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Datum - Repetitive Patterns
 

   Keep Identification of Datum Features Simple.

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 8 holes are located from datums A, B and C. A very cumbersome way to locate the 2X 4 patterns of holes relative to the 8 holes individually, would be to assign a different letter to each of the 8 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 8 holes are identified as datum feature D INDIVIDUALLY. Each pair of 4 holes has a position callout relative to A, D, B where D is the large hole nearest each pair. There are actually 6 datum D features. By using the INDIVIDUALLY note, the drawing is greatly simplified.

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