Profile without Datum reference

[AMontembeault]

Referencing this thread:

https://www.eng-tips.com/viewthread.cfm?qid=314750

It was discussed that a surface profile without a datum would essentially just be a form control on a singular surface. However, based on that discussion, I believe, based on the context of those discussions, that's true if we're talking about a surface which does not form a feature of size.

So suppose one were to apply such a control on the ID of a cylinder. Would the surface profile then control the size of the ID, or is it essentially just giving us cylindricity, requiring an additional tolerance for the size itself? What if the surface profile is not applied simultaneously to the entire ID surface, but rather in discrete segments (as to be measured with a radius gauge)?

I suspect I know the answer to these questions, am curious how others would interpret it.

Thanks

 

[chez311]

So suppose one were to apply such a control on the ID of a cylinder. Would the surface profile then control the size of the ID

Yes. The only way it wouldn't is if the new "dynamic profile" modifier introduced in Y14.5-2018 were applied.

What if the surface profile is not applied simultaneously to the entire ID surface, but rather in discrete segments (as to be measured with a radius gauge)?

If those segments are not controlled as a pattern (ie: nX instances) or utilized in conjunction with the continuous feature <CF> symbol and are less than 180deg/have no directly opposed points then technically no since size is not defined for features of this type (nonFOS).

 

[AMontembeault]

If those segments are not controlled as a pattern (ie: nX instances) or utilized in conjunction with the continuous feature <CF> symbol and are less than 180deg/have no directly opposed points then technically no since size is not defined for features of this type (nonFOS)

The old prints I'm working with specify "Any 45 degree segment", which is problematic because there are an infinite number of 45 degree segments.

 

[chez311]

I don't think thats an inherently problematic specification, though maybe a bit unusual unless the diameters are very large*. It would be akin to a straightness per unit length like in Y14.5-2009 fig 5-4 in the means this portion: "The derived median line of the feature's actual local size must lie within a cylindrical tolerance zone of 0.4 diameter for the total 100mm of length and within a 0.1 cylindrical tolerance zone for any 25mm length, regardless of feature size."

Note also that unless there is an overall profile or other tolerance applied to the entire diameter, you might be want to be aware of the greater amount of form/size tolerance that is possible when extrapolated around the entire ID. Without doing it out in CAD it is difficult to quantify.

*Edit - I should add that it is somewhat unusual also as thats not a typical application of profile though I should think it can be interpreted as to its meaning.