Y14.5.1 Standard - Mathematical Definitions

[axym]

Hi All,

The ASME Y14.5.1 standard for Mathematical Definition of Dimensioning and Tolerancing Principles (a.k.a. the "math standard") is in the process of being updated. I was wondering what opinions people had about the existing version (Y14.5.1M-1994). I realize that this document is relatively obscure and that many GD&T users have not had the opportunity to read it.

Specifically, I am looking for opinions on what the existing version did well and what could be improved. In addition, I'm interested to hear what GD&T questions and issues people feel that Y14.5 leaves unresolved and that the math standard should address.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[CheckerHater]

Literally half of the book is dedicated to proving that parallelism, perpendicularity and angularity are all the same, by analyzing ANY possible combination of datum and related feature; and then (you guessed it) it is declared "appendix A" and not the part of the standard.
I think all that effort could be put to better use.

 

[MechNorth]

The only comment that I have is that inspection software doesn't follow the standard in most cases. I applaud the effort, but if it is not used, then is it of value? If it is of value, why isn't ASME doing something to certify compliance with the standard?
And yes, I did actually go thru the standard a while ago. Very "mathy". ;~}

Jim Sykes, P.Eng, GDTP-S
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[fsincox]

Is this the plae to get into: specified tolerance zone shape vs actual control to the stated framework? It is in a implied in a footnote in case 17
Frank

 

[CheckerHater]

Say again?

 

[fsincox]

CH,
This standard is the one I use to support the idea that the tolerance zone shape definition is independant from the control that it is allowed to exert. I use this standard based on case 17, A.3.5, pg 64-65 & Table A-1, pg 50. It does not say, there, it is not allowed or incorrect to use a cylindrical zone despite also noting not having the framework to support it, as stated in note (3), the resulting control is the same!
thread1103-314840
Frank

 

[axym]

CH,

I agree that the appendix on datum feature combinations for orientation control is inordinately lengthy. All that space could probably be put to better use.

Jim,

I agree that inspection software often doesn't follow the standard. There have been informal studies of inspection software's compliance to the standard, but nothing sponsored by ASME. Obviously my opinion is biased, but I would say that the math standard is still valuable even if it is often ignored. It provides a path to determining an "official" actual value for a given geometric characteristic, if one is willing to wade through the math and perform the tedious optimizations that are often necessary. You're right that that Y14.5.1M-1994 was very mathy, and was not written with the "typical" GD&T user in mind.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[CheckerHater]

Frank,

OK, got it! We are actually on the same page.
So much good stuff and then it sais "this is not part of the standard".
Kinda hard to use it to support your case :-(

 

[axym]

Frank,

I don't have the standard in front of me, so I can't look up the sections you referenced until tonight. But the point you are making seems to make sense - that the tolerance zone shape is independent of the control that it is allowed to exert or the framework used to support it. Is this another way of saying that the tolerance zone shape specification is completely independent of the datum feature references? If so, then I agree.

If the independence of the considered feature spec and the DRF spec is a general principle, which I believe it is, then Y14.5.1 would be the place to describe that principle. There are many GD&T principles or "unwritten rules" in Y14.5 that are not stated explicitly, but are defined by examples. I believe that part of the scope of the the math standard, as a basis for the math itself, is to identify and describe these principles and establish a set of rules based on them. The "physics" of Y14.5 GD&T, as it were. Once the underlying rules are established, they can be mathematized for those who are so inclined. The rest of us can just work with the set of rules, to be able to figure out particular cases like the "sphere to a plane" example from the other thread.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[MechNorth]

Evan! I put a smiley face on my post. Of course I think it's useful ... just frustrating that nobody freaking uses it!

Jim Sykes, P.Eng, GDTP-S
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[DeanD3W]

Jim,
I know of one software product that does make use of Y14.5.1 as far as I have been able to tell so far. For me to name that software here wouldn't be appropriate, but I wanted to mention that at least there is one company that did their due research before creating their software product... Where there is one there may be others..? Or, maybe by pointing out this one exception I am supporting your point .

Dean

http://www.d3w-engineering.com

 

[MechNorth]

Dean,
I think you and I may have discussed the exception at the meetings. I know I have with Evan on a couple of occasions. To the best of my knowledge, only that one package is actually using the algorithms. I've challenged a few others and haven't been impressed with their responses.

Jim Sykes, P.Eng, GDTP-S
Profile Services

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