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 & 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.
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.
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 -- 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