MMC on a Surface

[jjslife]

i have a situation i am trying to resolve. my blue print has a callout of a diameter true position rel to -C- and -B-. both of them are surfaces and the geometrical feature control has a modifier for MMC on both datums. they are outside surfaces, so would i get more tolerance with the surfaces being smaller or larger ???
thanks
JJ

 

[pmarc]

Isn't it the same issue you asked about in the following thread?:

http://www.eng-tips.com/viewthread.cfm?qid=301025&page=1

 

[jjslife]

yeah, but i don't know how to apply the tolerance
thanks

 

[pmarc]

A sketch or more detailed description of the blueprint would really help. Without it it is really hard to say whether the callout is legal or not. According to which dimensioning standard is the drawing?

 

[jjslife]

this is the scoop guys.... i can not get my hands on a copy of anme y14 at the moment. the drawings states interpretation per asme y14.5m-1994
any help would be grateful

 

[pmarc]

If the drawing follows ASME Y14.5M-1994 then I would say such callout is illegal.

Application of (M) or (L) modifiers on datum features that are surfaces was introduced only in Y14.5-2009. Are you sure that location of datum feature symbols is indicating surface elements as datum features and not features of size for instance?

 

[fsincox]

I am with pmarc, material modifiers on surface datum features was not defined in the 1994 standard and may have been actually prohibited.
Frank