Regilar or Irregular F.O.S

[nry67]

I search to understand the real difference between the regular and the irregular feature of size ?

 

[pmarc]

Have you looked at fig. 4-35 in Y14.5-2009? This is, I believe, good visualization of difference between FOS and NFOS.

 

[pmarc]

I should write 'regular FOS and irregular FOS' rather than 'FOS and NFOS'. Sorry for this.

 

[nry67]

Good Morning pmarc,
In fact i had just the ASME-Y14.5M-1994
Can you sent to me the fig. 4-35 in Y14.5-2009?
Please
Thank by advance.
Henri.

 

[pmarc]

Here you are.

http://files.engineering.com/getfil...44b7-bab4-a8c38d676db6&file=irregular_FOS.JPG

 

[nry67]

Ok thank you Pmarc,
also i can put a dimension XX+/-XX in example (d) on fig. 4-35 or it's preferable to use the geometric symbol to describe the fonction ?

 

[pmarc]

I would say you can put typical size dimension XX[±]XX

 

[nry67]

Pmarc, if I understood the irregular FOS, the dimension on my example it's it?

 

[pmarc]

Based on the definitions of regular and irregular features of size given in Y14.5-2009 (para. 1.3.32), I would consider your dimension as regular FOS.

Although upper face of presented part is a plane, the dimension controls the distance between two opposed parallel linear elements of surfaces.

 

[DeanD3W]

Pmarc & nry67,
I think that dimension would be applying to an irregular FOS, since it is constraining a mating envelope of two parallel planes, but the feature is other than two opposed parallel planes or elements.

Dean

 

[nry67]

Hello Dean & Marc,
To clarify the discussion I attach 2 examples of drawing.
Can you to give your opinion for the dimensions with a letters.
"Reg. FOS"
"Irreg. FOS"
or "N/FOS"
Thanks for your help.

 

[pmarc]

Regular FOS - B, E, F, G, H, K, N, O, S, U
NFOS - A, C, D, I, J, L, M, Q, R, T,
I see no irregular FOS on the drawing.

BTW: Is everything OK with the presentation of rectangular feature described by dimensions "F" & "I"? I must say I have some difficulties with visualizing it.

 

[nry67]

Marc, For the dimensions "F" & "I" i remove the edge (see the new document). For the second slide what are your opinion?

 

[nry67]

To me my answer is:
"Reg. FOS": E,F,N,O,V,AA
"Irreg. FOS": B,G,H,K,R,S,U,
"N/FOS": A,C,D,I,J,L,M,Q,T,W,X,Y,Z

 

[pmarc]

Because I already assumed that the edge you removed on second sketch should not be on the first sketch, my answer is still the same.

 

[pmarc]

I didn't notice second page.
For this:
Regular FOS - AA
NFOS - V, X, W, Z
I still see no irregular FOS on the drawing.

 

[pmarc]

There might be however a discussion on "V" since the half circle has one pair of opposed linear elements.

 

[nry67]

Marc, if you agree I waiting the answers of Dean to analyse it.
Thank for your reactivity.

 

[SeasonLee]

The answer from pmarc is exactly right, there isn't any irregular FOS on the slides.

SeasonLee

 

[Belanger]

Pmarc is right.

nry67 -- attached is a snapshot of the actual definitions from ASME Y14.5-2009. First, notice what is required for something to be a feature of size. Think of it this way: if you can grab hold of it with calipers or a micrometer, it is a FOS. But then, FOS can be subdivided into regular and irregular. Your pictures don't seem to have any irregular FOS. (An example would be an octagonal hole; it can be measured with calipers, but it doesn't meet the requirements of a cylindrical surface given in paragraph 1.3.32.1.)

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