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Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?
3

Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
In fig. 6-30, what tolerance controls the length of the threaded M42 section?
There are basic dimensions 22 and 32, however while basic dimension 32 is clearly related to the general profile tolerance since there is a step there that is part of a true profile, I'm not sure what to make of basic dimension 22. It is given to where the basic diameter 36 ends and the thread starts, but is the true profile and the general profile tolerance zone well defined at that place? Part of the problem as I see it is that there is no step there to take part in a clear true profile (basic dia. 36 is only slightly smaller than the minor dia. of M42).

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Could you, please, have a picture attached? Not everyone has access to the document.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)

greenimi, this is the figure.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Figures in the standard are incomplete by intent. That portion of the figure and the applicable chamfers are not well defined.
I would read that 10 basic dimension (32-22) is the length of the full formed thread. But it is just me.
To complete a little bit more this figure maybe a note such as "CAD is nominal" or "refer to the CAD model for incomplete definition, basic CAD per model#######" or an equivalent note.

Let me ask a related question: do you think that the general profile is applicable to the 31.6- 31.8 outside diameter?

I think it does. But I am sure it is not clear.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
greenimi, good point about figures in the standard being generally incomplete, but this specific one - I think that other than the bit about the true profile behavior at the start of the thread (and chamfers as you mentioned), looks to me quite fully defined, isn't it?
Out of curiosity - suppose that the CAD model is not intended to be part of the definition, how would you suggest completing the missing piece?

To your question, I don't think dia. 31.6-31.8 is controlled by the general profile tolerance, as the general tolerance applies only to surfaces the variation of which are not "otherwise specified", whereas the size, form and location of the feature are fully defined by the size and runout tolerances.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Burunduk,

Lets ignore the actual thread form for a moment - you're not actually concerned where the thread helix itself starts/ends as the implication as I read it is that the indicated area is fully threaded. Trying to control the start/end of the thread helix itself on features which aren't fully threaded is a bit more difficult and tight control over which requires specialized gauges - its usually best to allow for looser tolerances here when possible (blind tapped holes, screw threads where the shank is not back-cut, etc..) and/or specifications like "min thread depth", "max incomplete thread" or a length where no threads are acceptable.

What you're actually asking is the tolerance on the location of the chamfer of the back cut/tapered portion. A quick scan of some thread standards seems to indicate that the leading/trailing chamfers aren't strictly controlled by your thread definition which makes sense because this can be modified for different purposes even with the same thread form (ie: MAThread or various self-tapping threads though some of these might also have proprietary/custom thread forms). Would you disagree that if a basic (or in your example, either basic or undimensioned) angle is added at each end of the threaded portion that this is fully defined? I'd probably recommend a directly toleranced distance/angle if this location/angle is not extremely critical in most applications though.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Burunduk,

As noted above, ASME probably did not care about a complete drawing.

On a real drawing, there should be a note somewhere specifying tolerances for dimensions based on the number of decimals. This would control those tolerances.

Any time I have designed part like this, I specify the distance between the end of the thread and the shoulder. Presumably, I want to screw something down accurately, all the way to the shoulder. I specify the maximum distance. I don't care what the minimum distance is.

I am taking this way too seriously. Greenimi is correct.

--
JHG

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
Thanks for the input, guys.
chez311, I agree that if basic angles are added at both ends of the threaded portion this drawing becomes fully defined, and the length of the threaded portion becomes controlled by the general profile requirement, but I am not sure how inspection-friendly this is. I get why you suggest a directly toleranced distance to one of the ends of the threaded portion. drawoh's suggestion seems to be on the same line.

Interestingly,  the version of this figure from the 2009 edition of the standard had all the distances in the axial direction directly toleranced (see the image below). Most of those distances were non-size dimensions. I guess the committee's objective in changing the scheme to basic dimensions and a general profile was to further demonstrate that location dimensions shouldn't be directly toleranced. But would you guys disagree if someone raised a concern that the newer version  of the part design is costlier to inspect (relative to the older one below)?


RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Quote (Burunduk)

But would you guys disagree if someone raised a concern that the newer version of the part design is costlier to inspect (relative to the older one below)?
Yes, I would (disagree).
You can measure the applicable profile WITH a caliper, but you would just have more uncertainties, which uncertainty is "un-escapable" -all measurements methods are subject to it (some of them more and some of them less)

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

I agree with greenimi regarding profile vs. directly toleranced dimensions.

Also, I think that addition of basic angles at both ends will be enough only if the drawing is clear that the nominal height of the slopes at the ends is the same.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
pmarc, greenimi, 
I also think that in most cases, profile of a surface is not the expensive requirement many still consider it to be, and often can be verified with relatively simple metrology equipment. Especially when the tolerance is loose, and the measurement uncertainty is less significant, as in the case of a general profile note.

But (speaking of verifying profile with a caliper...), could the 36 basic diameter in conjunction with the general 0.5 profile tolerance be more stringent than a direct tolerance diameter of 35.75-36.25, because the former requires perfect form at LMC, while the latter does not?

pmarc, I now see how the addition of basic angles at both sides alone does not fully define the geometry. This is how I think that a full definition in the first figure (from the 2018 edition) could be achieved:  The true profile on the left side could be defined by the basic 36 diameter, the basic distance 22 (which is given to the internal theoretical corner), and a basic angle which would be added. On the right side, the true profile is defined by the basic 32 distance locating the step, and the additional thing required would be the chamfer size between the thread and the step. The drawing notes could tell what the unless otherwise specified internal corner radii and external chamfers should be, with a direct tolerance. Does that seem OK?

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Burunduk,

To answer your first question, it depends on what you mean by more stringent. It is true that the way the 36 diameter has been toleranced in the 2018 figure requires perfect form at LMC, but on the other hand notice that the general profile of 0.5 creates tolerance zone boundaries that are 35.5 and 36.5 in diameter, which means that the size tolerance is doubled compared to the 2009 figure.

Also, I think the change they introduced in 2018 regarding the tolerancing method for the 36 diameter is of different nature than the changes for the axial dimensions. As you pointed out in your initial post, the axial dimensions were changed to support the argument that non-size dimensions should not be directly toleranced. But in case of the diameter, they simply fixed the error made in the 2009 where a geometric tolerance of location was simply missing. And they chose general profile to fix this. So I wouldn't really try to compare the two figures in that aspect.

Regarding the second question, I would probably just add another basic diameter on the right side where the chamfer starts.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
pmarc, that's a great input.
I suspect that there might be another reason for the basic diameter 36 in the '18 version other than solving the location issue from '09 though. If diameter 36 didn't become basic, they would have another problem with basic dimension 22 and the true profile being well defined. Would you agree?

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Yes, I would agree with that.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)

Quote (pmarc)

Yes, I would agree with that.
So a follow up question can be:
If this was a real part and the design department decided to make an update - keep size limits of 35.5-36.5 but also provide a 0.1 position tolerance at MMC, the 2018 version figure would become too stringent (I say that the general tolerance effectively provides zero location error when the AME size of the feature is 36.5). They would probably want to change the diameter to direct tolerance, add the position at MMC requirement, but keep everything else the same. Then they should notice the fact that dimension 22 basic is no longer meaningful (as the intersection it defines misses basic radial location). Would you then recommend changing 22 basic to direct tolerance (despite being a non-size dimension)?

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

I would then change basic 22 to basic 22.x to locate a gage plane on the cone and then apply a basic diameter at that gage plane.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

pmarc,

Seems very strange to recommend a gage plane on the cone for a chamfer (with its applicable complications such as basic diameter at that gage plane).
I know this is only an academic exercise, but still…..
I am just thinking (from an end user perspective) if I see a chamfer defined with basic angle, basic diameter and basic distance from a datum (granted very robust definition) …well I will just cringe.

But, to your credit, Burunduk asked a theoretical question …and he got a theoretical answer.
Just saying….

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

greenimi,
I am just providing answers to Burunduk's questions within the defined "boundary conditions".

