerance symbol. Position can be used with Max Material Condition ( MMC), Least Material Condition ( LMC), projected tolerances, and tangent planes. Locating surfaces is to be controlled via Profile. See the above central elements of a hole, slot and sphere. Position may be applied to any feature of size (Feature with physical dimensions like a hole, slot, boss, tab, or sphere) and control the central elements of these size features. For clarity on these two terms check out our article and video here.
However, it is correctly termed in the ASME Y14.5 standard as simply “Position”. Application:Īlthough incorrect, we title this page and sometimes refer to the symbol as “True Position” since this is typically the term people are referencing when they are looking for the position tolerance. However, since this is such a useful symbol, we will continue to add content and examples for other uses of this nifty little symbol in the coming months. The two methods of using Position discussed on this page will be RFS or Regardless of Feature Size and under a material condition ( Maximum Material Condition or Least Material Condition). Position is one of the most useful and most complex of all the symbols in GD&T. In other words, the Geometric Dimensioning and Tolerancing “Position” tolerance is how far your feature’s location can vary from its “True Position”. The “ True Position” is the exact coordinate, or location defined by basic dimensions or other means that represents the nominal value. I would think we will find a bond beam but I don't really know much about this stuff so I'm on a bit of a journey and having fun seeing what the SE comes up with.True Position, or just Position as the ASME Y14.5 standard calls it, is defined as the total permissible variation that a feature can have from its “true” position. It will also be interesting to see what is under the parapet wall roof caps. I am expecting the SE to be adding vertical reinforcements with grout to the walls to allow us to go up more courses, the walls are at about 14 feet right now. I would think the wall would come back down to its original position, allowing the head and bed joints to be knocked out a few at a time and repointed. It will be interesting to see that particular window blocked in and the lintel replaced. At least the walls are in great shape, minor step cracking in a few spots and one window has a steel lintel that swelled way up over the years and lifted one side of the wall above it by about 1/2 inch.
It is indeed running bond, the adjacent half blocks would get knocked out to allow a complete tie in with the new work and horizontal reinforcement can be added at that point if needed. I'll see what some local block suppliers have available too. If needed, the two layers of 4" blocks with ties and grout between is a great way to meet the old thickness perfectly. Sounds like there is not a structural issue with the slightly narrower blocks as I somewhat suspected. Looks don't matter much since it will have new interior walls covering up this work and the outside doesn't need to be fancy. Yeah, I certainly see the old bricked up windows that are slightly inset on older buildings.