Composite FCF - Datums Repeated in Lower Segment

[tmackay]

Hello All,

I have a drawing with a composite feature control frame:

(Upper segment)Dia .0045 (M)/D/H/P
(Lower segment)Dia .0015 (M)/D/P

I thought the lower segment MUST repeat the primary and secondary in the upper segment (if needed).

So I think it should be:
(Upper segment)Dia .0045 (M)/D/H/P
(Lower segment)Dia .0015 (M)/D/H

In ASME Y14.5M-1994, Section 5.4.1.2 says, "In Fig. 5-20, the lower segment of the composite feature control frame repeats datums A and B." But that's all I could find and that's not going to win my argument.

First, am I correct by thinking this ... then, does anyone know of a better area to point me to in the standard?

 

[pmarc]

Yes, your thinking is correct. If this is composite callout (not two single segment callouts) the datums specified in the lower segment must be in the same order of precedence as specified in the upper segment. The last sentence in paragraph 5.4.1(b) and the note is what you probably need.

 

[tmackay]

Perfect - you are awesome!

Ref. last sentence in 5.4.1(b):
Where datum references are specified,
one or more of the datums specified in the upper
segment of the frame are repeated, as applicable, and
in the same order of precedence, to govern the orientation
of the FRTZF.

 

[SeasonLee]

pmarc: Would you please kindly interpret what's the meaning of "liberation-within-given-limits of the FRTZF" on the Note page 95, its hard to understand it for me.
Thanks

Season

 

[pmarc]

Well, my understanding of the "liberation-within-given-limits of the FRTZF" is that by definition the feature-relating tolerance zone framework (FRTZF) is free to float (translate and rotate) within the pattern-locating tolerance zone framework (PLTZF). And even though some rotational degrees of freedom of the FRTZF may be constrained (depending on presence or absence of datum references in the lower segment of composite FCF), we can say that the FRTZF is liberated within given limits, that is within limits defined by the PLTZF.

Does that answer your question?

 

[SeasonLee]

Thanks, pmarc.

Season