Profile trouble

[[Me...]]

I am having trouble getting a profile to read correctly. I am attaching a snip of the print. it appears that since Datum B is 2 surfaces that are at different angles that the surface KC1 will not profile correctly. any help with this will be appreciated.

[[De...]]

It is hard to say without seeing the definition of Datum B, if they are truly two surfaces that are not related to one another then they should not both be referenced as one datum feature. If they are something like two sections of a common plane or two sections of a common cylinder that would be ok, but not two unrelated features

[[De...]]

OK so actually, looking at the spec - I guess since it is acceptable to have a Mathematically defined surface as described in ASME Y14.5-2009 Section 4.13, there really is no way of saying that these two sections aren't two peices of a larger mathematically defined surface.

That said it also states..
"Where such a feature is specified as a datum feature, its datum feature simulator (derived from the math data) is used in establishing the datum reference frame. Aligning the high points of the datum feature with its datum feature simulator restricts movement of the part to the datum reference frame."

So sounds like an Outer Tangential evaluation is probably as close as your going to get, although to be honest I think this part should either have datum targets or else use a hard gage.

If I had to do this, I would probably create multiple 3D curves on both surfaces that would fully capture the surfaces, then I would use alignment to several curves to create an alignment using those two surfaces.

I would then create a theoretical feature that locked the degrees of freedoms that the datum feature would. So if the form of the two surfaces would lock only one rotation, then the theoretical feature should likewise only lock one rotation. Since Datum A locked some it should not be too hard to figure out what is left that B HAS to lock, and then make a theoretical feature that handles that.

Either way it would be a theoretical feature, that was tied to the alignment made in the previous step. This gives us a single feature that can now be used as Datum B.

I would name the theoretical feature Datum B and then use it in the profile call outs as Datum B.