nX / nSURFACES notation can be used for all the GD&T character?

[Gowthaman.D]

Asper ASME Y14.5 nX notation used to applied for position and profile tolerance controlling group or pattern feature. many of the drawing now i am seeing nX used for flatness / parallelism. it's all applied to individual feature not pattern or group feature. Refer ASME Y14.5 2009 section 1.3.42 pattern requirement. even no where in standard used nX notation except the position and profile explaination. Using nX notation to Flatness and parallelism is right callout? can you please give your view on this.

 

[3DDave]

Is the drawing requirement unclear?

Is there some way that you cannot tell which surfaces the flatness and parallelism is being applied to?

Is there some other notation that you think is the correct one to use or is the expectation that each surface have a separate Feature Control Frame applied for flatness or parallelism?

Y14.5 examples are only the limited set of things they are concentrating on and in no way are they concerned with anything else. There are significant numbers of loose ends that are left to the individual creating documentation to do whatever they feel is best. If they are trusted to make all other decisions about the design they should be trusted to handle cases that Y14.5 ignores.

 

[pmarc]

It is OK to use nX/n SURFACES for form, orientation, and runout tolerances.

The thing to remember, though, is that unlike for position and profile tolerances, the nX/n SURFACES notation applied to form, orientation, and runout does not create a pattern of tolerance zones. That is, each tolerance zone shall be considered independently.

 

[3DDave]

The same applies to using "n SURFACES" to control the application of paint, plating, surface hardening, surface finish, et al.

Note that there is no exception mentioned for calling something a pattern when, for example, the note "SEP REQT" is applied to the Feature Control Frame for "n" holes. In such cases, there remains a pattern defined even though the members are considered independently.

I would expect that, in the next revision, rather than changing to the term "related group," which would apply to the members of a pattern that aren't noted "SEP REQT" because they automatically share a common datum reference scheme, the basis of a related group, that the misuse of the term "pattern" will continue and add yet another to the lengthy list of qualifiers. There is no common use of the word "pattern" to refer to elements that have no resemblance to each other and are not repeated multiple times, unlike what the Y14.5 definition allows for.

My expectation is because between 2009 and 2018, the committee changed from:

pattern: two or more features or features of size to which a locational geometric tolerance ... (not position tolerance??)
to
pattern: two or more features to which a position or profile geometric tolerance is applied and that are grouped by one of the following methods
noting the substitution of " position or profile geometric tolerance" to patch the gap left by "locational geometric tolerance".

 

[greenimi]

It is OK to use nX/n SURFACES for form, orientation, and runout tolerances.

The thing to remember, though, is that unlike for position and profile tolerances, the nX/n SURFACES notation applied to form, orientation, and runout does not create a pattern of tolerance zones. That is, each tolerance zone shall be considered independently.

pmarc,

The "one" that bother me is the runout.
I understood that form and orientation tolerances CANNOT create a pattern because "they" don't have a power to locate anything, but runout does have a power to locate features between each other hence runout should not have been part of the "not" creation mechanism.
(runout= position/location "plus" form error--at least at the cursory level)

Do you agree with my assessment?

 

[3DDave]

Runout is a form tolerance. It cannot distinguish between a perfectly circular surface that has a location offset and an oval surface that is perfectly located when both yield the exact same measurement.

Runout presupposes a location and measures only variation in form from it. For each individual point on the surface, runout provides no location control. It's only a measure of the dispersal of radial measurements, not of the value of the individual measurements.

 

[greenimi]

Runout presupposes a location and measures only variation in form from it. For each individual point on the surface, runout provides no location control. It's only a measure of the dispersal of radial measurements, not of the value of the individual measurements.

Fig 12-6 /2018
"Location of circular elements" and "Location of entire surface" has the check mark on circular runout tolerance and total runout tolerance respectively.
So I don't know why you are saying that "runout provides no location control". You might be right, but the difference is so subtle that I am not understanding it.
Is it a difference without distinction?
Otherwise I can tell you that I am lost here.

 

[3DDave]

I am not held by the justifications made by the committee. What they say is incorrect.

Runout controls radial location the way that flatness controls linear location - they don't. Flatness is the same as runout when an infinite radius is reached. Circular elements are mapped to straightness which also does not control linear location.

This is what happens when people redefine common words to mean things other than they do everywhere else.

They record variation in surfaces, not location of surfaces.

Maybe by 2058 there will be a version where the committee comes to its senses, but of course, that's about 100 years of being wrong and cannot expect them to deny tradition.