GD&T Clocking of Hex Cut-Out

[catiaUSR]

Hey Folks

I have tab with two cut-outs. One is a circle and and the other is hex shaped.

The design intent is:
[ul]
[li]to have the tab sit flush on the bottom surface (lower image is a top view)[/li]
[li]to have the hex cutout be aligned to the circle mid plane with a high tolerance ie up-down-left-right in the top view[/li]
[li]to clock the hex cutout, as in it's rotation about an axis out of the page formed by a true geometric counterpart of the greatest dia cylinder that fits in the hex, so that this is less important than the up-down-left-right described above and therefore has greater tolerance[/li]
[/ul]

Basically where the clocking of the hex is looser than the position of the center of the hex.

I've thought about a composite profile tolerance for the whole hex (fig 8-22 of Y14.5) but I'm not sure I can control just rotation about the right axis. And I've thought about selecting two adjacent faces of the hex and creating a PLTZF/FRTZF relationship but I'm not sure I can select just two sides of the hex as a feature.

Let me know what you think!

 

[AndrewTT]

what features are you using as your datums?

 

[3DDave]

I think there isn't a symbolic method to describe what you want to do in the order you want to do it. The test for that thought is to write out a note that describes the situation and then see if there are existing symbols to do what you want.

The alternative is to make the star the secondary datum for the hole and the boundary of the part and use the '2009 version to remove the angular orientation control from it. Refer to figure 4-46 of the '2009 for an example of eliminating degrees of freedom ordinarily taken by a datum feature.

 

[pmarc]

How about something like this?

http://files.engineering.com/getfil...1b2b-4c8a-af62-7bd319246eb1&file=clocking.PNG

 

[AndrewTT]

2009, 8.8 - Combined Controls (figure 8-24)

The profile tolerance gives you the size and shape. The position refinement gives you a boundary that the feature cannot violate. I believe this will give you more tolerance for the rotation of the feature than for the location. If you have a tight size tolerance on this feature then this might not work so well. Required basic dimensions are not shown.

My scan didn't show up well so I highlighted the part with the dashed lines for clarity.

 

[catiaUSR]

Wow. Kudos to pmarc and AndrewTT taking the time to write something up and upload it. Awesome.

AndreTT, that doesn't quite fit my intent because it doesn't differentiate the rotational DOFs. For the others..

So this was due Friday and I ended up going with something exactly like the suggestion from pmarc. I didn't know about just using the DIA symbol so I had to write a little note in words but now I know

But! I think the best answer is 3DDave's. I totally forgot about this. This would for sure work. Like you said, I'd setup FCF's for the circle and outer profile and just choose the out-of-the-page axis of the star feature when I needed. Sweet. Although my company doesn't use 2009 yet; so this will be an improvement down the road.

Thanks guys!