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:

_____________
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[fsincox]

I want to add to what I said above. We use a lot of tapered cone features, most are defined on the drawings by dimensions to directly apposed points we call “gage points”. So, according to what I am reading here these are not features of size then. Personally, I suspect this is why the ASME committee needs to leave flexibility to definitions and simple caliper definitions are not used. I hope they are trying to define standards to work for all kinds of parts not just the simple parts.

 

[fsincox]

I disagree with this whole "a diameter is a feature of size but a radius is not". Talk about confusion, We all knew the circumference of a circle is pi*d or 2*pi*r they were interchangeable now they are not, are you kidding? Until it is stated as such in the standard I am not buying. Give me reason, not someone's rule of thumb. I know it is harder to measure if it is not a whole circle, hey life is tough.

 

[fcsuper]

Take a look at ASME Y14.5 2009 regarding new types of FOS now supported.

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]

fcsuper,
Thanks, It does look like they are preparing to placate people like me. We will have to see how it is generally interpereted.

 

[fsincox]

fcsuper and J-P,
I believe, I was taught in college engineering mechanics that opposed forces, acting not on a common line, create a couple, if opposed really meant to all "directly opposed" there would be no couple created.
Frank

 

[JonSelby]

As I understand it ... ISO standards would suggest that dimension A in fig-1 and fig-2 is redundant and in fig-3 would only apply over the section that is (directly) opposed.

As a result, could you potentially get the condition highlighted in my attached PDF?
Is that correct or am I missing something?

Thanks,
Jon

 

[fsincox]

JonSelby,
I am sorry that I am not as familiar with the ISO standards, I am interested in learning. From what I had read of the ISO (assuming "principle of independency") I thought there would be there is no assumed condition at all. My impression is it would all based on 2-point measurement unless specifically stated on the drawing or as otherwise, say normal process tolerances for a class if this is specified on the drawing. In this case we have only the implied angularity tolerance which may also apply to the parallel surfaces? This example was intended to show the requirements of the ASME standards.
Frank.

 

[MechNorth]

Jon,
Quite arguably, that's also true for the ASME definition of feature of size (regular). I've worked with many companies who didn't realize the subtlety ... then went back and checked ... it was in fact the source of errors because you are projecting a surface out to make a directly opposed point.

Jim Sykes, P.Eng, GDTP-S
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