using a datum and within datum frame using same datum MMC
using a datum and within datum frame using same datum MMC
(OP)
I am looking at a print that has a datum C call out on a hole. The hole dimension has a frame with .004 MMC, A, B MMC and C MMC. Can a frame contain the datum that it is controlling? If so how does this funcion?





RE: using a datum and within datum frame using same datum MMC
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: using a datum and within datum frame using same datum MMC
If I understand C mmc could/should be removed from frame? Eliminate confusion?
RE: using a datum and within datum frame using same datum MMC
A feature control frame can reference the considered feature, if it is part of a multiple datum feature.
Does the feature control frame look like this:
POS|Dia .004(M)| A | B(M) | C(M) | (B is secondary and C is tertiary)
or like this:
POS|Dia .004(M)| A | B(M)-C(M) | (B and C comprise a multiple datum feature)
If the FCF has the first option with the tertiary reference to C, then the C reference is "self-referencing" and should be removed.
If the FCF has the second option with the multiple datum feature, then removing the C reference will change the meaning.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: using a datum and within datum frame using same datum MMC
Thank you. Feature is called out as your first option defines.
RE: using a datum and within datum frame using same datum MMC
You said: "A feature control frame can reference the considered feature, if it is part of a multiple datum feature."
Is this, in your opinion, always true?
RE: using a datum and within datum frame using same datum MMC
I guess the standard reply in these cases is to ask for you to post a sketch, but I think the gist of the question has been answered: They shouldn't have included C. Yank it.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: using a datum and within datum frame using same datum MMC
You tend to ask these questions that seem simple but really are not. Keep it up!
I wouldn't say that it's always true that a FCF can always reference the considered feature as part of a multiple datum feature. In fact, I really don't like the practice but I mentioned it because the standard allows it and it seems to be commonly used.
I've mentioned this in many other threads that discussed runout FCF's for A and B both referencing A-B. To me this is conceptually flawed - the FCF's ideally should not reference any datum features and have the "datum axis" be arbitrary (as is done for Position tolerances that control coaxiality).
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: using a datum and within datum frame using same datum MMC
I would just like to have clear understanding of first part of your reply, therefore allow me to ask differently.
I took your "A feature control frame can reference the considered feature, if it is part of a multiple datum feature" more or less as "When a FCF applied to a feature references the considered feature in a non-multiple-datum-feature way, this is always invalid callout". Did I read the message correctly?
RE: using a datum and within datum frame using same datum MMC
Tunalover
RE: using a datum and within datum frame using same datum MMC
A picture would clarify the situation.