Whether they are academic questions or not is a subjective thing because I might as well ask where, in your opinion, is a border between chamfer and regular cone. Do you know?

Just saying winky smile

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
greenimi, pmarc,
The question may be theoretical, but the dilemma on how to tolerance this kind of features is very real, and one that I face often. I generally hold the opinion that if a feature is non-critical, it should be reflected by a loose tolerance, not a loosely-defined tolerance. On the other hand, to echo greenimi, I don't want the manufacturer to "cringe".
So in case the suggestion about the gage plane was "academic"/"theoretical" would a practical one be different?

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Burunduk,
I wholeheartedly agree with this approach: "if a feature is non-critical, it should be reflected by a loose tolerance, not a loosely-defined tolerance". Unfortunately, in real-life situations compromises often have to made for different reasons. One of them is cringing manufacturing.

I think the solution that I see most often in similar situations is the 22 dimension directly toleranced and the directly toleranced angle for the slope. Even though both dimensions do not have standard intepretation in Y14.5, that's usually too weak argument to succesfully convince most people to change the scheme to basic dimensions and profile.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)

Quote (pmarc)

Even though both dimensions do not have standard intepretation in Y14.5, that's usually too weak argument to succesfully convince most people to change the scheme to basic dimensions and profile.

Unfortunately so.
Maybe with the industries moving to model based definition or minimally dimensioned drawings with a basic model, where not every basic dimension has to be graphically stated, it will become easier to stick with robust definitions without causing anyone to cringe.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

2
I agree that MBD should help, but only if organizations start to see value in seamless downstream consumption of the definition. I have seen quite many so called "MBD definitions" where not even 10% of the callouts would be consumable by a CMM, or tolerance analysis software. And it was not the fault of the CMM or the tolerance analysis software, but of the poorly prepared definition, full of directly toleranced non-size dimensions, directly toleranced angles, missing associated objects in the CAD model, etc., prepared to simply mimic "the good old fashioned 2D definition that has worked for 30-40 years, therefore not requiring any improvements".

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
pmarc,
Very well said. I wish ASME Y14.41 didn't support directly toleranced angles. Do you think they will ever be gone?

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Quote (pmarc)

I agree that MBD should help, but only if organizations start to see value in seamless downstream consumption of the definition. I have seen quite many so called "MBD definitions" where not even 10% of the callouts would be consumable by a CMM, or tolerance analysis software. And it was not the fault of the CMM or the tolerance analysis software, but of the poorly prepared definition, full of directly toleranced non-size dimensions, directly toleranced angles, missing associated objects in the CAD model, etc., prepared to simply mimic "the good old fashioned 2D definition that has worked for 30-40 years, therefore not requiring any improvements".

There are a couple of impediments for the MBD journey. One that comes in my mind is: how do the MBD practitioners know which annotation is machine-readeable and which annotation is only human readeable. The same way which dimension/ or annotation is CMM readeable (or QIF) or which one needs humans to interviene. Or at least that is my problem which I am not sure how to solve.

Another issue is unclear and very muddy definition of the UOS. ISO GPS did a very good job in ISO22081, but on the ASME side we have to do some "nasty adjustments". At this point, I am not sure when the general profile is applicable and when is not, in order to be sementically associated with the feature.

pmarc,
Do you have experience in this area of experise?




RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Quote (Burunduk)

I wish ASME Y14.41 didn't support directly toleranced angles. Do you think they will ever be gone?

Burunduk -- I really don't know. I assume (but that's just assumption) that in case of directly toleranced angles and a few other commonly accepted applications of directly toleranced dimensions that are mentioned in Section 10 of Y14.41-2019, they won't step ahead of 14.5. Although they probably should, because their input from the view point of automated downstream digital consumption of the definition could be truly beneficial, just like in case of the (U) modifier that had been first introduced to Y14.41-2003 before Y14.5 implemented it in 2009.


