JO Engineering
Mechanical
- Oct 29, 2020
- 10
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What if the datum B hole measures on the LMC side, dia. 10.6?B(MMB) is called datum feature shift and is NOT a bonus.
Only the circled M after Ø0.2 is called "bonus" (additional tolerance) and not the circled M after B (which again is datum feature shift)
Datum feature shift is offering additional datum feature mobility (giving back some datum feature mobility)
Do not add the datum feature shift to the "bonus" tolerance because that would be wrong (very wrong).....
ok thanks. I will conclude that adding (M) on datum B does not change anything. B (M) = B.The amount the datum feature can move rarely has a good calculation for the true-position shift. There are some cases that make it appear that way, but that is misleading.
At it's heart, true position is defined relative to the ideal datums; datum shift allows the part to move relative to the datum features, not to allow the holes to move relative to the true position of the holes. The true position of the holes remains fixed. The deviation from that true position is only due to the tolerance in the Feature Control Frame.
There is no sense in adding them and they do not affect each other.