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Keep Identification of Datum Features Simple - 1994, 2009, 2018 (#41)

(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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Frequently parts have repetitive patterns of features. Often it is desirable to use one of the features as a datum feature and control the other features in the pattern relative to that datum. On the part shown the 6X Ø8 holes are located from datums A, B and C. A very cumbersome way to locate the 2X Ø4 patterns of holes relative to the Ø8 holes individually, would be to assign a different letter to each of the Ø8 holes exhausting six letters of the alphabet. This awkward method is shown in the first drawing. A more efficient approach is illustrated on the second drawing. The Ø8 holes are identified as datum feature D INDIVIDUALLY. Each pair of Ø4 holes has a position callout relative to A, D, B where D is the large hole nearest each pair. There are 6 datum D features. By using the INDIVIDUALLY note, the drawing is greatly simplified.

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

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Back to Tips Tip added Jun 2021