Quote (greenimi)

There are a couple of impediments for the MBD journey. One that comes in my mind is: how do the MBD practitioners know which annotation is machine-readeable and which annotation is only human readeable. The same way which dimension/ or annotation is CMM readeable (or QIF) or which one needs humans to interviene. Or at least that is my problem which I am not sure how to solve.

Another issue is unclear and very muddy definition of the UOS. ISO GPS did a very good job in ISO22081, but on the ASME side we have to do some "nasty adjustments". At this point, I am not sure when the general profile is applicable and when is not, in order to be sementically associated with the feature.

pmarc,
Do you have experience in this area of experise?

greenimi -- Regarding readability, I like to think about it this way. Machines (CMM's, CNC's, tolerance analysis software, etc.) are programmed by humans that use (or at least should use) standards like Y14.5, Y14.5.1 or Y14.41 to know how to do correct programming. If the standards do not provide clear interpretation for a tolerancing tool, the humans will not know what to do and the machines will not be able to read that.

As for the UOS issue, I agree that ISO did it quite wisely and that in ASME there is still some work to do. I do believe, however, that in MBD this problem can be mitigated to some extent by associating appropriate features of the model with the UOS callout in the CAD software used to prepare the definition. In other words, those features that have not been associated with the UOS callout in the CAD model are simply not controlled by it. Of course, this may work only if the organization and their business partners (customers, suppliers) have tools to be able to query the definition for the associated features.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

In a previous position creating full MBD models, one of the primary rules was that ALL features that didn't have a specific tolerance or FCF associated had to be associated to the default FCF. Every surface of the model had to be associated to a tolerance of some sort.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Quote (Ewh)

In a previous position creating full MBD models, one of the primary rules was that ALL features that didn't have a specific tolerance or FCF associated had to be associated to the default FCF. Every surface of the model had to be associated to a tolerance of some sort.

So if, for example, the designer "forgot" or missed the circular runout in Burunduk's first picture (from 2018 standard) for the 20.00-20.13 inside diameter feature or for 31.6-31.8 outside diameter feature, would you still associate this feature with the general profile?

Per the statement in the above quote, the features ( those two exemplifying above) did not have FCF associated.
Then what to do? How to read the MBD model?

Pmarc (since I do know your level of expertise and experience), how would you recommend to solve this issue? (Although very often encountered on the drawing level)

Many thanks

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)

Quote (greenimi)

So if, for example, the designer "forgot" or missed the circular runout in Burunduk's first picture (from 2018 standard) for the 20.00-20.13 inside diameter feature or for 31.6-31.8 outside diameter feature, would you still associate this feature with the general profile?

Greenimi, the features you mentioned are specified with a direct size tolerance. In this case, the model value can not be considered basic. If there is no basic shaft diameter, there is no unambiguous true profile and the general profile tolerance doesn't work.
If someone "forgot" to specify runout or position tolerances for those directly toleranced diameters, they should be contacted and told there's a location control missing.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Burunduk,
Based on your latest replay, you would consider the MBD incomplete, correct?

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
Yes, it would be incomplete.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

greeinimi,

A full MBD definition means that all features of the model have all necessary tolerances applied and that the tolerances have been associated correctly with the features. So if a surface of the model, like the diameter 20.00-20.13, has only the size requirement associated with it, then that surface is not controlled for orientation and location at all, despite that the general profile tolerance has also been used. Moreover, even with the runout tolerance specified, the surface may still not be fully defined in MBD sense because someone might forgot to correctly associate the runout tolerance with the surface in the CAD model - this of course will be interpretable by humans, but the machines will have no way to know that the runout tolerance applies to this particular surface.

Technically speaking, the UOS term is redundant (or maybe I should say auxiliary) in the full MBD approach, because querying the requirement specified at the UOS basis should give a reader necessary information as to which features of the model are controlled by it, therefore there is no need to say that the requirement is UOS.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)

Quote (pmarc)


Technically speaking, the UOS term is redundant (or maybe I should say auxiliary) in the full MBD approach, because querying the requirement specified at the UOS basis should give a reader necessary information as to which features of the model are controlled by it, therefore there is no need to say that the requirement is UOS.

