Since it is a real entity, it is not exact and can have an irregular form.
#Datum reference frame professional#
One must be clear about both to make professional engineering drawings.Ī datum feature is a physical, tangible feature of the part that establishes the datum. Datum FeatureĬonfusing the terms ‘datum’ and ‘datum feature’ is a common mistake. Now, we can move on to more nuanced topics that will help you better understand the datum definition above. In this case, your datum will be the edge of the rectangle as that is the reference line you start measuring from. For this, you will have to measure the distance between the edge of the rectangle and the center of the circle. Now, you want to check how off-center you drew the circle. Suppose you drew a rectangle with a hole at its center. To further drive the point home, consider this very easy example. The datum symbol is compatible with all GD&T symbols except for those related to form tolerances (flatness, straightness, for example). Moreover, an additional piece of information is regarding its usage with other GD&T symbols. In easy words, a datum serves as a reference entity for measuring and locating the different geometric features of a part. A datum is an origin from which the location or geometric characteristics of features of a part are established.”
ASME Y14.5 (1994) defines a datum as “A theoretically exact point, axis, or plane derived from the true geometric counterpart of a specified datum feature. Let us begin by establishing a datum definition.
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