composite tolerance at lmc : is it nonsense?

[supergee]

I was trying to think of a practical use of LMC when I realised that, though it is not forbiden in ASME y14.5 2018... it doesn't seem to make sense... at least with a patter of holes. The LMC enable one to have bonus tolerancing when material departs from LMC. one cannot increase that bonus further. am I right to understand that?? here is an example. (please disregard that the holes are threaded... it's beside the point here) the only thing that would make sense, if allowable, is a multisgment positionnal tolerance right?

 

[3DDave]

Typically (L) would be applied to bosses or other external features. Unfortunately there is no hard gauging element that can interact with an LMC boundary.

 

[3DDave]

There is one weird case for LMC on a hole. Picture an oil drain port. You want to ensure that the largest hole never exceeds the matching hole in the gasket and vice versa. The smaller the hole the more the hole can wander around and the oil will remain constrained to the confines of the LMC.

 

[Wuzhee]

Our Compressor department frequently uses LMC on cast aluminium parts where minimum wall thicknesses are needed. Other than that, I don't know much practical use for LMC. Can't gauge it, hard to comprehend to most engineers. It wasn't even taught in our school too.

Btw I see "Composite" in the title, but there aren't any on the drawing. You meant "Position" right?

 

[Burunduk]

I am not sure about what exactly doesn't make sense.
Does it not make sense functionally or from some other reason?
"The LMC enable one to have bonus tolerancing when material departs from LMC. " - yes.
"one cannot increase that bonus further." - further after what?
I'd say there is rarely a reason to give a location bonus as the hole gets smaller but there are some situations. The one being mentioned mostly is the function of preserving wall thickness.
Note that in a pattern, the bonus (adjustment of the size of the tolerance zone per the feature's actual size) applies to each feature individually.

An unrelated point - I would not associate a profile feature control frame with a size dimension the way you did. If the intent is to control the width of datum feature E by profile, make .250 basic, separate the profile FCF from the dimension, place 2X above the FCF, and extend two leaders from it. What you show may look cleaner, but with few exeptions associating an FCF with a size dimension without any leaders to surfaces, implies a control of a theoretical center.