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True Position v Legacy - Explaining to People.

MK1966

The above callout is on my drawing and it seems to be how our designers tolerance everything.
I need help explaining to designers about GDT in terms they can understand.
My datums have been generated using 3 generic planes with the correct vectors ie 1,0,0 / 0,1,0/ & 0,0,1 from 0,0,0, origin.
Sample below,
F1 =GENERIC/PLANE,DEPENDENT,CARTESIAN,$
NOM/XYZ,<0,0,0>,$
MEAS/XYZ,<0,0,0>,$
NOM/IJK,<1,0,0>,$
MEAS/IJK,<1,0,0>​
I can now calculate my true position for each individual hole.
​
If I use legacy dimensions without datum ref I have to use ±0.125
​Is this the correct way to do this​.​
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  • Whilst I like Neil's idea (sticking it to the designers!) I'd probably take a different approach.

    We don't know what the parts are, but it's possible (and although not technically valid anymore as far as I'm aware) there may be implied datums - i.e. if all/most dimensions are struck off one face or bore then we could say this was an implied datum and use that. As for datum order of precedence we could make an educated guess.

    As you likely know your parts, and what they do / how they assemble you could probably make an educated guess.

    So rather than a somewhat belligerent approach, you could actually do your best to confirm whether these parts will assemble and function as intended (even though that's incorrectly specified).
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  • Whilst I like Neil's idea (sticking it to the designers!) I'd probably take a different approach.

    We don't know what the parts are, but it's possible (and although not technically valid anymore as far as I'm aware) there may be implied datums - i.e. if all/most dimensions are struck off one face or bore then we could say this was an implied datum and use that. As for datum order of precedence we could make an educated guess.

    As you likely know your parts, and what they do / how they assemble you could probably make an educated guess.

    So rather than a somewhat belligerent approach, you could actually do your best to confirm whether these parts will assemble and function as intended (even though that's incorrectly specified).
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