Pattern of holes as reference and function of frame with profile in a special condition

[roberto1brazil]

Hello everybody.
Please, I need your support regarding the sketch attached. It is a simplified drawing of a shroud of turbine. Only the main features are represented in the sketch. The aim of drawing is to supply information to machine a lobule located at 30° from hole “O” at opposite position ( section E-E). There is a fixture that locate the part 0,15 mm off center (in the angle indicated) in order to machine the internal lobule. The part is supplied with an initial internal diameter ranging from 237,65 to 237,70. The average wall thickness is around 1,45 mm. The origin reference center (B) is established by the three holes diameter 7 in the basic diameter of 282 mm.
In a practical way, the internal lobule is done moving the cutter to outside little by little until the thickness reaching near 1,3 mm thickness at position of section E-E. In fact it is done controlling the final thickness.
Doubts:
1- Why the reference B is written as B-B inside the frames?
2- What does it mean the frame identified with interrogation (?) in the sketch and what would be its function?
Thanks for any comments.

Roberto1brazil

 

[Belanger]

This looks to be ISO style of GD&T (because of the use of CZ). In both ISO and ASME, however, there is no provision for having a datum reference B-B. So I have no idea what the intent was -- they probably meant B as a single datum reference (and I would even suggest using an M modifier on that datum reference since it's created from a pattern of holes).

I also don't have a good answer for your question about that profile tolerance with CZ. All of those profile callouts seems incorrect since we shouldn't apply profile to a radius dimension; we should apply it to the surface. And to further complicate things, they have two composite profile tolerance frames also applied to the radii. Ugh.

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

 

[mkcski]

roberto1brazil:

Question 1: I have never seen a multiple-feature datum with repeated letters. It is not discussed in Y14.5, so the interpretation is questionable. It might be an ISO thing, but I doubt it. Could they be pointing out that there are three holes that establish datum B - then why not three B's.

Question 2: I have no idea. It appears to be redundant and conflicts with the other feature control frames with profile.

Sorry I cannot offer more. Maybe others will chime-in.

Certified Sr. GD&T Professional

 

[mkcski]

roberto1brazil:

I am also bothered that there is no datum (axis) for "centering" the (3) 7mm holes relative to some other feature on the part - like maybe the OD of the ring.

Certified Sr. GD&T Professional

 

[mkcski]

roberto1brazil:

I agree with J-P that a radius cannot have profile - only a surface can. And the composite profile symbology with "F" appears to be misapplied as well. Can we assume the upper frame is the restrained tolerance and the lower frame is the larger Free-State tolerance.

Certified Sr. GD&T Professional

 

[pmarc]

Here is a couple of excerpts from some of ISO GPS standards (I assume the drawing is per ISO GPS):

1. Meaning of the reference to B-B in the profile tolerance frames - ISO 5459:2011.

http://files.engineering.com/getfil...ac0-420c-bcfa-626ff2ebc45f&file=capture_1.PNG

So with regard to this item the only thing that looks incorect in the sketch given by OP is '3X' note missing right next to datum feature B symbol.

EDIT: In cases like this, where datum feature symbol is associated with a geometric tolerance frame and the number of features constituting the datum feature is given above the tolerance frame, the '3X' note is not required.

I think the discussion on whether it functionally makes sense to reference pattern of features at RMB (using ASME terminology) or not is, at least for now, beyond the scope of this thread.

2. The meaning of CZ modifier in the profile 0,025 tolerance frame - ISO 1101:2012.

http://files.engineering.com/getfil...676-4a5e-abdd-683ed577066d&file=capture_2.PNG

Per the latest version of ISO 11O1 standard, issued this year, the CZ modifier is no longer called "common zone" but "combined zone".

3. The composite profile tolerance frames associated with both basic radii - ISO 10579:2011.

http://files.engineering.com/getfil...37e-4a38-89c9-9b1ca4bdc302&file=capture_3.PNG

The attached figure does not specifically show usage of profile tolerance, but if we imagine that the surface marked A is not a flat face but an arc, and the feature/surface B is not cylindrical but of a complex shape, profile of a surface tolerance could easily be used instead.

So technically these are not composite profile callouts (in ASME sense). They are just tolerance frames defining the same characteristic (profile of a surface) in different conditions of the part - restrained vs. free state - just like the flatness tolerance frame shown in section E-E. Although here I agree that the profile tolerance frames should not be associated with the radius dimensions but should be applied to surfaces.

 

[Belanger]

Thanks for the clarification on B-B, pmarc. Obviously when it comes to ISO stuff, you're the guy



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

 

[mkcski]

pmarc:

Yes, for sure you are the ISO guy. I do have one ISO vs Y14.5 question regarding the B-B symbology. The Y14.5 interpretation o fthe dash between letters is a multiple feature datum. Considering the interpretation from 5459 in your post, is the ISO symbology different for multiple feature datums? If not, how do you tell the difference between for example B-B and A-B?

Certified Sr. GD&T Professional

 

[pmarc]

mkcski,

I am not really sure I understand your questions.

