Control location of a feature-set separately from form of the feature-set?

[cbrf23]

Is there an acceptable practice to control runout (axial location) of a feature-set separately from the form of the feature-set (which is controlled on another print)?



On this print, essentially, what I want to convey is:

THE FORM OF ALL FEATURES FROM POINT X TO POINT Y IS CONTROLLED BY PRINT 109-2367​

THE LOCATION OF ALL FEATURES FROM POINT X TO POINT Y IS CONTROLLED BY THE RUNOUT TOLERANCE ON THIS PRINT​

Here's what I came up with - I just wanted to get some feedback on whether or not the intent is clear, and if you think this is an acceptable depiction of the requirements as described.
*Our drafting standard for the most part adheres to ASME requirements - Y14.5M-2009, Y14.100 (*our flags are special...), etc.

The background:
I have two prints: a machined part print, and a print which describes a modular feature-set used on the machined part.
This common feature-set (colloquially known as "the profile") is used on multiple parts.
Since each profile feature-set may be used on 1,000's of prints, we keep all dimensions relating to the profiles on their own prints for purposes of maintenance and consistency.

The profile print itself controls the form of the profile feature-set (profile of a surface tolerance of .002").
This is inspected using a contour tracer, which historically has worked very well and I'm told is within an acceptable limit for capability.

The profile has a tight tolerance because it has to fit with a mating part, however the location of the profile feature-set is determined ad-hoc for each application.
For this application, we want to control the runout of the profile in relation to another feature of the part. The entire profile can be allowed to runout by up to .020" and the assembly will function as intended.

 

[Belanger]

That spherical-type part seems confusing; At first glance I would say the plus/minus tol of 0.2 is in conflict with the basic dim on the sphere.
The general rule as I see it would be that when applying a profile tolerance, any dim that defines the shape of the feature must be locked as a basic dim for the profile to make sense. (A dim that ties that feature to a datum reference doesn't have to be basic.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[greenimi]

I believe changing the datum feature reference in the lower segment from B to A would actually make the "delta" modifier meaningless

Pylfrm,

As is currently shown –now-- on the draft (Nov 2015), in my opinion, is incorrect because it is a composite callout (not single segments callout) so,
- either A is added as primary (and keep also B secondary),
- either replace B with A (as primary)
- either have no datum feature shown on the FRTZF
in order to follow the rules of the composite callout.
As far as explaining the differences between “delta” versus the ”non-delta”on Fig 11-20 (same draft) I would like someone with more knowledge than me to try to explain it in the layman terms what those differences would be. I am afraid that I will just muddy the waters, if I will try to do it myself with no gain for anyone.

 

[pmarc]

Since there are no datum feature references, what's to stop me from simply shifting the surface axially relative to the upper segment tolerance zone until it falls in? Doesn't the tolerance zone extend to cover the entire actual feature, even if the extent of that feature differs substantially from nominal?

What's to stop you from doing this? Other than - if you did that it would mean the composite callout (with or without dynamic zone modifier), and actually any other single segment profile callout applied to a cone (like in Figs. 4-3 or 4-44 in Y14.5-2009), would never be able to control size of that cone - I guess nothing.

 

[greenimi]

pmarc,

May I ask you, why do you think that 11-20 in the draft, in the left picture the PLTZF profile is shown as 0.2 A primary and B secondary but in the right picture named "or this on the model" the PLTZF is shown as 0.02 (assuming you are ignoring the FRTZF missing callout). Basically I am asking why 0.2 versus 0.02 on the locating pattern TZF?

This picture looks like a mess in my opinion.

 

[pmarc]

Yes. The figure indeed looks like a mess. It is one of the reasons (main) why I said it needed to be improved. Notice that this is rev. C of the figure. I am wondering how did revs. A and B look like, if the committee considered rev. C as an improvement.

 

[greenimi]

Okay. I understood.

Let’s pretend for a moment that the composite callout on fig 11-20 has datum feature A shown as a primary for the lower segment FRTZF ( instead of datum feature B).