I second that. There isn't really a need for a UOS tolerance in MBD. One can simply specify a loose profile tolerance to the appropriate group of surfaces (with the associativity as required by Y14.41 of course). UOS makes sense with minimally dimensioned drawing method when the model is not fully annotated.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Quote (pmarc)

Technically speaking, the UOS term is redundant (or maybe I should say auxiliary) in the full MBD approach, because querying the requirement specified at the UOS basis should give a reader necessary information as to which features of the model are controlled by it, therefore there is no need to say that the requirement is UOS.

Pmarc and Burunduk,
Should I understand that you ARE saying that you agree with a note such as "ALL UNTOLERANCED SURFACES OR FEATURES: PROFILE|XXX|DRF| as long as the wording "UOS" (Unless Otherwsie Specified) is NOT used.
Did I understand you correctly?
I am wondering about this group of words (UOS) and what could be so special about them and why "they" are so dangerous.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

greenimi,

What makes you think that I would agree with the note you proposed? There should never be such thing like UNTOLERANCED SURFACES OR FEATURES. Each feature should have a tolerance.

The point I was trying to make is that in MBD one can theoretically replace the UOS profile callout with just a profile callout and upon querying the callout, it will become clear which features it applies to.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
greenimi, I suppose that with "UNTOLERANCED SURFACES OR FEATURES" you try to borrow from the old-fashioned general tolerance wording "UNTOLERANCED DIMENSIONS..." but really there should be no untoleranced features, as pmarc noted. The idea is that a proper MBD model should include associativity between the tolerance, the considered features, and the datum reference frame (where applicable), for every requirement. In that sense, the "general" profile tolerance defined on the model should not behave differently than any other feature control frame on the same model (even if it lacks a leader directed to any model surface). Hence words like "UNLESS OTHERWISE SPECIFIED" don't say anything relevant (for MBD).

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Quote (Burunduk)

I suppose that with "UNTOLERANCED SURFACES OR FEATURES" you try to borrow from the old-fashioned general tolerance wording "UNTOLERANCED DIMENSIONS..." but really there should be no untoleranced features, as pmarc noted.
You are correct.
I am trying to convert everything I see on the drawing to the model. And since general profile is shown on the drawing then, consequently, I think the UOS should be included in the mix. However, looks like you guys disagree.
Do you think, the scope of general profile and the UOS note is achieved if the model is left incomplete?

By the way, what is the main scope of the UOS note: to reduce the drafting annotations (keep the drawing less crowded) or to complete (granted artificially) the feature's definition of the part?
Or maybe is neither one?

What is your opinion?

There are people, seen opinions on different forums, that the scope of UOS note is to make the drawing complete.
(Something like the major benefit that general geometrical tolerance is to make the drawing complete, instead, to potentially leave any tolerance open for users to define). What do you guys think?

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
greenimi, let's start by this:
If the product definition follows the rules and the supported practices, whether it is drawing based or model based, there may be untoleranced dimensions (basic or reference), but not untoleranced features.

Now, with that in mind, I think the answer to your question about the UOS note (or the general profile tolerance) is that its scope is primarily to complete the definition of the geometrical variation limits for the non-critical features of the part. BTW,Why "artificially:?

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Quote (Burunduk)

BTW,Why "artificially:?

Because you rely on a note (general note) and not on a well thought and functional need to fully define your part.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

(OP)
greenimi, just because it's a general note, doesn't mean that its use shouldn't be "well thought and functional". Deciding which are the more functionally important features that get unique tolerances defined for them and which are the less critical features that can be controlled by the general note takes some consideration and forming of a clear design intent. Assigning the appropriate profile tolerance value also requires consideration.

RE: Fig. 6-30 in ASME Y14.5-2018 - basic location of a thread start?

Well said, Burunduk.

I would just like to add that although it is common practice to specify general profile tolerance with the value that is the most generous of all tolerance values used on the definition (i.e., for the least important features from product function point of view), this is not a requirement.

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