huangyhg

datum reference frames fo composite tolerences
question: can you have the following callout? first tier - profile of a surface w/in .030 to a-b-c. second tier - profile of a line w/in .010 to a-b-c.
i believe that the second tierwould cancel out the top. please give me your thoughts.
tim martinez
anaheim, ca
check out our whitepaper library.
since you are calling out datums on the profile of a line tolerance, you are overriding the profile of a surface callout. with datums, the entire surface is being controlled by location (position) to the specified datums by the profile of a line callout. without datums, profile tolerances act as form controls. you could omit the datums on the profile of a line callout and have a valid callout.
marcelino vigil
gdtp t-0377
what we have is an extrusion shape. the entire surface needs to be w/in .030 to a-b-c and each section cut line of inspection points needs to be w/in .010 holding the same datum orientation but not locked to position. how would this be called out?
profile of surface w/in .030 to a-b-c
profile of a line w/in .010 to ?
which datums do we need to use to lock the rotation but allow it to move positionally?
thanks in advance,
tim martinez
profile of a surface is three dimensional while profile of a line is two dimensional.
i can see the possibility of profile of a surface to a,b & c which controls the shape and location of the surface and is usually perpendicular to datum a.
profile of a line is two dimensional and controls the shape of the shape and the location of the feature at its edge. one usually should never see profile of a line referencing three datums.
yes, one could see profile of a surface .030 to a,b and c while the second level is profile of a line .010 (component of profile of a surface) to b & c. (not datum a).

dave d.
tim,
what you are describing sounds like exactly what this gd&t tip addresses. go to this link and study what it says and it would be a good idea to bookmark the link too. there's a lot of good information there. from what i can see, there is no need for a "profile of a line" specification. just refining the lower tier as required while still using the profile of a surface callout.

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