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Select Your Datums Based Upon Function - Not Production
(In accordance with Y14.5M-1994 standard)

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Often production complains about the datum features selected. In general, datum features should be selected based on function-not on how the part will be produced. Two datum reference frames are used on the part shown below. The datum reference frame established by datum features A, B and C was selected because these are the features that locate and orient the bracket. From this datum reference frame the features used to locate and orient the module are located. The auxiliary datum reference frame D, E, A could then be established to position the four mounting holes. This approach to selecting datum features is functional and will usually result in the least variation in the assembly at the lowest cost. It is then up to production to use their skill, knowledge and expertise to produce an in-spec part. Besides, most Production folks will tell you they really don’t want the Design folks telling them how to make parts.

Back to Tips Tip added Feb 2004