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using a datum and within datum frame using same datum MMC 1
- Thread starter Harol
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Harol,
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.
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.
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- #5
Proper credit to Evan 
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
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
pmarc,
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.
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.
pmarc
Mechanical
- Sep 2, 2008
- 3,248
Evan,
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?
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?
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