I still would like to go back to my original question: what would be the differences (if any) between FTTZF with “delta” versus the same composite callout with “no-delta”

Could anyone clarify what would be the dynamic TZ effect and how to practically use it?

Thank you

 

[pylfrm]

if you did that it would mean the composite callout (with or without dynamic zone modifier), and actually any other single segment profile callout applied to a cone (like in Figs. 4-3 or 4-44 in Y14.5-2009), would never be able to control size of that cone

I don't think the profile tolerances in the figures you mention can control "size" either, at least not by themselves. In combination with other tolerances not shown though? Sure.

Please see the attached image. I would expect the diameter of the cone at the large end could be anywhere between 370 + 150 + 0.2 * sqrt(2) = 520.28 (at maximum material condition of both profile tolerances) and 370 - 150 - 0.2 * sqrt(2) = 219.72 (at least material condition of both profile tolerances). Would you agree?


pylfrm

 

[pmarc]

pylfrm,
Yes, I would agree with the numbers. Profile tolerance in axial direction definitely has influence on size of the diameter of the cone at the large end. So if we are going to apply axial profile of approx. 228 to the large end of the cone in fig. 11-19 from the draft, then yes, the large end may have an actual diameter of 60

But let's imagine we applied much smaller axial profile callout, say 0.1. Do you still not see how it would be possible to meet the lower segment requirement with the delta modifier but not the upper? If so, is it because in your opinion the tolerance zone defined by the lower segment is able to shift in axial direction relative to the tolerance zone defined by the upper segment?

 

[pylfrm]

pmarc,

I'll try to answer your first question for two scenarios. In both cases, I'll answer based on a sample part that has an actual diameter of 60 at the large end, but is otherwise perfect basic geometry.

--------

Secnario 1:
The additional tolerance (0.1 profile) applied to the large end face has no datum feature references, and applies as a simultaneous requirement with the upper segment tolerance (0.2 profile). The lower segment tolerance (0.02 dynamic profile) is a separate requirement.

In this case, I'd say that the sample part would meet the lower segment requirement, but cannot meet the simultaneous requirement of the other two tolerances. I don't think you can narrow down the failure any further than that.

--------

Scenario 2: The additional tolerance (0.1 profile) applied to the large end face references the conical surface as primary datum feature.

In this case, I'd say the sample part meets both the upper segment tolerance (0.2 profile) and the lower segment tolerance (0.02 dynamic profile), but fails the additional tolerance (0.1 profile) by a large margin (approx. 227.9 based on your number above).

========

I don't believe my answers above rely on the lower segment tolerance zone shifting axially relative to the upper segment tolerance zone.

I do believe that such shifting is allowed though, by two different mechanisms in this case. First, by the usual rules of composite profile (no translational constraint for lower segments). Second, by the equivalence between a shift of X axially and a shift of X * sin(15° / 2) normal to the profile (as allowed by the dynamic tolerancing modifier).

Thoughts?


pylfrm

 

[pmarc]

pylfrm,

First, my apologies for late response. I was really busy during last 2-3 days and simply could not find enough time to sit down and write a reply.

Second, with regard to proposed scenarios...

Scenario 1:
I do not see a reason to disagree with your interpretation. Also, looks like you agree that there is a way to meet the lower segment of the composite profile callout (with dynamic zone modifier), but not the upper segment, don't you?

Scenario 2:
While I agree that: "a sample part that has an actual diameter of 60 at the large end, but is otherwise perfect basic geometry meets both the upper segment tolerance (0.2 profile) and the lower segment tolerance (0.02 dynamic profile), but fails the additional tolerance (0.1 profile) by a large margin", I do not think the sample part is ever allowed to have an actual diameter of 60 at the large end. It is because the composite profile callout and the additional profile tolerance of 0.1 must both be met to have the actual cone produced according to the print, regardless of whether the callouts consitute simultaneous requirement or not. In other words, in order to meet the additional profile requirement of 0.1 wrt A, the large end of the cone can't be anywhere else except within the two-parallel-planes tolerance zone which center is located at basic distance of ~113.9 from the apex of the theoretical perfect cone (theoretical datum feature A simulator). To make it possible, the actual diameter of the large end of the cone must be of ~30 in first place.

