understanding minimum material envelope and mating envelope on practice exam questions for GDTP preperation

[DM888]

I'm having an issue understanding the answers to the following questions. They're from a practice exam for the GD&T senior certification.

1) A tolerance of position or orientation is totally dependent on the size of unrelated actual minimum material envelope of the considered feature when the tolerance is
a) basic, b) zero at lmc, c) next to the size dimension, d) zero at mmc

2) A tolerance of position or orientation is totally dependent on the size of unrelated actual mating envelope of the considered feature when the tolerance is
a) basic, b) zero at lmc, c) next to the size dimension, d) zero at mmc.

The part that is confusing me is the use of minimum material envelope and mating envelope. I may not have a good understanding of their definition and how they apply to zero at mmc/lmc cases.

Thanks,

Dan

 

[3DDave]

Sometimes at the school for the gifted a student is pushing on the door labeled PULL. It takes a while for the realization to sink in.

I think you have this now. Congrats and best of luck if you are going to take the exam.

 

[Burunduk]

Interestingly, while the "bonus" for a tolerance at LMC depends on the size of the unrelated actual minimum material envelope, the axis being controlled is still the axis of the unrelated actual mating envelope:

" 5.9.6.2 Explanation of the Axis Method. When an orientation or position tolerance is applied on an LMC basis, the feature’s axis, center plane, or center point shall not violate the tolerance zone. The tolerance avail-
able is the specified value if the unrelated actual minimum material envelope is at the LMC limit of size. When the size of the unrelated actual minimum material envelope of the feature departs from LMC, the tolerance zone increases. "

And in the definitions section:

" 3.32 FEATURE AXIS
feature axis: the axis of the unrelated AME of a feature.

3.33 FEATURE, CENTER PLANE OF
feature, center plane of: the center plane of the unrelated AME of a feature. "

 

[greenimi]

Interestingly, while the "bonus" for a tolerance at LMC depends on the size of the unrelated actual minimum material envelope, the axis being controlled is still the axis of the unrelated actual mating envelope:

" 5.9.6.2 Explanation of the Axis Method. When an orientation or position tolerance is applied on an LMC basis, the feature’s axis, center plane, or center point shall not violate the tolerance zone. The tolerance avail-
able is the specified value if the unrelated actual minimum material envelope is at the LMC limit of size. When the size of the unrelated actual minimum material envelope of the feature departs from LMC, the tolerance zone increases. "

And in the definitions section:

" 3.32 FEATURE AXIS
feature axis: the axis of the unrelated AME of a feature.

3.33 FEATURE, CENTER PLANE OF
feature, center plane of: the center plane of the unrelated AME of a feature. "

And you also can see that the rule#1 is reversed for the LMC callouts versus the MMC ones.
MMC: perfect form at MMC is required.
LMC: perfect form at LMC is required.