GD&T Position

[[Ji...]]

Dear colleagues, in the previous method of evaluating the position tolerance of a hole pattern, modifying the tolerance did not affect the measurement results. However, in the new GD&T evaluation of hole pattern position tolerance, updating the tolerance zone also changes the measurement results. What is the reason for this? What is the difference between the two?

[[A...]]

Morning!

Looking at this, the Pos Tol in the left photo is adjusting the tolerance individually with an allowed Best Fit (Rotational). Calypso looks at the individual tolerances and finds the best position to rotate all features.

The main Element that has the most bearing on your rotation is B.1 where the tolerance band is relatively small vs B.4 where you have a much larger tolerance band. Calypso may rotate your elements to try fit B.1 into tolerance even if the element B.4 has to rotate away from its own tolerance center.

When you establish a tolerance on the right photo, that tolerance applies to all elements and so B.1 thru B.4 will all be treated equally.

[[Ji...]]

 

My understanding is this:
In the old hole pattern evaluation method, the best-fit position was calculated based on the nominal values. As a result, the size of the tolerance zone had no influence on the measurement result.

The new GD&T feature, however, seems to calculate the best-fit position based on the tolerance zone size of each individual feature.

This is just my personal understanding. Is there any official documentation or explanation available for the new GD&T functionality?

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[[A...]]

I'm sorry, I've only explained Tolerance Best Fit, this is my default and is not everyone's.

You have 4 Best Fit options
 

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With this, I still expect some change to rotation if you are allowing a larger tolerance zone then maybe you do not need additional rotation. Maybe compare the two rotation angle actuals and see how much it changes from one tol-zone to the larger.