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needhelp with composite box

needhelp with composite box

needhelp with composite box

(OP)
I have tried several types of composite boxes, but none seem to describe what I want, or at least they dont look right to me.
My intent is to have the .375 dia have a position tolerance of .014 from datum -a- but .003 from centerline of datum -b-.
I also want an orientation tolerance of .003 for perp to -a- and perp to -c-.
What would that

RE: needhelp with composite box

1. I need to ask which version of Y14.5 (I assume you use this standard) are you using? It is because the most common perception is that per '94 edition a composite FCF cannot contain more than 2 segments. Per '09 edition this limitation is no longer valid - a composite FCF may contain as many segments as it is possible and reasonable.

2. I do not exactly understand what you mean by: "I also want an orientation tolerance of .003 for perp to -a- and perp to -c-." Does this requirement apply to the pattern of holes too? I am somehow having a trouble to picture the holes being perpendicular to A. Perhaps you meant "parallel to A"?

3. We do not know datum features order of precedence. Should we assume that A is your primary datum feature, B secondary and C tertiary? If that is the case, I would encode your: "My intent is to have the .375 dia have a position tolerance of .014 from datum -a- but .003 from centerline of datum -b-" in composite FCF:
|pos|dia. .014|A|B|C|
| |dia. .003|A|B|
The callout may change depending on your answers about 1 and 2.

RE: needhelp with composite box

One caveat to my reply.
If you want to control location of the pattern to B within .003, this would rather have to be two-single segment callouts, that is:
|pos|dia. .014|A|B|C|
|pos|dia. .003|A|B|

My apologies for this confusion.

RE: needhelp with composite box

ronj100
See slide 3 for a possible solution.
I believe you may have your datum features mixed up for their functional influence on the assembly. Functionally I don't think that the shoulder surface can arrest the two rotational degrees-of-freedom away from the long perpendicular cylinder adjacent to it.

RE: needhelp with composite box

Paul,
I am really interested to hear why you think that datum features in OP's drawing were mixed up.
First of all, he did not specify datum features order of precedence (alphabetical order doesn't automatically mean that A is primary, B secondary, etc.), so technically there is nothing to mix up.
Secondly, how can you say that functionally surface A can't arrest the two rotational degrees of freedom without really knowing how the counterpart looks like?

RE: needhelp with composite box

pmark,
You are correct he didn't specify... I said "may have" not "are"(were) and I will stick with my functional assessment. I believe as I have said before get the datums right first and the rest will fall in place.

RE: needhelp with composite box

Paul,
I am just staring at fig. 7-35 in Y14.5-2009 (fig. 5-62 in Y14.5M-1994). What, in your opinion, was the decisive factor in selecting shoulder surface as primary datum feature there? Was it solely shoulder length to thread length ratio or was it maybe something else? Please do not take it as a critique, I just want to understand your certainty about functional assessment of datum features without knowing how this part looks in assembly.

RE: needhelp with composite box

pmarc,
Clamp load(maybe 800+ Kg)assisted by shank clearance maybe 3/4 MM all around... Just guessing... In ronj100's clevis the translation along the axis may actually be a width with clearance or it may have some sort of gravity assisted ramp for self closing... I don't Know!!! That clevis shank is twice as long as the surface is wide and I would guess it has minimal clearance in the assembly.

When I counsel designers in selecting the datum features I tell them to examine what wins in constraining the three rotation and three rotational DPF's for the part you are detailing in the assembly or function. Which ever does the most is primary... if tied which ever does the most rotations typically wins... and the remaining follow accordingly. Custom DRFs can be very powerful but it is important to understand the basics first.

RE: needhelp with composite box

Quote:

examine what wins in constraining the three rotation and three rotational DPF's for the part you are detailing in the assembly or function.
should be... examine what wins in constraining the three rotation and three translational Degrees-Of-Freedom for the part you are detailing in the assembly or function.

RE: needhelp with composite box

(OP)
I am using 1994.
Yes, I mean the holes are parallel to -A-, not perp (my bad).
Yes, the shaft should be -A-. (my bad again).

I am looking at pauljacksons solution. His suggestion may answer my problem. I thought it was possible to meet all my conditions with a composite frame. I may be asking to much.

