The datum reference frame establishes a shared set of orthogonal planes that is leveraged by all subsequent feature controls and tolerances that you specify. For now don’t worry about feature and target symbols, just know that datum features are associated with real parts and are not theoretical.ĭatum reference frame (DRF): A datum reference frame is three mutually perpendicular intersecting datum planes. In this case we’re talking about actual part features things like faces, edges and vertices. Putting aside the definition of the theoretical datum feature simulator for now, the important thing to remember is that datums are theoretically exact.ĭatum Feature: A datum feature is a feature that is identified with either a datum feature symbol or a datum target symbol. GD&T terminology can get tricky so let’s start with a few key definitions: datums, datum features, and the datum reference frame.ĭatum: ASME Y14.5 defines a datum as a theoretically exact point, axis, line, plane, or combination thereof derived from the theoretical datum feature simulator.
Datum reference how to#
Then we’ll use real part and assembly examples to demonstrate how to select the right datum features on your part to build a datum reference frame that communicates design intent and makes inspection setup simple and accurate. We’ll start by going over some of the basic terminology and definitions related to datums. Without a solid understanding of datums you won’t have the ability to construct feature controls that communicate your design intent. In this article, we’re going to focus on all things datum related in GD&T.
When applying GD&T the first consideration is to establish a datum reference frame based on the function of the part in the assembly with its mating parts. If you actually read ASME Y14.5-2009, the first important point made relates to the foundational concept of the datum reference frame. William Burke Five Flute Founder & CEO Motivation: Why Datums?
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