Composite Tolerance Modifier Change

[fsincox]

Is it legal to use a ,say, MMC modifier in the upper portion of a composite tolerance and a RFS in the lower section of the TOLERANCE section. I know the Datum modifiers can not change per ASME. What say you all, or is there a statement in the standards on it?
Thanks,
Frank

 

[axym]

Frank,

It doesn't say that you can't, so therefore it must be okay ;^).

That's actually a good question. I would say that it should be legal - I can't think of a reason why this should not be allowed.

Your question brings up another issue as well. I looked through the composite position examples in Y14.5-2009, and the MMC modifier is used in all of them. There are no composite position examples in which the features are referenced RFS. Does this mean that it's not legal?

The entire position section is very heavily weighted to MMC applications. The only figures with position RFS are 7-5, 7-29, 7-35, and 7-65. I believe that there are more figures with LMC than RFS.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[mkcski]

fsincox:

https://www.eng-tips.com/

I am wrestling with the design requirement that would want RFS in the lower frame - got an example?

Certified Sr. GD&T Professional

 

[fsincox]

I do not want to get caught up in advocating for it, I just want a check with others who may remember a particular passage in the standard I have forgotten. The application is (2) dowel pins, so I agree with the RFS as the final tolerance (lower). I believe the upper was just trying to say it is not as important to the outside datums in a cheap/easy way other than stating another separate tolerance line which many people did not realize their could be more than (2) lines in the old days. It kind of makes me think it would have made more sense to use LMC, smaller hole has more room to move?
Frank

 

[mkcski]

Thanks.

Certified Sr. GD&T Professional