Position tolerance, Double-D Hole

[thepete]

See picture above(which hopefully posts)

I'm trying to use GD&T (Y14.5-2009) to tolerance the flats of the D-hole. What I'm trying to describe is the flats centered on the 1.125 diameter hole.

I also have to do something similar with the shaft that fits through this hole.

Position tolerance I have doesn't feel quite right. What are your thoughts?

Thanks,
Pete

(apologies to those who've seen this in a different (wrong) section of the forum.)

 

[fsincox]

I suspect the people who do not want to check my short pilot diameters for squareness are not going to like checking B & C for squareness to A here either.
Frank

 

[pmarc]

You are out because of lack of pain or something else?

I once asked 10 different inspectors: "For a simple rectangular block, where bottom face is datum feature A and flatness FCF controls its form, how would you verify this requirement?" You know how many answered something like: "You put the part on a base plate upside down, probe the datum feature with a height gage, and report the absolute value of indicator reading"? 8 of them.

This really is a problem out there in the real world.

 

[fsincox]

pmarc,
I think that is OK as long as it is good, right?
Frank

 

[pmarc]

But how to know that it is good if verification method is wrong?

 

[fsincox]

If it is good it is parallel and flat, is that not true?
Frank

 

[pmarc]

The surface is primary datum feature, so it does not have to be parallel to anything. The opposite face may be controlled for parallelism to it, but this check is not required if not explicitly stated on a drawing.

The inspection method described unnecessarily verifies parallelism - that is first thing. Second, it is not able to extract actual flatness error from this check.

 

[thepete]

To pmarc's points - this tab (bottle opener?) gets welded into a frame, rather uncritically. The hole location isn't that critical either... The Double-D itself is an anti rotation mechanism (for a fire hose fitting that I am concurrently working on) - so the hole itself is the only real critical thing here. The effort of inspecting the flatness of B and parallelism would be unnecessary unless it was so butchered that you could see it from across the street.