How to Establish Conical Feature's axis as datum?
How to Establish Conical Feature's axis as datum?
(OP)
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.
(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.





RE: How to Establish Conical Feature's axis as datum?
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RE: How to Establish Conical Feature's axis as datum?
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.
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JHG
RE: How to Establish Conical Feature's axis as datum?
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
RE: How to Establish Conical Feature's axis as datum?
greenimi, drawoh, Thanks for sharing the details regarding ASME 2009 version. I'm discussing the possibility of incorporating the same in our drawing.
RE: How to Establish Conical Feature's axis as datum?
Also, can you explain how the conical surface is not a feature of size? Doesn't ASME Y14.5M-1994 define Conical tapers?
RE: How to Establish Conical Feature's axis as datum?
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.
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JHG
RE: How to Establish Conical Feature's axis as datum?
"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).
RE: How to Establish Conical Feature's axis as datum?
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?
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:
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