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.

 

[CheckerHater]

I suggest you explain your intent on the face of the drawing in form of a verbal note, exactly the way you explained it to us:

"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"

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[pmarc]

cbrf23,
The approach you described makes sense, however...:
1. The profile of a surface tolerance of .002 specified on the profile print does not only control form, but also size of the profile, thus you may want to modify first part of your note accordingly.
2. I assume the print you showed us is intentionally incomplete, and that there is something on that print that controls location of the profile along the axis of the feature. If not, I think you may want to consider use of profile tolerance instead of circular runout, as the circular runout does not locate the profile axially.

 

[pylfrm]

cbrf23,

To clarify, is "the profile" (X <--> Y) a surface of revolution? You're using a circular runout tolerance, but your drawing doesn't have diameter symbols on the 3.500 or 2.375 dimensions.

Could you show us "PRINT 109-2367", or at least the relevant portions of it? The actual dimension and tolerance values aren't important, but the general scheme and the notes might be.


pylfrm

 

[Belanger]

pmarc -- Like you, I believe profile controls size, but unfortunately that was debated here a while ago and the conclusion seemed to be that it doesn't have to. (Imagine a cylindricity tolerance replaced with profile of a surface, while keeping the size as a ± tol. I say no but others seem to think that's OK.)

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

 

[cbrf23]

Hi all,

I greatly appreciate the input. I like the idea of supplementing the depiction with the notes, so I will add that.

To answer some questions:
The example shown is just a representation to describe the situation, not the actual drawing I'm working with - the actual drawing, and the profile, are proprietary designs that I cannot share. The profile drawings have all the basic dimensions and a profile tolerance from x to y - that's about it.

Yes, from x to y (the profile) is a surface of revolution. Missing diameter symbols are a result of a hasty draft to serve as analog for the real print (see answer above)

Yes the profile is intended to control both form and size.


As far as profile being used to control form independent of size, I think ASME Y14.5 (2009) is pretty clear that it can be used that way.
For example, in 8.2 the distinction between controlling form and controlling a combination of form, size, orientation, location is clearly made:

In 8.4.2, again a very clear distinction is made between the use of profile to control form independently, or to control a combination of form, size, etc.

And then we have clear examples showing profile controlling form, with size controlled through a ± tolerance:

And profile controlling both form and size together:

 

[pmarc]

J-P,
Well, if the diameter of the "profile" on the profile print is dimensioned with +/- tolerance, or there is no diameter dimension and a "radial" height of the profile height is given as basic dimension (could you confirm, cbrf23?), then I say the profile of surface tolerance controls form only :-(

If the diameter is basic, the profile of a surface tolerance controls size and form.

I am still missing one more answer from cbrf23. What controls location of the profile between points x and y on the print of the entire part?

 

[pylfrm]

cbrf23,

If the profile is fully defined with basic dimensions (including diameter) on the profile print, then to control its axial location you could replace the circular runout tolerance with profile of a surface. You would need to change the datum feature references to include an appropriate feature, and add a basic dimension from the profile to that feature. Your flag note could read "SEE PRINT 109-2367 FOR BASIC DIMENSIONS AND ADDITIONAL TOLERANCES" or similar. I don't think the note would need to explain the goal of each print; the tolerances should speak for themselves.


While it is true that the profile tolerance in ASME Y14.5-2009 Fig. 8-17 does not control size, that is only because there is no such thing as size for a conical surface in isolation. A cone is fully defined by included angle alone. Size is only meaningful for a cone in relation to something else. The profile tolerance has no datum feature references, so that is not the case here.


pmarc,

For a complex shape like the one in question, I'm not sure there's a meaningful or well-defined distinction between "form" and "size". Do you mean that the lack of a basic diameter dimension would allow the profile of a surface tolerance zone to uniformly expand or contract radially?


pylfrm

 

[pmarc]

pylfrm,
Yes, that is basically what I mean.

Even if that is not the case here, it is possible to imagine that the profile print fully defines FORM the contour between points X and Y by giving all necessary basic dimensions on one side of the axis only. In that case additional +/- diameter dimension will be nothing but a separate SIZE control, and, like you said, the profile of a surface tolerance zone will be allowed to uniformly expand or contract radially.

This concept has been covered/clarified in the draft of new Y14.5? Figures 8-17 and 8-18 from 2009 version have been modified and now they do not have +/- diameter dimensions at all. Basic diameters have been used instead, extra profile callouts replacing +/-0.2 size tolerances have been added, and the 0.02 profile callouts have been changed to dynamic profile tolerances - callouts that define tolerance zones that are allowed to uniformly expand or contract radially within the larger profile tolerance zones. These new figures in the draft still need to be improved, but their intent is quite clear, at least in my opinion.

 

[pylfrm]

pmarc,

Understood. I can indeed imagine the concept, but I'm still not convinced it's kosher. The main sticking point for me is the following:

Profile tolerances are used to define a tolerance zone to control form or combinations of size, form, orientation, and location of a feature(s) relative to a true profile.

A true profile is a profile defined by basic radii, basic angular dimensions, basic coordinate dimensions, basic size dimensions, undimensioned drawings, formulas, or mathematical data, including design models.

For what (little) it's worth, the second sentence of para. 11.10 of the 24 November 2015 draft supports that the true profile must be fully defined by basic dimensions.

