【转帖】surface profile with one datum reference - legal

yang686526

surface profile with one datum reference - legal?
i am a manufacturing engineer struggling with the interpretation of our design group as it seems they constantly push the boundaries of what my concepts of gd&t, and interpretations are.  as for the question...
i have a standard panel part with a thickness.  this part has several holes and a datum structure as follows.  datum -a- is a plane on the bottom surface.  datum -b- and -c- are hole features.  the remaining hole features are controlled to datums a|b|c with mmc respectively.  then i have an internal cutout feature that is basically an internal rectangle that goes thru the part.  this feature is controlled with basic dimensions but called out with a surface profile with respect only to datum -a-.  is this legal?  what is truly controlling the location of this surface feature if datum -a- is a plane perpendicular to the features surface.  hope someone can help with this one...
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joejack7
legal, yes.  useful.....doubtful.
controlling the profile w.r.t. "a" will control the shape of the cutout, but not the position or orientation.
it will only control the perpendicularity of the cutout wrt a, and i agree that it seems of little use.
even without any datum, surface profile would control the position and orientation within the boundaries specified in the fcf.  if the tolerance zone is small enough, it may be adequate.  it is more typical to have the feature fully datum-referenced.
jim sykes, p.eng, gdtp-s
profile services
cad-documentation-gd&t-product development
joejack,
i believe your cutout must have locating  dimensions and tolerances, and if size is basic dimensioned, it would require locating datum features.
ron
to use the surface profile, you need basic locating dimensions and size dimensions; you cannot use linear tolerances in conjunction with surface profile because you generate a potential conflict as to which one takes precedence.
jim sykes, p.eng, gdtp-s
profile services
cad-documentation-gd&t-product development