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.

 

[Burunduk]

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.

If you are able to tell what result the runout measurement would yield assuming the surface is perfectly round but has a given location offset, then location is part of the runout control. It's a combined control and sure, you cannot immediately point the finger on the type of variation that caused the surface not to run true - and you don't always need to. But if there is locational offset (eccentricity) relative to the datum axis, it will affect the result of the runout control. There is no hand-waving around it.

 

[3DDave]

If you are able to tell what result the runout measurement would yield assuming the surface is perfectly round but has a given location offset, then location is part of the runout control. It's a combined control and sure, you cannot immediately point the finger on the type of variation that caused the surface not to run true - and you don't always need to. But if there is locational offset (eccentricity) relative to the datum axis, it will affect the result of the runout control. There is no hand-waving around it.

That's similar to explaining that flatness controls size. Can one thing influence the other? Sure. Many controls do. But runout of surface cannot uniquely determine the exact amount of location variation.

As soon as one depends on perfect conditions for some part of the problem why not depend on perfect conditions for the entire problem, rendering all tolerances moot? Oh, right, assuming perfect conditions is a bad faith argument to make.

 

[pmarc]

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?

greenimi,
That depends on what type of feature controlled by a runout tolerance we are talking about.

If we are talking about cylindrical features, then yes, I would agree that there is a location component in the runout control. However, even then, at least per the 2009 and prior versions of the standard, each feature controlled with a runout tolerance referencing the same datum feature(s) can potentially be evaluated in a slightly different candidate datum reference frame (for example, if the primary planar datum feature is a rocker).

On the other hand, if we are talking about planar faces nominally perpendicular to the datum axis, there is definitely no location component in the runout control, neither relative to the datum reference frame nor just between multiple features.

Long story short, runout is a tricky animal in this context.

 

[Gowthaman.D]

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.

Hello 3DDave and pmarc,

Thanks your explanation and time. I little differ from your answer. please correct my understanding is wrong.

Let take one example, there is coplanar surface, let we control the form of the surface. we can use flatness FCF with 2X and surface profile tolerance without datum along with 2X notation. how surface profile tolerance give common tolerance zone to the coplanar surface, surface profile tolerance also check it two surface individually right? why it's make common tolerance zone. here "nX" notation make sense it's pattern feature. If nX called it's controlling location and orientation relation between tolerance zones. Profile tolerance can control the size , form, orientation and location, reason why "nX" notation applicable to surface profile tolerance. since the flatness control only form of the surface, it can't control between tolerance zones relation, that's why "nX" notation not applicable to flatness tolerance.

There is question will come all surface flatness need to call individually. Answer is we can make it cut section view, below that number place mark it as "nX" its the best way to callout flatness for pattern surfaces. it will make sense to measure all the surface measure individually.

Hope, main reason to introduce the "INDIVIDUALLY" notation is to break the relation between tolerance zone when using "nX" on pattern feature to measure individually.

 

[greenimi]

Let take one example, there is coplanar surface, let we control the form of the surface. we can use flatness FCF with 2X and surface profile tolerance without datum along with 2X notation. how surface profile tolerance give common tolerance zone to the coplanar surface, surface profile tolerance also check it two surface individually right? why it's make common tolerance zone. here "nX" notation make sense it's pattern feature. If nX called it's controlling location and orientation relation between tolerance zones. Profile tolerance can control the size , form, orientation and location, reason why "nX" notation applicable to surface profile tolerance. since the flatness control only form of the surface, it can't control between tolerance zones relation, that's why "nX" notation not applicable to flatness tolerance.

There is question will come all surface flatness need to call individually. Answer is we can make it cut section view, below that number place mark it as "nX" its the best way to callout flatness for pattern surfaces. it will make sense to measure all the surface measure individually.

Hope, main reason to introduce the "INDIVIDUALLY" notation is to break the relation between tolerance zone when using "nX" on pattern feature to measure individually

I would say nX flatness with CF symbol is equivalent with nX profile with no datum.
Flatness (regardless if you use nX or not) does not have the power to control the relationship between features.
The pattern creation mechanism nX is only good with the callouts that are "powerful" enough to do the job you wanted.

 

[3DDave]

Let take one example, there is coplanar surface, let we control the form of the surface. we can use flatness FCF with 2X and surface profile tolerance without datum along with 2X notation. how surface profile tolerance give common tolerance zone to the coplanar surface, surface profile tolerance also check it two surface individually right? why it's make common tolerance zone. here "nX" notation make sense it's pattern feature. If nX called it's controlling location and orientation relation between tolerance zones. Profile tolerance can control the size , form, orientation and location, reason why "nX" notation applicable to surface profile tolerance. since the flatness control only form of the surface, it can't control between tolerance zones relation, that's why "nX" notation not applicable to flatness tolerance.

There is question will come all surface flatness need to call individually. Answer is we can make it cut section view, below that number place mark it as "nX" its the best way to callout flatness for pattern surfaces. it will make sense to measure all the surface measure individually.

