Features Of Size Question 1

[fsincox]

Gentlemen,
I am curious if the interpretation of the ASME Y14.5 standard is the same for all others but me on the issue of Features of Size (ASME Y15.4-1.3.17, 1992). I had never interpreted the “or a set of two opposed elements or opposed parallel surfaces”. To mean the surfaces had to be “directly” opposed, so to speak. This is the way one of the big names teaches it. I also know there is dissent among the ranks on various issues in the standard. I just wondered what others think. Say something like this:

_____________
\
\
\
\_____________

 

[fcsuper]

By my understanding, your example is not a feature of size. Feature of size would a rod, ball or slab.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[Belanger]

The Y14.5 standard thinks of a "feature of size" as being something where the elements are directly opposed. In the 1982 edition, they didn't mention "opposed," so that was included in 1994. Some were hoping that the word "directly" would be added in the 2009 edition, but it was not to be.

The 2009 edition did embellish things by separating FOS into "regular" and "irregular" features of size, but even the irregular FOS doesn't help with your sketch.

A helpful hint for me is that something is a FOS if it can be measured with calipers or a micrometer (but without creating an extension of the surface to make in opposed).

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

http://www.gdtseminars.com

 

[powerhound]

By the 1994 standard, your example is not a feature of size.

Powerhound, GDTP T-0419
Production Manager
Inventor 2010
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[SeasonLee]

A figure is worth than thousands of words, please look at the attached fig for more information about the opposed side.

As mentioned by Belanger, caliper rule is a good way for you to identify the FOS, you may get further information on the link below.

http://www.tec-ease.com/tips/jul-07.htm

SeasonLee

 

[SeasonLee]

Oops,here is the attached opposed side .

SeasonLee

 

[fsincox]

Thanks, guys for your input. Seasonlee, I enjoyed the illustration you added as it almost helps me make the point that it seems like a very fine line.
I think this was also the issue with my confusion in the post on “How to measure a feature of size”.
Belanger, thanks also for your mention of the ‘82 standard. The ‘82 standard is the one I was trained on and the one we reference at the place I currently work, I will not even go into that now. This subtle difference, the addition of the word opposing, did not really change my interpretation, as it does not say “directly opposing”.
As with all legal issues, I understand that fine lines sometimes need to be drawn and should that, in fact, be the correct interpretation, as a long time supporter of the standard, I will be forced to accept it. Please understand, it is my nature to oppose reading things into places that are not really there. As far as people who write books to tell you what the “bible” says, they are entitled to have their opinions. I have heard of meetings of the committee and I know there is sometimes dissent on issues brought up there. I believe the purpose of leaving something like that unstated, as you seem to indicate, may be to be to allow for some flexibility.

 

[fcsuper]

I'm not sure there is a distinction between "directly opposed" and "opposed". It seems that adding "directly" is somewhat of a tautology.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[fsincox]

Well, I must admit after reviewing the '82 standard and the '94 I am forced to the conclusion that they must have meant something by adding that word in.
Thanks all.

 

[Belanger]

Matt -- I agree that "opposed" should be clear, but with legal language you want to make it impossible to misinterpret.

For instance, Jack could be facing west and Jill could be facing east, so they are "opposed." But if I add another detail that Jack is in New York and Jill is in Atlanta, they cannot be "directly opposed."

Just felt like being the Devil's advocate today...

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

http://www.gdtseminars.com

 

[fcsuper]

I wouldn't say they are opposed until I know their spacial location to each other. Otherwise, I would just say they are facing different directions.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[Belanger]

During a discussion today with a few colleagues, another detail of the new standard came to light that makes me want to amend our explanation above of a "feature of size."

It might be easy to say that a feature of size is anything with opposing sides that can be "grabbed" with calipers -- I've often explained it that way. But the new standard is extra careful to say that it must also be something that is "associated with a directly toleranced dimension."

This means that you can have something that passes the calipers test for a FOS but it's not really a FOS because it lacks a directly toleranced dimension. I'm thinking specifically of a width where a basic dimension is used for the width and then a profile tolerance is used on one or both sides to control the width.

So we can never really say that anything is a FOS until we see the drawing for it. Thoughts?

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

http://www.gdtseminars.com

 

[CheckerRon]

Belanger, your last post re: directly toleranced dimensions raises a question in my mind on SeasonLee's sample above. Wouldn't you say that dimension A is a directly toleranced dimension in all three examples, directly opposed or not?
I can envision fitting dimension A on all 3 examples into a slot feature on a mating part, thus giving a "feature of size" element to deal with.
What do y'all think?

 

[CheckerRon]

Let me throw another monkey wrench into the works. What if I need to make dimension A width a symmetry datum for other symmetrical features, but the the 2 sides of dimension A are not directly oppoded so that I can put a calipers or mic across them. Isn't it still a feature od size? Bottom line is that I think figures 1 and 2 in Seasonlee's sketch are also features of size for dimension A. I can clamp them between two gage blocks on a surface plate and measure them---Right?

 

[CheckerRon]

Using the new word fcsuper just taught me, are the 3 dimension A's just tautologies?

 

[drawoh]

Belanger,

I agree with your Nov[ ]02 post. Much of this is design intent. If I apply a dimension and tolerance to a rectangular hole, I am controlling the size of the hole separately from the location of the hole. There are all sorts of ways to do this, but it results in a feature of size.

If I dimension and tolerance both sides of the hole from a common datum, then you can assume I am not very interested in the size of the hole.

JHG

 

[Belanger]

CheckerRon,

I would say that in SeasonLee's picture, the first two examples are still not features of size. There are two conditions that have to be met: the surfaces must be directly opposed, and they have to be directly toleranced (the title block tolerance counts as directly toleranced for what we're talking about). His first two examples fail the first test -- I think that was the point of the graphic.

Also, it's not possible to make the width a datum in those first two examples, since a datum must be derived from either a surface or a feature of size.

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

http://www.gdtseminars.com

 

[CheckerRon]

Thanks, John-Paul. In kicking these ideas around with my colleagues, we came to the same conclusion as you, that the first two examples are really not features of size. Para 1.3.17 of 1994 ed. seems to say that, and the expanded explanations in 1.3.32 of 2009 clarify it for us.

 

[drawoh]

Let me throw another monkey wrench into the works. What if I need to make dimension A width a symmetry datum for other symmetrical features, but the the 2 sides of dimension A are not directly oppoded so that I can put a calipers or mic across them. Isn't it still a feature of size? ...

Again, we are up against design intent. There must be some reason I would want to use the feature as a symmetrical datum other than sheer perversity and/or cluelessness. Presumably, there is a mating feature on the final assembly to which this discussion also applies.

What is wrong with using a height verner to measure each face from the datum and then calculating the distance between the faces?

JHG

 

[fsincox]

the ASME definition also includes "elements" by that definition wouldn't example 2 be OK because it has opposing points?