I am making a manufacturing process print for the shop to mill the slot and dill/bore the holes. The customer print (see link) has, in my opinion, so few controls that I am sure if I do not control the design tighter that I could meet print but send the customer unusable parts.I have to make these judgments all the time to give the customer a good part even though thier print is woefully underdefined.

FYI, the print is xxx = +/-.010 xx= +/-.03. No info in title block as to tolerances of features in relation to centerlines.

https://dl.dropboxusercontent.com/u/45474807/cust%...

RE: needhelp with composite box

Composite FCF may still be needed, if there is a requirement to keep both holes coaxial within a tolerance zone smaller than the one defined by |pos.|dia. .003|A|B| callout.

RE: needhelp with composite box

Season,
In my opinion option on the left is better choice, because it controls position of the pattern within .003 relative to datum axis, which is one of the goals, as far as I understand. Option on the right will not do it.

As a matter of fact the very same effect would be achieved if option on the left was modified in a way that first FCF was still single segment FCF, but second and third segments were combined into one composite FCF.

RE: needhelp with composite box

Season,
Just to have everything clear, you placed the three options on a drawing that contains datum features specified in non-functional order of precedence, as we already agreed with Paul and ronj100. I just hope this isn't the reason why you are asking for further clarification.

Nevertheless, options #1 and #3 are equal in meaning. I just prefer option #3, because for prints following Y14.5M-1994 you can meet folks which are really not comfortable with single segment positional FCFs containing no datum references, like it is done in option #1. So why to make them uncomfortable? No datum references in lower portion of composite positional FCF are clearly specified in Y14.5M-1994 (see for instance fig. 5-51), so this is much safer way to go, in my opinion. Especially if you want to avoid dozens of questions later on.

RE: needhelp with composite box

(OP)
Hey,
great stuff. Really.
I would have never attemped option 3 because I never thought of combining a single segment feature control frame with a separate composite control frame for the same feature.
I could not find an example after browsing through my ASME or Lowell Foster books. Anything in 1994 specifically allow this or disallow it?

RE: needhelp with composite box

pmarc, thanks for your comments.

I am not asking for further clarification, I just want to know what is your considerations on your recommendation option #3, I am pretty sure a lot folks (include me) will have a little confused on option #1 and #3, and what is the differences between them.

Season

RE: needhelp with composite box

(OP)
I think I understand option#1.
The first two segments are decribed in 5-26 of 1994.
The third is in 5-51, although that is a composite example the intention can be reproduced with single segment frames due to the lack of a datum.
Right or wrong?

RE: needhelp with composite box

Quote (ronj100)

I would have never attemped option 3 because I never thought of combining a single segment feature control frame with a separate composite control frame for the same feature.

You would have to combine a single segment FCF with a separate composite FCF, if your additional functional requirement encoded in lower portion of the composite FCF was to control orientation (perpendicularity) of the pattern to datum axis A AND coaxiality of the holes within the pattern tighter than location to datum axis A defined in upper segment of the composite FCF. In that case option #1 would be useless, but option #3 - with addition of A to lower segment of the composite FCF - would work fine.

But like I said, options #1 and #3, as they are now, are equal. If you feel better with option #1, use it.

RE: needhelp with composite box

This whole no datums for position thing really bothers me, another glitch in the 94 standard. Position has been used this way since MIL-STD-8(1959?). My bet is that if the 94 standard meant anything by it it was to prclude these old ways not the ways we are looking at now, thus the need for re-evaluation in 2009.
This is a perfect example of why, we need, outside "the book" thinking. They make mistakes too.
Frank

RE: needhelp with composite box

(OP)
Gee, I dunno.
I guess the no datum kinda made sense to me when I thought about it.
If there is a position callout of a feature and no datum, than the relationship is to the feature itself, not something else (like a datum).
And, of course, this can only be multilple features of the same geometry in line with each other. Golly, I wonder if you had multiple forms of any kind in alignment that such a non-datum callout would work. A composite box for form? Possibly.
Just thinking out of the book. lol.

