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Datums Are Mutually Perpendicular - Even When the Datum Features Are Not.
(In accordance with Y14.5M-1994 standard)

PDF of this Tip

It isn’t always possible or practical to select datum features that are mutually perpendicular to one another when establishing a datum reference frame. Notice that datum feature C is not nominally perpendicular to datum feature B. The datum feature simulator for C would be made at 35° to the datum feature simulator for B (shown here in red). The actual datum planes (shown in blue), which comprise the datum reference framework, would however be mutually perpendicular to one another as is illustrated in the last figure. The deviation of the hole from the 55 mm BASIC location would be measured from the third datum plane - not from the sharp point on the actual part.

Back to Tips Tip added Jan 2001