I've never had a problem with Figs. 8-17 or 8-18 because the profile-toleranced surface is fully defined by the basic angle in both cases. The toleranced dimensions are only involved in defining the relationship between the toleranced surface and some other feature.

Fig. 11-20 from the draft seems fine to me, although I wonder if the datum feature reference for the lower segment was supposed to be A instead of B based on the "Means this" explanation.

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.


pylfrm

 

[Belanger]

pylfrm,

The sticking point with Figs. 8-17 and 8-18 was that the toleranced dims were defining the very contour of the feature being toleranced by profile of a surface. Thus, it was not a "true profile." When the standard mentioned that a profile zone may be a refinement of a toleranced dimension, they meant a refinement of a location (such as in Fig. 8-27). Unfortunately, they didn't make that distinction, although maybe it's in the new draft.

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

 

[pylfrm]

Belanger,

I disagree. All cones with the same basic included angle have the same contour. Changing the diameter at a gage line or an intersection with a flat surface effectively shifts the cone axially, but does not change the contour itself.

For that reason, I think Fig. 8-18 is just another example of location refinement like Fig. 8-27 shows. This would be more obvious with a basic diameter dimension and a toleranced axial dimension, but I don't think it actually matters which is which. The dimensions only have meaning as a pair.


pylfrm

 

[Belanger]

It all comes down to what we mean by the term "true profile." Is a circle that's given a diameter tolerance a "true profile"? I would say no.

To me, Fig. 8-17 is OK (using the Ø30 ± 0.2) only because it has no datum to locate that zone. So the profile zone can move left/right and of course the diameter then changes, depending on where the zone is superimposed, simply because it's an angle. But Fig. 8-18 seems to have been the problem (in my estimation, at least). That's because of datum B, which locks the profile tolerance zone at a precise left/right location. By doing that, the Ø24 should have been basic.

Here's another approach to the topic -- see the attached graphic. Would you say that the first picture is acceptable per Y14.5? (The one that's a partial arc.)
What about the second picture? (The one that's a full circle.)

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

 

[pmarc]

pylfrm,
I see what you are saying and agree that most people may find my idea illegal. I personally think that the approach I tried to describe falls under "reasonable extension of principles" category, because as of today there is no other way (apart from a tricky note) to separate radial size of a surface of revolution from its longitudinal form than use of a profile tolerance (and for that purpose the true profile in axial direction has to be fully defined with basic dimensions) in combination with a directly toleranced diameter.

With regard to your comments about figs. 11-19 and 11-20 from the draft:
- Yes, in fig. 11-20 I also think there should be A, not B, referenced in the lower segment of the composite profile callout;
- 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.

For those who are interested to see both mentioned figures from the draft, they are here:

http://files.engineering.com/getfil...1e9-4f69-b717-a7586f1ba5c8&file=fig.11-19.PNG

http://files.engineering.com/getfil...f15-4d26-bcff-9829f7631c85&file=fig.11-20.PNG

My apologies for their poor quality and some traces of my markups, but like I said before, these figures, in my opinion, still need to be improved (for example I do not understand why both "Means this" pictures have 29.8 and 30.2 limits drawn perpendicular to the cone axis).

 

[pylfrm]

Belanger,

I'd say the picture with the partial arc (R42±0.5) and the picture with the full circle (diameter 84±1) are equally questionable because in both cases the true profile is not fully defined by basic dimensions.

For Fig. 8-18, would you say that the true profile of the conical surface itself (not in relation to anything else) is fully defined by basic dimension(s)? If not, what about a modified version with diameter 24 BASIC instead of diameter 24±0.2, and 18±0.72 instead of 18 BASIC for the axial dimension?


pmarc,

I don't want to say for sure that what you propose is illegal, just that I'm not convinced it's legal. You certainly have a point about the current lack of alternatives though. Personally, I'd probably go with the "tricky note" approach (perhaps specify the dimension as basic, but note that it can take any single value within some defined range), but I don't have a terribly strong opinion on the matter.

For the draft Fig. 11-19, could you describe a part would meet the lower segment requirement but not the upper? I still can't imagine one.


pylfrm

 

[pmarc]

For the draft Fig. 11-19, could you describe a part would meet the lower segment requirement but not the upper? I still can't imagine one.

Sure. Take a cone that has a form error (straightness, roundness and taper) within 0.02, but its actual diameter at the right end is for example 60, not 30. That feature will meet the lower segment requirement, but not the upper segment.

 

[Belanger]

pylfrm,
In Fig. 8-18, I would say that the cone is currently not defined as a true profile. Changing the diameter to a basic dim of 24 would make it a true profile.
As for changing the diameter to a basic 24 and then changing the axial dim of 18 to a plus/minus tolerance, I think that would still be a true profile. The diameter of the cone is what directly impacts the true profile, but the 18 is merely relating the cone to the datum, which is not required to be basic.

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

 

[pylfrm]

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?


Belanger,

Please see the attached image for another modified version of Fig. 8-18. Would you say that the spherical surface is a true profile fully defined by basic dimension(s)?


pylfrm

 

[greenimi]

Probably to understand better the dynamic TZ symbol worth to explain what would be the differences between 11-20 and 11-20 with no "delta". --of course datum feature A on both cases in FRTZF.

 

[pylfrm]

greenimi,

Now that I think about it again, I believe changing the datum feature reference in the lower segment from B to A would actually make the "delta" modifier meaningless. What to you think?


pylfrm