RE: needhelp with composite box

ronj100,
I like you already :)
Frank

RE: needhelp with composite box

I my opinion those of us trying to get work done should not be subjected to punishment by the committee for years of their inability to agree and their poor examples, something like this is the perfect example. It was OK, then, some think it is not, later it is, again. They just screwed up.
Frank

RE: needhelp with composite box

(OP)
Years ago I took my GD&T classes from Lowell Foster (He is one of the authors of ASME Y14.5 1994). Only recently I returned to the field, so I am rusty on my GD&T. But I definitly remember Lowell telling us that the concepts of GD&T, if understood, had much more potential as well as symbolic representation possible than what was presented in the Standard. The Standard was just to get the ball rolling in the industry. Lowell actually encouraged us to think up additional logical ways to represent location or orientation as long as it built upon the standard. So my point is that if a GD&T callout makes sense according to the concepts that the standards are explaining, but that specific callout is not represented in the standard, is it always to be wrong?

That goes back to my question to pmarc which he has not answered. I could not find an example of option#3 after browsing through my ASME or Lowell Foster books. Anything in 1994 specifically allow or disallow combining a single segment FCF with a separate composite control frame as illustrated in option#3?

RE: needhelp with composite box

Ron,
I was trained by another student of Foster's and was also given the impression that the standard was a work in progress and not an absolute limit definition. That was when the ISO and ASME were going to live happily ever after, in the 1994 version.
You are asking pmarc for the impossible, they did not yet see the possiblities or, at the very least, let it be known to the rest of us at that time.
I have books by committee people that discuss it and those of us that were concerned with defining functional requirements of parts saw it had to be coming.
Mark Foster seems to be of the same vein, I wonder if he is related?
Frank

RE: needhelp with composite box

Two points,
First, to be fair a standard is by definition an attempt to keep everyone on the same page so I do understand to some extent the rigidity is required or you have no standard at all.
Second, I agree that the old examples of position without datums were in most cases just examples of bad practice, even when the early standards did it, the attempt at rectifying that in 1994 but then rectifying that new error in 2009 should be enough to see it should be disregarded, IMHO.

RE: needhelp with composite box

I haven't been following the main discussion here, but I wonder why Frank (and others?) have a problem with a position tolerance with no datum references. The example given was Fig. 5-51 of the 1994 standard; suppose we lopped off the upper tier and just had the 0.15 position? I see no problem with that. Maybe not a wise design, but it seems legal because it just positions the holes to each other only.

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

RE: needhelp with composite box

JP,
Sorry to confuse, I am saying it is definitely OK, IMHO.
Frank

RE: needhelp with composite box

No problem -- I guess that's what happens when I jump in mid-stream. I'll butt out again...

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

RE: needhelp with composite box

JP,
I am not a writer and reading back I think I can see that I may not be expressing myself completely and clearly. That is no fault of yours.
I am also actually harking back to another thread, here, that was discussing some "1994 prohibition against position without datum references" that completely through me for a loop. Thankfully, the committee has come to its senses since then! Thus my position being if it was OK, then not OK, then OK again, they most likely just made a mistake!
Frank

RE: needhelp with composite box

@ronj100,
First of all, do not expect to find each and every case in the standard or in any other publication.

Nothing in '94 standard, as far as I can tell, allows or disallows "combining a single segment FCF with a separate composite control frame". However, in my post from 4 Sep 13 16:01 I gave you one example, where this combination would be the only way to grasp functional intent. In my opinion this solution would not violate any of GD&T rules defined by the standard.

Nothing in '94 standard, as far as I can tell, allows or disallows using single segment FCF without datum feature references too. However, since there is no example in the standard showing its applicability, yet there are examples showing that position without datum feature references can be used in composite callouts, I prefer option #3. Like I said, there are many people, sometimes GD&T authorities even, claiming that when something is not explicitly shown in the standard, it is illegal. I am not amongst them, thus I also said you can choose option #1 or option #3 depending on your preferences.

As for stand-alone positional callouts without datum references applied to patterns of features (that is where there are no other geometric tolerances controlling location of the pattern), I am all for it as long as the pattern serves as primary datum feature. (Again, this concept is not shown in '94 standard, but is explained in '09 edition). In any other case, this would be incomplete drawing specification. Location of such pattern through directly toleranced linear dimension(s) is very far from naming it "clear & unambiguous".

RE: needhelp with composite box

I believe the practice in pmarcs last paragraph is all the committee is trying to get away from. A practice you will see alot on old drawings and, as I pointed out, in the older standards themselves.
Frank

RE: needhelp with composite box

(OP)
Thanks pmarc,
I really appreciate the clarifications and explanations. They help much.

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