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Keep Control of Datum Features Simple (#40)

(In accordance with the ASME Y14.5-2018 standard)
(In accordance with the ASME Y14.5-2009 standard)
(In accordance with Y14.5M-1994 standard)

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Defining datums from a pattern of features can be confusing and there are many ways it can be done. On the part shown, it may be desirable to use two of the holes in the three-hole pattern as datum features. One approach would be to apply individual controls to each of the holes in the pattern as the first drawing illustrates. Another approach is to control the holes as a pattern using position relative to the primary datum, A. Then, label individual holes as datum features as shown in the second plan view. Depending on the tolerances and modifiers used, nearly the same control may be achieved with two less geometric controls, which simplifies the drawing and may simplify verification while meeting functional requirements.

Note: the drawing below is incomplete by intent.

This tip is in accordance with ASME Y14.5M-1994, Y14.5-2009 and Y14.5-2018.
This tip was originally released in February 2001.

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Back to Tips Tip added May 2021