composite position tolerance (in composite feature control frame vs separate feature control frame) 1

[vik922]

Hi,
Greetings!
can somebody explain clearly what is the difference between composite position tolerance in composite feature control frame and composite position tolerance in separate feature control frame(see attached image).
i didn't get much understanding from standard.

 

[greenimi]

http://www.tec-ease.com/gdt-tips-view.php?q=123

See this

 

[greenimi]

There are also plenty of youtube videos from Tec-Ease,
Here is just one example:

https://www.youtube.com/watch?v=GFgoctqNkRo

 

[vik922]

Thanks greenimi !!
that helped a lot

 

[AndrewTT]

The standard is not a great text book. I found learning easier when consulting materials that are meant to be instruction for newbies and not from reading material that is more meant to be reference for people already knowledgeable of the subject.

 

[vik922]

I agree with you Andrew.
can you please suggest some good books for learning the 'GD&T' and stack up.
thanks.

 

[AndrewTT]

I "learned" (am still learning) GD&T via:
--------------
-the ASME standard (cons of this already discussed)
-the Cogorno text book (many, many errors in this book but still good for the beginner)
-the Cogorno instructor's materials (3 tests w/ answers)
-the Meadows text book (I would read Cogorno first)
-the Meadows workbook (read his textbook first)
-Tec-Ease vids on youtube
-this forum
-consultant brought in to discuss application of GD&T to the parts my company makes
-------------
There are many more books and resources available but I have not read them, so I have no opinion.

If you buy the Cogorno book I can send you a list of corrections that I have compiled.

I am just beginning to study stack.

 

[Nescius]

AndrewTT,

I'd really appreciate it if you made your Cogorno book error list available to us here. I have only the standard and a pile of free resources I've gathered, but the Cogorno book is at the top of my list because I found his newsletters to be very helpful (

http://www.ttc-cogorno.com/Newsletters/index.htm).

 

[AndrewTT]

The corrigenda is attached.

Please note that I have not made corrections to the "chapter review" (fill in the blank) sections of the book. There may be errors in these sections also. I have only noted the errors in the text of the chapters and the end of chapter problems. Also my list is not complete. I find more errors every time I reread this book.

One last thing, some of the text that I draw attention to is not necessarily incorrect but some of the beginning students at my work were confused by the author's wording so I offered alternative wording (hopefully not alternative facts...). This is only in an effort to make clear the intention of the author, as I interpreted it, for my coworkers.

 

[Nescius]

Thanks, AndrewTT. Also, I learned what in tarnation "corrigenda" are.

 

[vik922]

Thank you Andrew for recommendations!!

 

[AndrewTT]

New error noted in figure 8-24 on page 151. Datum A can be left off the the FCF for the c'bore position (per figure 7-26 of Y14.5-2009).

 

[pmarc]

Technically, what Cogorno shows is not an error, just like there is no error in fig. 7-37 in Y14.5-2009.

 

[Belanger]

I don't have Cogorno's book, but there actually is an error in Fig. 7-37, pmarc. They forgot the diameter symbol which belongs in front of the 79.4.


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

 

[pmarc]

Although I wasn't thinking about the entire fig. 7-37, but only about the reference to primary datum feature A in the lower position FCF applied to the pattern of 4 dia. 3.6 holes, it is still nice catch, J-P.

To picture Cogorno's example, take fig. 7-26 from the 2009 standard and add A as primary datum feature reference to the position callout for c'bores.

 

[AndrewTT]

Maybe its a question of the design intent of the part. If the intent of figure 7-26 is to have each c'bore tied to its respective hole then calling out [A] [C@MMB] has a different meaning than only calling out [C@MMB] for the position of the c'bores, yes? That difference being a tolerance zone for the c'bore that is oriented perpendicular to A and located from C as opposed to a tolerance zone that is oriented parallel to C and located from C. Keeping in mind that the datum feature C could be produced using all of its acceptable position error manifested as orientation error w.r.t. datum A.

If the design intent is to have each c'bore located from its respective hole but oriented w.r.t. datum A then I would agree that [A] [C@MMB] is correct.

Thoughts?

 

[pmarc]

Well said, Andrew.

Whenever possible, function / design intent should be the main driver in choosing dimensioning and tolerancing schemes.