REAL life example of LMC use.
REAL life example of LMC use.
(OP)
Hello
I read and I understand the LMC and MMC. I can think of a dozen example of where I could use MMC but none of when LMC could become useful: having bonus when you have more material??? Can you give me a real life example please? I doubt that it is a theoretical concept.
I read and I understand the LMC and MMC. I can think of a dozen example of where I could use MMC but none of when LMC could become useful: having bonus when you have more material??? Can you give me a real life example please? I doubt that it is a theoretical concept.





RE: REAL life example of LMC use.
“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV
RE: REAL life example of LMC use.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: REAL life example of LMC use.
A similar instance I recently used it for was the position of a feature when a related datum width is at LMC i.e. the larger the datum feature becomes the less critical that the subfeature is centered relative to the datum. This was combined with a MMC callout on the subfeature such that there is 0 positional tolerance when both the datum is at LMC and the subfeature is at MMC.
RE: REAL life example of LMC use.
All my exaample where considering assembly. now it makes better sens.
thanks.
RE: REAL life example of LMC use.
I drew up a casting with a hole that had to be bored out. On the casting drawing, I specified the positional tolerance at LMC to ensure that there would be material available for the subsequent, accurate machining.
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JHG
RE: REAL life example of LMC use.
RE: REAL life example of LMC use.
- Holes that are fitted with alignment spring pins. Since the width of the spring pin is narrower with a smaller fastening hole, there will be more clearance and therefore a greater positional tolerance with the mating alignment hole.
- Shaft-to-bore sealing grooves for ring seals. In the case of a groove on a shaft (piston seal) the size of the shaft and groove diameters are controlled, as is their coaxiality to ensure a suitably even squeeze around the seal circumference. The LMC would be the case where there is the least amount of overall squeeze on the seal with the shaft inserted in a bore, so coaxiality is more important. (I think this is a more dubious example, however; I've never seen it in reality. I guess this is because in most situations the groove is cut on the same axis of the shaft, where coaxiality deviations are too small to be worth considering, and grooves tend to be sized to provide ample squeeze for any reasonable amount of eccentricity anyway).
RE: REAL life example of LMC use.
2. LMC concept can also be used in assemblies when press-fit between features located from their datum(s) is always required. Again, the concept controls size of innner boundary of pin and outer boundary of hole. If IB of pin is greater than OB of hole the press fit requirement is met.
RE: REAL life example of LMC use.
Think of an engine head gasket... the cooling and lubrication holes in the block and head that pass fluids through the gasket as well as those gasket holes should have their tightest constraint functionally at LMC... while the head bolt holes and perhaps the dowel pattern spread should have their tightest constraint functionally at MMC.
RE: REAL life example of LMC use.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?