GD&T - Concentric circles

[htjames]

Hi,

I am trying to show that two parts with semi-circles come together where the semi-circles are concentric and the profile of the semi-circles matches each other (same diameter). The semi-circles do not have the same arc-length, however and the parts themselves are different overall sizes.

How do I correctly GD&T this?
So far, I was thinking of using "concentric" or using "profile of a surface."
My research showed me concentricity being used on parts and only showed the side view (whereas my parts are shown looking directly at the circles).
What is the correct way?

Thank you

 

[Tenkan]

call out the two diameters position as if they were one thru hole is all thats needed.

lightweight, cheap, strong... pick 2

 

[pmarc]

If you are in ASME world, forget about concentricity. It requires diametrically opposed points on toleranced features and you will not find many, if any, in your application. For the same reason I would not go with position tolerance as it requires finding actual mating envelopes of both features which can be found in a repeatable manner only if the features contain opposed points or can collectively generate "closed" envelope.

That being said, profile of surface is what I would probably recommend in this case.

You can also have a look at following Tec-Ease tip:

http://www.tec-ease.com/gdt-tips-view.php?q=147

 

[powerhound]

I agree with pmarc. Profile of a surface may be your best bet.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Tenkan]

I totally agree with forgetting about concentricity.

Profile of a surface may be your best bet.

I've learned a lot from this forum, so maybe a little more here...
I understand profile of a surface also controls position, but it controls a whole lot more and that is that much more to inspect to. Why doesn't only position suffice?

Also, the way I see the OP's attached example drawing is its a weldment and the two items circles are positioned to each other within the same tolerance. The thickness of the combined thicknesses isn't really that thick, so is it really necessary to control the surfaces of the two... (and now one surface)? Maybe I'm missing something here but I see the cutout as a clearance feature... the weld fixture should be able to control both items in place sufficient for proper positioning. Couldnt the final drawing show the feature as one part, since its a weldment? Also, if the diameters really are a clearance feature then couldn't they simply be positioned without GDT to X and Y tolerances? It looks like a sheet-metal part with a stiffener/support feature welded on. It also looks like the hole (radius actually) is offset enough so that the center is not on the same position as the edge of the part. Again, maybe I am missing something on the design intent, but isn't Profile of a Surface a much more expensive way to control the feature?



lightweight, cheap, strong... pick 2

 

[powerhound]

Position can only be applied to features of size. Neither of the arcs are a feature of size. This is why position cannot be used. Note that this is per ASME Y14.5. ISO may not be the same way.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II