Datum feature symbol placed directly on a planar surface.A dashed leader line indicates the far side surface. Point with a solid or dashed leader line with the datum feature symbol placed on it.Datum features can be either a surface or a feature of size, depending on how the symbol is applied. It is important though that datum features are indicated correctly on the drawing to ensure that the right type of feature is being controlled. Īs stated before, datums can be points, axes, lines, and planes or a combination thereof. A feature control frame will reference as many datums features as necessary to lock in all the necessary degrees of freedom, th is creates what is known as a Datum Reference Frame. This letter will also show up in any feature control frame that uses this datum feature as a reference. These letters are in boxes and tied to the datum feature s with a black triangle. The datum features on a drawing are denoted with a series of capital letters.
How Datum Features are Shown on a Drawing They are usually important functional surfaces. ĭatums are theoretical and only simulated by Measurement Equipment (Gauge pins, Granite slabs, angle plates, computer-generated planes, etc)ĭatum Features are real, tangible features on a part where the measurement equipment would physically touch or measure. It is especially important to know this when studying the theories of GD&T and while setting up a Datum Reference Frame. While they are related to one another they are indeed different entities. Its important to know the difference between Datum Features and Datums. It is usually an important functional feature that needs to be controlled during measurement as well.Īll GD&T symbols except for the form tolerances ( straightness, flatness, circularity and cylindricity ) can use datums to help specify what geometrical control is needed on the part. They are the surface or feature where the other features are referenced from. You can think of them as anchors for the entire part. A datum feature is the tangible surface or feature of size ( comprised of multiple surfaces or revolved surfaces) that is indicated by the datum feature symbol. Datums are theoretically exact points, axes, lines, and planes or a combination thereof that are derived from datum features.
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