Third, because I am not sure if the underlined part of your statement from July 2nd: [/]"I have my doubts about Fig 11-19 from the draft though. I don't see how it would be possible to meet the lower segment requirement but not the upper, and I don't see that the dynamic tolerancing modifier has any effect in this case."[/i] has been answered, do you now see the effect of the dynamic zone modifier or not really?

 

[pylfrm]

pmarc,

No worries about the delay. I appreciate the time you're taking to discuss this. Anyway, it's been 2 weeks already, so what's another few days?

Scenario 1:
I don't think you can specifically say that the upper segment is failed in this case because it is now just one component of a single (simultaneous) requirement. The sample part could be moved around such that it falls within the upper segment tolerance zone, the additional flat tolerance zone, or neither, but not both at the same time. So I guess I still disagree, but only on a nitpicky semantic level that's probably not worth worrying about. I think we're in agreement on the important part here.

Scenario 2:

In other words, in order to meet the additional profile requirement of 0.1 wrt A, the large end of the cone can't be anywhere else except within the two-parallel-planes tolerance zone which center is located at basic distance of ~113.9 from the apex of the theoretical perfect cone (theoretical datum feature A simulator). To make it possible, the actual diameter of the large end of the cone must be of ~30 in first place.

I agree completely.

do you now see the effect of the dynamic zone modifier or not really?

Still not really in this case.

Because it is established by a lower segment of a composite FCF, the 0.02 tolerance zone is free to translate relative to the 0.2 tolerance zone of the upper segment. Agreed?

As mentioned at the end of my previous post, I think a relative axial shift can accomplish the same thing as a shift normal to the profile, so the dynamic tolerancing modifier doesn't allow anything that is not already allowed in another way. Thoughts?


pylfrm

 

[axym]

Hi All,

This looks like a very interesting thread. I am quite interested in people's opinions on dynamic profile and the combination of directly toleranced dimensions and profile - it's nice that there are other people who care about these things. I will read through the posts over the next day or so and see if I have anything to add.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[axym]

Hi All,

Here are some thoughts.

First, I applaud both pylfrm and pmarc for being able to discuss this in such fine detail. These examples are very difficult, because of several subtle complicating effects occurring at the same time.

I will try to briefly explain my understanding of the effect of the dynamic profile (delta) modifier. It allows the profile zone to "grow" and "shrink", so that it does not control the size of the feature. In mathematical/geometric language, it allows the profile zone to freely "offset" or "progress". I would say that the best illustration of dynamic profile in the new draft is Fig. 11-37, because it is relatively free of complicating effects. You can see that the dynamic profile zone is oriented and located relative to the datum features, but is allowed to progress (grow and shrink while maintaining the same thickness) in order to adapt to the as-produced "size" of the feature.

I would say that the effect of dynamic profile is much more difficult to see in the figures with the conical considered feature. As pylfrm has pointed out, there are other transformations that would achieve the same overall result. One of them is the conical geometry, which has the special-case property of axisl translation having the same effect as radial expansion/contraction. The other is the dynamic profile modifier being in the lower segment of a composite FCF, which allows the tolerance zone to freely translate.

The axial translation effect with the cone also brings up some deep issues relating to tolerance zone extent. Here's a question. Let's say that I manufacture a perfect conical surface whose smaller diameter is 30, length is 40, and larger diameter is 40.5322 (i.e. the included angle is exactly 15 degrees). Would it pass the 0.2 profile tolerance requrement in Fig. 11-19? How about the 0.02 dynamic profile?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[pmarc]

Evan, pylfrm,

There is no doubt that things are more complicated because the considered features are conical.

