Pattern of holes as reference and function of frame with profile in a special condition

[roberto1brazil]

Hello everybody.
Please, I need your support regarding the sketch attached. It is a simplified drawing of a shroud of turbine. Only the main features are represented in the sketch. The aim of drawing is to supply information to machine a lobule located at 30° from hole “O” at opposite position ( section E-E). There is a fixture that locate the part 0,15 mm off center (in the angle indicated) in order to machine the internal lobule. The part is supplied with an initial internal diameter ranging from 237,65 to 237,70. The average wall thickness is around 1,45 mm. The origin reference center (B) is established by the three holes diameter 7 in the basic diameter of 282 mm.
In a practical way, the internal lobule is done moving the cutter to outside little by little until the thickness reaching near 1,3 mm thickness at position of section E-E. In fact it is done controlling the final thickness.
Doubts:
1- Why the reference B is written as B-B inside the frames?
2- What does it mean the frame identified with interrogation (?) in the sketch and what would be its function?
Thanks for any comments.

Roberto1brazil

 

[3DDave]

The disagreement is that you propose that 'size' applies to a cone and I know that it doesn't. An example of a 'size' isn't proof.

Here's one question - can a nominally 1.0 inch diameter rod fit into a nominally 0.5 inch hole regardless of length?

I'd say that it probably cannot.

Next question - can a 15 degree taper cone fit into a 15 degree tapered hole?

I'd say it can if the distances to their extents from the apexes of the two features have overlapping ranges, a claim that is true without measuring any local size.

Since a cone is defined by the taper, working to convert it to other coordinates that hide that fact simply confuse that size is irrelevant.

 

[Belanger]

I agree with your answers within your last comment, but that's not the topic I was challenging. Actually, you are describing the very thing that is an exception to my premise, if you'll read my post carefully (re: Figure 8-17).

To get to the root question, should a profile tolerance be applied to a basic diameter or not? If not, then I'll be asking you about the first several pix in my previous attachment.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems