Surface Profile Callouts - How the profiles are being dimensioned

[brianq727]

Im not sure of how the profiles are being dimensioned here and what are the symbols with the mm <-> nn or xx <-> yy etc. I've haven't seen too many prints with these callouts on them. Someone please give me a brief explanation of what is going on here. I understand most of it but am just unfamiliar with these symbols.

 

[True Position]

Re: Surface Profile callouts

Im not sure of how the profiles are being dimensioned here and what are the symbols with the mm <-> nn or xx <-> yy etc. I've haven't seen too many prints with these callouts on them. Someone please give me a brief explanation of what is going on here. I understand most of it but am just unfamiliar with these symbols.

The mm <-> nn style callouts are the area of the part that callout is to. For the #71 dimension, the 0.020 Profile is for the surface between the corners labeled mm and nn.

 

[brianq727]

Yes I figured that was the case but how can the dimension be measured since it is tied to datum B and has no Basic dimensions??

 

[Jim Wynne]

Yes I figured that was the case but how can the dimension be measured since it is tied to datum B and has no Basic dimensions??

There might be a note on the drawing that says something like "CAD data is basic." This means that the expectation is that the part will be measured directly against a CAD model. This doesn't excuse the lackof proper dimensioning, but there it is. Also, those limit specs are superfluous, because the requirement would be the same without them.

 

[Miner]

Also, those limit specs are superfluous, because the requirement would be the same without them.

Not quite. The areas were the Profile call out is applied does remain the same, but the two sections (i.e., X-MM and NN-Y) are excluded from the call out.

 

[Jim Wynne]

Not quite. The areas were the Profile call out is applied does remain the same, but the two sections (i.e., X-MM and NN-Y) are excluded from the call out.

I don't see them as being part of the X-->Y surface. There's a definite tangent point between X-mm and Y, e.g.