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Make Certain You Have Controlled Your Datum Features!
(In accordance with Y14.5M-1994 standard)

PDF of this Tip

In most cases, datums are established from the extremities or high points of datum features. Measurements are then made from the true geometric counterpart of the datum feature. Consequently, datum features often do not get checked unless there is a tolerance that affects the datum feature. On the first drawing, the form (flatness) of datum feature A is controlled by the size tolerance of ±0.1 mm. It would not be necessary to add a flatness control unless the design requirement for flatness was tighter than 0.2 mm.

Back to Tips Tip added Aug 2003