ASME Y14.5 2009 Section 7.53 Coaxial Pattern of Features of Size Question

[Zach Lankton]

Quick Question Regarding ASME Y14.5 2009 Section 7.53 Coaxial Pattern of Features of Size Question
Ref Fig 7-49 & Fig 7-51

Attached is a photo of the drawing section that I am looking for opinions on.

There are 4 different size holes that are coaxial.

Section 7.5.3.3 Excerpt:
"...Where holes are of different specified sizes and the same requirements apply to all holes, a single feature control symbol, supplemented by a notation such as TWO COAXIAL HOLES is used. See Fig. 7-51. The same tolerance zone relationships apply as for Fig. 7-49."

This is well covered by Sec 7.5.3.3 & Figure 7-51 in the standard where requirements are the same for each hole.

However, in my case the requirement for one of the holes is different.

The engineer chose to use 4 composite FCF's. The intent seems clear to me that the lower segment should control coaxiality of all 4 holes, with one hole needing to be held to a tighter tolerance zone.

Figure 7-49 shows a single composite tolerance zone. My interpretation has been that the axis of the tolerance zone is established the same but the tolerance zone at this hole location is smaller.

So my question is...
Does the current drawing make this intention clear or am I totally wrong? If so, is there a better way to annotate this intention?

Thanks in advance!
Zach

 

[3DDave]

I would use use the notation "SIM REQ A" on each of the lower segments of the four FCFs.

 

[Zach Lankton]

Thank you for your reply, is there in reference material on this you can point me to? I cant find anything in the standard on it.

 

[3DDave]

See 2009, 4.19.

 

[Zach Lankton]

Awesome! Thank you! So Just to clarify, is the letter "A" just a way of separating these from other composite FCF's elsewhere on the print where the upper segment datum references are the same? (A|B|C(M))?

 

[3DDave]

Yes. It is unfortunate that the committee does not think through the simple communications cases of 0, 1, and Many; mostly concentrating on "1". It's like a board game developer who doesn't consider what happens on round 2.

 

[Zach Lankton]

Haha! Yes! These cases are easy enough to describe with the simple prints used in the standard...
But the print in question here has 12 views, 14 cc's, 7 Datums, 21 Features All Simultaneously Controlled back to A|B|C(M), etc...

I've been working with this part for 6 years so I understand its function very well. But when new people come in these questions of interpretation pop up. Something that I understand implicitly now becomes a battle to explain. I find myself turning to the standard for backup and even that fails me sometimes. However, this print is not without its problems as seen in my post.

Thank you once again! I really appreciate your help!

 

[chez311]

So I might get some flak for this but I'm going to stick by my answer in your original post in the other standards forum (

https://www.eng-tips.com/viewthread.cfm?qid=444704)

- the addition of simultaneous requirements to a lower FCF/FRTZF in a composite tolerance is not clear as to what it actually accomplishes.

For support on this, I hope Evan doesn't mind me referencing his answer a few months back (in this thread towards the bottom

https://www.eng-tips.com/viewthread.cfm?qid=437957)

which cleared things up for me and I have referred back to ever since.

By default, FRTZF's are not subject to simultaneous requirements. To override this default, Y14.5 allows SIM REQT annotations to specified beside each FRTZF. But I don't think that the effect of SIM REQTS is completely straighforward in this case. Would SIM REQTS control the relative orientation and location of the two FRTZFs (so that the two zone patterns share a common center), or just control the relative orientation of the two FRTZFs (so that they don't share a common center) ? I would say that if you asked several Y14.5 experts, the results would not be unanimous.

What exactly are you gaining from utilizing composite tolerance anyway? The solution as I said before would be to change all the callouts as shown to Multiple Single Segment. I would also keep the notation "SIM REQ A" in the lower FCF as suggested by 3DDave as it is again not clear in the standard whether datumless FCF's are subject to a default simultaneous requirements, the addition of a note however makes it clear.

 

[axym]

Zach,

This is an interesting question, because it brings up some gray areas regarding patterns, composite FCF's, and simultaneous requirements.

If the intent of the lower segments is to control the mutual coaxiality of the 4 holes, I don't think composite FCF's will work.

Y14.5 does state in 4.19 that SIM REQT annotations can be placed next to each lower segment of the composite FCFs. But the exact effect of this is not described in detail - if you asked each Y14.5 committee member about this, I believe the opinions would be split. Some say that the SIM REQT annotations would combine the lower segment tolerance zones into a pattern, and thus control the mutual location (coaxiality) of the 4 holes. Others would say that only the mutual orientation of the holes would be controlled. I would agree with the second interpretation, and suggest single segment FCF's instead of composite FCF's if coaxiality is intended.

There is also a debate over whether not simultaneous requirements applies by default when there are multiple single segment FCF's with no datum features referenced. I would say that it does not, and explicit annotations would be needed if you want the coaxiality.

So on your drawing I would recommend two single segment FCF's for each of the 4 holes, with SIM REQT annotations next to each of the lower segments. Like this:

dia 9.011 9.025
|POS|dia 0.25(M)|A|B|C(M)|
|POS|dia 0.20(M)| SIM REQT #1

dia 7.81 7.85
|POS|dia 0.25(M)|A|B|C(M)|
|POS|dia 0.20(M)| SIM REQT #2

Similar for the 3rd and 4th holes.


Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[3DDave]

So SIM REQT doesn't mean what they say it means?

