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Datum Reference Frame
Another Datum Reference Frame Tip  

   Datums Are Mutually Perpendicular - Even When the Datum Features Are Not.

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 55mm BASIC location would be measured from the third datum plane-not from the sharp point on the actual part.

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