The rule in ISO is that if datum is derived from a single datum feature, then it is always indicated by one datum letter in the tolerance frame referencing that datum. If datum is derived from more than one datum feature, then that is always indicated by A-B or B-B or A-B-C etc. Technically, in the datum pattern example from my previous post one could use five different datum feature symbols for each hole and then reference to all five, e.g. A-B-C-D-E, in the tolerance frame, and that would change nothing in terms of datum establishment (compared to A-A). But obviously this would not be the most efficient way of doing things.

 

[mkcski]

pmarc:

Technically, in the datum pattern example from my previous post one could use five different datum feature symbols for each hole and then reference to all five, e.g. A-B-C-D-E, in the tolerance frame, and that would change nothing in terms of datum establishment (compared to A-A)

Let me try again. Given the info in your latest statement quoted above: considering the OP drawing which has the pattern of three holes specified as datum B (by attaching the foot to the FCF), why in the profile FCF wouldn't it say B-B-B for the three holes (one letter for each feature) instead of B-B?

Or.. given the ISO symbology in 5459, is B-B used to represent a pattern of features (holes in this case) as a datum no matter how many features are in the pattern?




Certified Sr. GD&T Professional

 

[pmarc]

mkcski,

Now it is perfectly clear to me what you asked for.

Per ISO GPS if a group of two or more features is assigned datum feature and the datum feature is represented by a single letter, say A, then the datum reference in the tolerance frame should be A-A regardless of the number of features constituting the datum feature. So if a group of 5 holes is datum feature A (as shown in the example from ISO 5459), the datum reference should still be A-A, not A-A-A-A-A.

 

[mkcski]

pmarc:

Thanks for being patient. To me this is another example of the "confusion" offered by ISO. So, one letter "A" in the datum feature symbol (square)is represented by "A-A" in the FCF. Really? Why not use one letter like Y14.5 and avoid the confusion? Oh well. Maybe over time the two standards will evolve into one, combining the best from each.

Certified Sr. GD&T Professional

 

[pmarc]

mkscki,

I don't really have good answer to that question. To me it looks like they really wanted to distinguish between datums derived from a single feature and datums derived from multiple features, and that is why they came up with this method.

Perhaps this will dissapoint you even more, but at this point of time, in 2017, I firmly believe that unification of ASME and ISO standards is not going to happen, at least not in another half of century or so. I have access to some of the recent versions of the most important ISO GPS standards, like 8015, 1101, 14405, 1660, 2692, 5458, 5459 etc. I also have the draft of the next version of Y14.5. Both standards are getting more and more complex but the way the complexity is handled is very different and it does not look like there is even a trace of wish to find similar solutions.

 

[3DDave]

There is practically a law of nature that says overlapping standards cannot be voluntarily merged. To do so means an end to one of the standards organizations. There is also a tendency to increase complexity in order for the members to have something new to discuss.

 

[greenimi]

"There is also a tendency to increase complexity in order for the members to have something new to discuss"..........And the trainers and consulting companies have more customers....with greater chance of making the standard irelevant to the real world.......

 

[roberto1brazil]

Hi everybody.
Thanks all a lot for your attention. The drawing came from France and so I believe that it was ISO. Sorry for don't mention it. I am really glad for all comments. I was without internet since yesterday, and only today I was able to read.
Best regards
Roberto

 

[mkcski]

pamrc:

Thanks for the window into the future. I was being hopeful more than realistic. However, begin pragmatic, but not pessimistic, the influence of the US in the global manufacturing arena is diminishing. I suspect over time - decades as you said - ISO may become more prevalent than it is now - maybe even superseding Y14.5 as the defacto world Standard. Who knows.

Of note: I was at a Y14.5 Committee meeting a few years ago. I never realized it, but the Standards committees are "staffed" by volunteers and their attendance is financed by the organizations that employ them - there are government labs and educational institutions too. It was noted by the Chairman - Bruce Wilson at that time - that some attendees would not be attending as their organizations were no longer be supporting their attendance. Maybe this is a sign of something more systemic. Also, less support might be why the time between revision releases is longer.

Certified Sr. GD&T Professional

 

[Belanger]

At $200 for a paperback book (Y14.5), you'd think that ASME could afford to cover some costs, not the employers!

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

 

[mkcski]

J-P:

ASME most likely pays for the LARGE room at venue the meetings are held and what ever amenities are needed - coffee, tea, donuts. At the meeting I was at there were over 50 persons sitting "behind" the U-shaped table layout that the Committee members were sitting at - a big projection screen was on the 4th side. This was a 3-day event. I noted too that many of the other Y14.XX Committees had smaller meeting rooms reserved - many of the Y14.5 members are on other related Committees.

Certified Sr. GD&T Professional

 

[3DDave]

Linux and Blender (

http://www.blender.org)

are also largely volunteer driven and they come out with new versions frequently. The more obvious difference is that Linux and Blender are very much public about what they are working on and very focused on utility.