I think the key part of the problem is exactly the tolerance zone extent issue. Where exaclty in axial direcion is the start and the end of the tolerance zones? Do the tolerance zones have infinite length or maybe the lengths are limited by other tolerances? If they are limited, can they be different for different segments of composite profile callouts?

In one of my first posts in this thread I said:

In fig. 11-19, I do not see anything wrong in the callout itself. If we imagine that both conical tolerance zones have certain axial length identical for both segments (or in other words, that the smaller tolerance zone does not/cannot move axially relative to the larger tolerance zone), the lower segment of the profile callout (with the triangle symbol) is solely a form control - the 0.02 tolerance zone is free to expand or contract within the 0.2 tolerance zone. If the lower segment did not have the triangle symbol, the callout would make no sense, because the requirement from the lower segment would always override the upper segment.

You may ask, why should we imagine/assume this at all? I think it is because in absence of any datum feature reference that would constrain upper segment TZ relative to a datum or datums, any possible movement of lower segment TZ within the upper segment TZ does not really matter, because the upper segment TZ is also free to shift and can always be brought back to stay perfectly "centered" (axially and radially) on the lower segment TZ. So as a matter of fact, the only "movement" the lower segment TZ has relative to the upper segment TZ is its ability to shrink and grow. And this is what the dynamic profile modifier does in fig. 11-19. Like I said before, in my opinion, if the lower segment did not have the triangle symbol, the callout would make no sense, because the requirement from the lower segment would always override the upper segment. Does it make sense what I am saying?

With regard to fig. 11-20, I believe we would not have any discussion if "only" the composite FCF was changed to two single segment callouts: |prof|0.2|A|B| and |prof||0.02 [Δ]|A|B| (similar to what has been done in fig. 11-38). Or would we?

 

[AndrewTT]

I did not read every line of this thread so forgive me if this has already been addressed or if this is super obvious.

If you end up using profile to control the surface of revolution then I believe you need to use profile of a line and not profile of a surface. I would also recommend calling out how many instances of measurement are required for your profile of a line requirement (e.g., every 10°).

 

[greenimi]

If you end up using profile to control the surface of revolution then I believe you need to use profile of a line and not profile of a surface.

I don't know if I would agree with you.
Are you saying that the profile on a cone is not a functional requirement? Never?

I would also recommend calling out how many instances of measurement are required for your profile of a line requirement (e.g., every 10°).

I would also stay away from defining the design intent based on a chosen inspection method and I would not specify on the product drawing in how many instances this surface to be measured. This is exactly the same thing to specify that a straight cylindrical pin is to be measured in 10 places or .010 measurements apart or something like that. It is a risk management to define in how many places the part to be measured.

 

[AndrewTT]

Lets highjack this tread for a bit and discuss profile of a line vs. profile of a surface. When to use POL is a question that has come up at my work a few times b/c no one really understands it here. I could totally be wrong but my understanding is if you use POS then the entire surface of revolution must be checked. If you use POL then you check individual line segments. How many line segments do you need to check? I believe that it is up to the inspector unless there is written instructions (on the drawing or some other controlling document).

Yes, I would say absolutely design the part based upon its intent but the part also has to be made and inspected.

I would appreciate any input from someone who has an opinion/knowledge on POL vs. POS.

Thanks.

 

[greenimi]

Please, do not hijack this thread. It is quite interesting to learn about dynamic tolerance zone.

Could you, please, start a new thread about profile surface versus profile of a line and their respective measurements issues.

 

[greenimi]

AndrewTT,

I did it for you. Please provide more info in the applicable thread

 

[greenimi]

After unsuccessful attempt to "steal" this thread I would ask you guys where we are?

Please, Please, do not let his thread to die as is quite interesting to learn and specially to understand new stuff.
- Composite on 11-20 draft with and without dynamic TZ
- Also pmarc dropped in the mix two single segment callout ( and I will add " with and without dynamic delta TZ" just for fun)