Features of Size question

[Andrew T]

I have been taking an online test per ASME Y14.5 - 2009 and keep getting this question wrong. The test does not say what the correct answer is.

Per the attached image, the question asks to describe each dimension as:

a) a regular feature of size
b) an irregular feature of size

The 1.000 diameter is obviously a regular FOS. I am screwing up somewhere with the other three dimensions.

my current understanding of FOS leads me to this answer (which was incorrect):
1.000 dia = regular FOS
1.500 dia = irregular FOS
1.250 dia = irregular FOS
3X .200 width = irregular FOS

Could someone please enlighten me to the correct answer and why?

Thanks!!!features of size examples.pdf

[Kelly_Bramble]

Ok, give me a few hours to get on and off this flight and I'll give you my best answer...

In the meantime, revisit ASME Y14.5-2009 paragraph 1.3.32.1 and 1.3.32.2...

[Kelly_Bramble]

So as a side note, The exam is currently to the 1994 edition of the Y14.5 standard.

The concepts of:

a) a regular feature of size
b) an irregular feature of size

Were introduced in ASME Y14.5-2009 standard.

So, you're studying to take the test for which standard?

[Andrew T]

I am currently studying both standards. I plan to take the tech. level certification test per the 1994 standard some time this year. But I also want to know the 2009 standard. I found an online skills assessment test written around the 2009 standard and this question stumped me.

My company has recently decided to implement GD&T. We have decided to use the 2009 standard. Currently we have no one certified and only a few with GD&T experience from past jobs. I have been tapped to become our in-house expert. I have been studying seriously since January. They also want me to lead GD&T study sessions with our R&D, MFG, and QA engineers once I feel I am capable to answer the typical questions that can be expected from beginners.

I have read the Cogorno textbook and the Meadows textbook, along with the 1994, 2009 standard as well as Y14.8.

So, long story short, I want/need to know it all. I would appreciate if you can clear this topic up for me.

[Kelly_Bramble]

Regular Feature of Size; one cylindrical or spherical surface, one circular element, and a set of two opposed parallel elements or opposed parallel surfaces, each of which is associated with a directly toleranced dimension.

A key word here would be "one" and two opposed parallel elements or surfaces would clearly be a tab or slot.

So, the internal Dia. 1.000 is a Regular Feature of Size because it is "one cylinder" and the three tab features width .200 are a Regular Feature of Size because each tab feature has "a set of opposed parallel surfaces" as well.

---

Irregular Feature of Size; the two types of irregular features of size are as follows:


a) a directly toleranced feature or collection of features that may contain or be contained by an actual mating envelope that is a sphere, cylinder, or pair or parallel planes.

Key words here are "collection of features" which means more than one type of feature. Also, "contained by an actual mating envelope".


b) a directly toleranced feature or collection of features that may contain or be contained by an actual mating envelope other than a sphere, cylinder, or a pair or parallel planes.

Here again key words "other than a sphere, cylinder, or a pair or parallel planes." which means everything else that might exist in the universe.

So, the "a" or Irregular Feature of Size definition should include the Dia. 1.500 implied mating envelope diameter shown by the center line (should be a phantom line) that includes the outer surface of the three tab features.

The Dia. 1.250 is not really a feature of size since we don't have any indication that we are to include the other two partial radius's. If we had a Continuous Feature symbol associated with the dimension it could be an Irregular Feature of Size.

[Kelly_Bramble]

Nothing against the books you mentioned (feel free to study my books as well) - being that I did pass the ASME Senior Level Certification test back in 1997, on the my first try and only missed one question...

I strongly recommend that you study the ACTUAL standards, both the 1994 and 2009. Study them very very hard.. Don't worry too much about application - the test is on the standard, not on how designers, engineers, machinist and inspectors apply the standard.

[Andrew T]

I have attached a more comprehensive drawing to further this conversation.

The 3X .200 tabs are now a datum feature. Do the tabs now become an irregular datum feature of size since these three tabs, together, make up datum feature C?

I understand, and agree, that a tab is a regular feature of size. But a pattern of tabs should be an irregular feature of size since we are now considering more than a single set of opposed planes. Correct? This is how I had always understood the question, that all three tabs were being considered at once.

[Kelly_Bramble]

The 3X .200 tabs are now a datum feature. Do the tabs now become an irregular datum feature of size since these three tabs, together, make up datum feature C?

No, they are verified independently as FOS.. The 3X is just for simplicity..

When used as a Datum reference ... the jury is out for me though my initial thoughts are that it is WHEN simulated as Datum C for establishing a DRF.


1.000 dia = regular FOS
1.500 dia = irregular FOS
1.250 dia = irregular FOS
.200 width (3 Places) = regular FOS

or

.200 width (3 Places) used as Datum C = irregular FOS