Hope, main reason to introduce the "INDIVIDUALLY" notation is to break the relation between tolerance zone when using "nX" on pattern feature to measure individually.

Based on the 2018 definition, this commonality of tolerance zones only applies to position and profile tolerance zones. If the feature was a feature of size, such as a plate or a cylinder, then one could unify the multiple aligned surfaces that arise from grooves or ribs with <CF> / Continuous Feature. This is also not available to flatness.

nX applied to position and profile controlled surfaces is defined as creating a unified zone; if it is applied anywhere else, it does not create the zone. 2X .030 X 45º to create a chamfer, 2X OMIT PAINT, Weld-symbol 2X; in these, where n = 2, are allowed.

There are no other examples because Y14.5 is explaining why nX applied to the surfaces of a feature controlled by position and profile is an exception to all other uses of nX.

You can make up your own rules about this, but it's not necessary.

On a theoretical basis, one could never use flatness for a surface and only use Profile without any datum reference. Then it would make sense to use "INDIVIDUALLY" to ensure each component surface of an nX group is checked separately.

 

[Burunduk]

3DDave,
The 2018 version of ASME Y14.5 made it clear that the <CF> (Continuous Feature) symbol can be applied to any type of tolerance. This doesn't exclude flatness. They even added a separate definition for a Continuous Feature of Size beside the more general Continuous Feature.

 

[3DDave]

They did not define what an interrupted feature is.

Good to shine a spotlight on another gap in the standard. Thanks; educational as always.

 

[greenimi]

They defined the interruption.....Now, what is interrupted feature, maybe we can use the "analogy"....I don't know......

3.39 INTERRUPTION
interruption: a gap or gaps in a feature that divide it into two or more features (e.g., a slot or a groove).

 

[pmarc]

Hello 3DDave and pmarc,

Thanks your explanation and time. I little differ from your answer. please correct my understanding is wrong.

Let take one example, there is coplanar surface, let we control the form of the surface. we can use flatness FCF with 2X and surface profile tolerance without datum along with 2X notation. how surface profile tolerance give common tolerance zone to the coplanar surface, surface profile tolerance also check it two surface individually right? why it's make common tolerance zone. here "nX" notation make sense it's pattern feature. If nX called it's controlling location and orientation relation between tolerance zones. Profile tolerance can control the size , form, orientation and location, reason why "nX" notation applicable to surface profile tolerance. since the flatness control only form of the surface, it can't control between tolerance zones relation, that's why "nX" notation not applicable to flatness tolerance.

There is question will come all surface flatness need to call individually. Answer is we can make it cut section view, below that number place mark it as "nX" its the best way to callout flatness for pattern surfaces. it will make sense to measure all the surface measure individually.

Hope, main reason to introduce the "INDIVIDUALLY" notation is to break the relation between tolerance zone when using "nX" on pattern feature to measure individually.

Adding 2X in front of a flatness tolerance applied to a pair of nominally coplanar features does not make the features a pattern per Y14.5. In fact, the meaning of such a callout would ne no different than defining two separate flatness feature control frames - one for each feature.

If the two surfaces were controlled by a 2X profile tolerance, the pattern would be there by default (per the pattern definition). The INDIVIDUALLY notation, when added to the profile callout, would break the default pattern relationship into two independent tolerance zones.

The INDIVIDUALLY notation, when associated with a 2X flatness callout, would be redundant.

 

[greenimi]

Adding 2X in front of a flatness tolerance applied to a pair of nominally coplanar features does not make the features a pattern per Y14.5. In fact, the meaning of such a callout would ne no different than defining two separate flatness feature control frames - one for each feature.

If the two surfaces were controlled by a 2X profile tolerance, the pattern would be there by default (per the pattern definition). The INDIVIDUALLY notation, when added to the profile callout, would break the default pattern relationship into two independent tolerance zones.

The INDIVIDUALLY notation, when associated with a 2X flatness callout, would be redundant.

So what would be the difference between INDIVIDUALLY notation and SEP REQT (in the profile callout example you gave above)?

 

[3DDave]

They defined the interruption.....Now, what is interrupted feature, maybe we can use the "analogy"....I don't know......

3.39 INTERRUPTION
interruption: a gap or gaps in a feature that divide it into two or more features (e.g., a slot or a groove).

That's interruption, a different term. They could have said that a Continuous Feature unites feature separated by an interruption, but clearly they avoided using that and created a separate, undefined term.

In fact this is how "interruption" is used:

When a surface is controlled by a runout tolerance,
intended interruptions of a surface, such as keyways or
holes, do not affect the tolerance zone boundaries, and the
extent of the boundaries is limited to where there is
material.

In other words, just for runout, Continuous Feature is not required. Note that they don't distinguish between circular runout and total runout.

oddly:

interruption: a gap or gaps in a feature that divide it into
two or more features (e.g., a slot or a groove).

a keyway or a hole do not separate a feature into two or more features.

You and B. are a scent hound for finding flaws and defects in the standard - keep going.