"In a simultaneous requirement there is no translation or rotation between the datum reference frames of the included geometric tolerances"

 

[chez311]

Hey Evan - speak of the devil! As I said I hope you don't mind me referencing you when I talk about composite tolerance and simultaneous requirements, it seems to be a topic that comes up fairly often and your reply really helped me understand some of the confusion and misunderstanding on the topic ever since.

As can be seen by my previously reply I clearly agree with you - especially in this case I think changing to Multiple Single Segment perfectly accomplishes the design intent, no need to confuse things with composite tolerance.

 

[chez311]

3DDave,

Its right there in the sentence you referenced:

"In a simultaneous requirement there is no translation or rotation between the datum reference frames of the included geometric tolerances"

Note - it says between the datum reference frames, NOT between the features. Per the definition of composite tolerance the lower FCF/FRTZF has cannot be constrained in translation to a DRF and is only constrained in rotation. So per the standard a feature or pattern would have to be constrained first in translation to a DRF to be held in translation/location simultaneous requirements to each other, and a FRTZF cannot be constrained in translation to a DRF.

 

[3DDave]

There are still 6 degrees of freedom that are controlled even if there are no datums mentioned. Any dimensions that mutually locate the features are identically located and oriented relative to the DRF. The features are already basically located to each other.

I assume this has been clarified - even more than it is now - in the latest attempt at a standard? It wasn't mentioned in the Draft Technical Changes from 08 Nov 17, but maybe since then?

If the single segments are suitable, then abolish composites entirely. I would support that in a heartbeat.

 

[chez311]

There are still 6 degrees of freedom that are controlled even if there are no datums mentioned. Any dimensions that mutually locate the features are identically located and oriented relative to the DRF. The features are already basically located to each other.

I'm not entirely clear on what you're referring to - are you talking about simultaneous requirements in relation to the FRTZF of a composite control or datumless FCF's or both?

 

[CheckerHater]

I am confused - what is the meaning of FRTZF applied to ONE SINGLE HOLE?

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

 

[chez311]

CH.

Thats a good point. The FRTZF of a composite position tolerance isn't doing its primary job of location with a single hole (instead of a pattern of holes where it would be locating each hole in the pattern to each other) so i guess the original scheme in OP's post is inherently not really correct. All the more reason to switch to multiple single segment.

 

[3DDave]

If the original diagram had a single composite tolerance FCF applied to the sequence of holes as a 4X requirement then it would be correct.

So the question is - why would that be interpreted as incorrect at the same time in order to justify using multiple single segments?

Everyone agrees, including the OP, that the conversion shown to allow one or more of the lower callouts to have a different tolerance in the same DRF but as individual callouts, is flawed.

Using SIM REQT corrects that flaw.

Why would that be interpreted as incorrect to justify using single segments?

 

[chez311]

If the original diagram had a single composite tolerance FCF applied to the sequence of holes as a 4X requirement then it would be correct.

So the question is - why would that be interpreted as incorrect at the same time in order to justify using multiple single segments?

If all 4x tolerance zones in the lower FCF/FRTZF could be the same size a single composite tolerance would be perfectly fine, no further discussion needed. I'm a little unsure as to why you're saying thats interpreted as incorrect? None of the discussion about simultaneous requirements invalidates this or requires it be interpreted any differently.

Using SIM REQT corrects that flaw.

Why would that be interpreted as incorrect to justify using single segments?

SIM REQT does not correct that flaw, for the aforementioned reasons that it cannot be used in the lower segments/FRTZF of a composite tolerance to hold simultaneous location/translation between patterns/features not included in that particular composite tolerance. Its not being interpreted as incorrect just to justify using multiple single segments - its inherently incorrect.

 

[axym]

chez311,

I don't mind you referencing my post from the other thread. I'm actually quite pleased to see that you took the "zone translates relative to the DRF" concept, thought through the consequences for the OP drawing, and independently reached exactly the same conclusion that I did (my post was submitted 2 minutes after yours). I see this as a validation that the concept holds water, and that finding the correct underlying geometric principles is a good way to make sense of Y14.5.

3DDave,

I don't think that 4X could be applied to the OP drawing. I believe that Y14.5 requires the features to have the same size and geometric tolerances in order for nX to be applied (as in Fig. 7-49). If they have different sizes and the same geometric tolerances, then n COAXIAL HOLES and a single composite FCF can be applied as in Fig. 7-51.

Just to take this a bit further, I would say that Fig. 7-49 and Fig. 7-51 do not need to be composite FCF's. Two single segment FCF's would have sufficed, and would have been simpler. The special rules associated with the lower segment of the composite FCF (the datums controlling only rotational DOF's, and simultaneous requirements not applying by default) don't have any effect in these cases. There are no datum features referenced in the lower segments, and there are no other FCF's to not have simultaneous requirements with. This doesn't mean that composite FCF's are useless and should be eliminated - there are applications where composite FCF's are very useful, just not in Fig. 7-49 and 7-51. Fig. 7-50 is a good example, where the lower segment refines the orientation of the 4-hole pattern relative to the DRF.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[3DDave]

Evan,

There is still the case of individual sizes and individual geometric tolerances and not being able to use individual segments when multiple datums are duplicated from upper segments. Which my generalization covers and single segments and "n COAXIAL FEATURES" do not, at least not without applying the Voelcker extensions, of which there are no coaxial examples.

"If the single segments are suitable, then abolish composites entirely. I would support that in a heartbeat."

Take set A of all cases that composite tolerances handle and set B of all cases that using single segments handle, B, and IF all of A is within B, then abolish A completely. Using the Voelcker extension this is possible. Since the Voelcker extensions make the requirements explicit, and therefore simpler to interpret, they should be the preferred method, however I expect that few people are interested in using them.