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.

 

[pylfrm]

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?

As you've probably guessed from my earlier posts in this thread, I'd say it would pass both tolerances.

Here's a related example that might be useful to consider:
Drawing specifies a short piece of tube with inside diameter 19.4678 BASIC, outside diameter 30 BASIC, and length 8 BASIC. A profile tolerance of 0.2 without datum feature references is applied to one of the flat end faces. Now imagine I manufacture a tube with inside diameter 30, outside diameter 40.5322, and length 8. Cylindricity, concentricity, flatness, perpendicularity, etc. are all perfect. Would it pass the profile tolerance?

Despite some superficial differences, I think thread1103-363314 was basically a discussion of the same issue. It seems to me the overwhelming consensus was that the extent of a surface is not controlled by a profile tolerance applied to that surface. While this may not be explicitly stated by the standard, I think any other answer will be pretty hard to justify.

If we imagine that both conical tolerance zones have certain axial length identical for both segments

How would you determine this length? Also, how would you determine where to place the tolerance zone ends relative to the part for inspection?

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|

Agreed. That would would also have the benefit of matching the description in the "Means this" section.

Also pmarc dropped in the mix two single segment callout ( and I will add " with and without dynamic delta TZ" just for fun)

I'd say |prof|0.02|A| would be equivalent to |prof|0.02 Δ|A|B| for the second single segment.

pylfrm

 

[pmarc]

How would you determine this length? Also, how would you determine where to place the tolerance zone ends relative to the part for inspection?

I was trying to say that it doesn't really matter in fig. 11-19. My point was that since the upper callout does not contain any datum feature references, the ability of the smaller tolerance zone to shift relative to the larger tolerance zone is actually taken away by the fact that the larger tolerance zone can always be aligned radially and axially with the smaller tolerance zone.

Here's a related example that might be useful to consider:
Drawing specifies a short piece of tube with inside diameter 19.4678 BASIC, outside diameter 30 BASIC, and length 8 BASIC. A profile tolerance of 0.2 without datum feature references is applied to one of the flat end faces. Now imagine I manufacture a tube with inside diameter 30, outside diameter 40.5322, and length 8. Cylindricity, concentricity, flatness, perpendicularity, etc. are all perfect. Would it pass the profile tolerance?

I say it would. But let's say that instead of datumless profile callout of 0.2, a perpendicularity tolerance of 0.2 is appplied to the end face of the tube relative to the datum axis derived from the outside diameter. I am interested to know the value of maximum possible as-produced angle between the end face and the datum axis (assuming the face was manufactured perfectly flat). Would the answer be the same for OD manufactured to 30 in case 1, and 40.5322 in case 2?

 

[pylfrm]

But let's say that instead of datumless profile callout of 0.2, a perpendicularity tolerance of 0.2 is appplied to the end face of the tube relative to the datum axis derived from the outside diameter. I am interested to know the value of maximum possible as-produced angle between the end face and the datum axis (assuming the face was manufactured perfectly flat). Would the answer be the same for OD manufactured to 30 in case 1, and 40.5322 in case 2?

Maximum possible angle increases as the outside diameter decreases. Because we haven't established a minimum outside diameter, I'd say the angle is unbounded.

For cases 1 and 2, I calculate 0.382° and 0.283° respectively.


pylfrm

 

[axym]

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?

I would describe this differently. But I would also repeat that this example is very difficult to sort out, because of the multiple sources of "movement".
-the lower segment TZ can freely translate relative to the upper segment TZ because it's a composite FCF. The dynamic profile modifier allows the lower segment TZ to shrink and grow (offset).
-if the lower segment did not have the triangle symbol, I agree that the callout would make no sense. The lower segment would be allowed to shift relative to the upper segment, but this would provide no advantage and the optimal shift would be zero.

The callout in Fig. 11-19 may not make sense anyway, depending on what conclusion we reach on the tolerance zone extent issue. See below.

pylfrm,

My question about the "oversize" cone, and your related question, brings the issue of tolerance zone extent to a head. If the answer to these questions is yes, then the tolerance zone can extend a large distance past the boundary of the basic surface. I had not thought it through and come to this conclusion before, and yes seems like an uncomfortable result, but I can't come up with an argument that it should be no. Does this mean that a profile zone can extend an indefinite distance past its basic surface? There must be more to it, or we could reach some absurd conclusions.

Back to Fig. 11-19. If the profile zone can be extended, then the zone can accommodate a 15 degree cone of any "size". This would mean that the upper segment 0.2 profile tolerance would only control the form of the cone and not the size. This would make the use of a composite FCF unnecessary, because the upper and lower segments would both be controlling form only. Does that make sense?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[pylfrm]

axym,

It has never seemed like an uncomfortable result to me. The alternatives, on the other hand, do.

Do you have an example of an absurd conclusion this would allow? I haven't thought of any, although that may be due to a differing opinion of what constitutes absurdity.

Regarding Fig. 11-19, that is pretty much how I see it -- two different segments controlling the same thing. That interpretation makes sense to me, and so the figure does not.


pylfrm