How to Establish Conical Feature's axis as datum?

[Jebin Tony Raj]

Hello everyone,

(Please refer the attached file)I want to establish the conical feature's (center portion) axis' perpendicularity with respect to datum A and then make the same feature as the datum B. how can that be accomplished in accordance to ASME Y14.5M 1994?

Thanks,
Jebin.

 

[greenimi]

http://www.geotolmeadows.com/newsletters/2009/nov2009.htm

Scroll to Subject: Conical surface as datum

 

[drawoh]

Jebin Tony Raj,

ASME Y14.5M-2009 Figures[ ]4.44 and[ ]4.45 show cones being selected as datum features.
The standard explains what all means. Note the very accurate profile tolerances. I cannot find the equivalent figure in ASME Y14.5M-1994.

If this were my drawing and the cone was not precise, I would apply a datum target at some arbitrary elevation from the datum[ ]A face. See figure[ ]4.52 (4.36 in the 1994 standard) on how to do this. That way, I define the centre. Perpendicularity would not mean anything to me, but I think runout would control it.

--
JHG

 

[pylfrm]

Jebin Tony Raj,

A conical surface is not a feature of size, so it does not have a feature axis in the ASME Y14.5M-1994 sense. A perpendicularity tolerance applied to the conical surface would not be valid.

There are various ways to achieve something similar to what you describe though. Can you describe the functional requirements of the part? That may help determine the best approach.

You can make the conical surface datum feature B by attaching a datum feature symbol to it, just like you have done to make the flat surface datum feature A. Be aware that datums and datum features are two different things.

The datum(s) derived from datum feature B will depend on how it is referenced in tolerances. How do you intend to do this?


pylfrm

 

[Jebin Tony Raj]

Thank you all for your replies.

greenimi, drawoh, Thanks for sharing the details regarding ASME 2009 version. I'm discussing the possibility of incorporating the same in our drawing.

 

[Jebin Tony Raj]

@pylfrm, I intend to establish the axis of the conical feature at some gage point and use it to control the profile of surface of the other conical feature at the left end which will be machined for further mounting of components. This part is a simplified version of a casting.

Also, can you explain how the conical surface is not a feature of size? Doesn't ASME Y14.5M-1994 define Conical tapers?

 

[drawoh]

Jebin Tony Raj,

Your cone has a diameter (somewhere) and an angle. The one shown in ASME Y14.5-2009 is defined by a profile tolerance, not just a simple [±][ ]dimension. Thinking further on Figure[ ]4.44, I would not specify the height to my datum target. I would specify an arbitrary diameter. This would simplify gauging.

--
JHG

 

[greenimi]

In ASME a conical surface is not a feature of size because it is not
"one cylindrical or spherical surface, a circular element, and a set of two opposed parallel elements or opposed parallel surfaces, each of which is associated with a directly toleranced dimension." (definition of the regular FOS)

Also, cones do not fit the definition of irregular FOS either --that may contain or be contained by an actual mating envelope that is / (other than) a sphere, cylinder, or pair of parallel planes

However, ISO treats cones as a FOS (so, you can use position to locate its axis). In ASME you have to use profile for this task (location).

 

[pylfrm]

I intend to establish the axis of the conical feature at some gage point and use it to control the profile of surface of the other conical feature at the left end which will be machined for further mounting of components.

You can't very well establish an axis from a single point. Do you intend to use the entire conical surface, or only a limited portion of it? If a limited portion, what are the specifics?

Do you intend to use the conical surface as a primary datum feature reference? If not, what datum feature(s) will have higher precedence? Which degree(s) of freedom do you want to constrain?

Also, can you explain how the conical surface is not a feature of size? Doesn't ASME Y14.5M-1994 define Conical tapers?

The ASME Y14.5-2009 definition for regular feature of size was already provided by greenimi, but the 1994 version actually makes things even simpler:

1.3.17 Feature of Size. One cylindrical or spherical surface, or a set of two opposed elements or opposed parallel surfaces, associated with a size dimension.

However, I realized that my earlier statement is rather misleading. The standard does not say that something must be a feature of size to have a feature axis. It does define feature axis in a way that's not compatible with conical surfaces though.

pylfrm