Composite Position of bore pattern - ASME

[[Br...]]

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Both rotation and translation should be enabled on both, but when reporting the top tier, make sure MMC is enabled on the datum feature so that it will still constrain those 2 degrees of translation within the allowable material boundary. And like I mentioned earlier, if there are any other position or profile tolerances, then the top tier has a simultaneous requirement.

[[Ja...]]

[[Me...]]

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That's incorrect. Nothing in that diagram says otherwise. That diagram isn't addressing datum mobility.

[[An...]]

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So true!

[[Aa...]]

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Which diagram? Jay referenced a section and two figures. That brings up a good point. It's dangerous to think that one figure will give you a complete picture of how the standard works. If you just look at the figures and don't bother with the actual text, you will be confused.

[[Me...]]

His statement is false. He provided some diagrams and a section I'm assuming to bolster that statement. They don't. That's all I'm saying.

If MMB has no effect on the position calculation then why is it there on Datum -B- and allowed? The wording in the red boxes doesn't contradict what I'm saying. The geometry is constrained relative to each other and the DRF. The DRF shows MMB on the datum, so that is allowed to best fit depending on the material condition.

[[Aa...]]

In Y14.5, the FRTZF allows for complete translational mobility, and that is exactly what second part of that figure illustrates.

This is from 2009, and I assume they did not change it for 2018.

[[Me...]]

I'm addressing datum mobility and MMB per his statement. Nothing more.

[[Aa...]]

Indeed. But datum mobility typically becomes a moot point when the tolerance zones are only constrained rotationally to the DRF.

[[An...]]

I remember very well the one and only High-Performer of this Forum:

Mark Foster
(learned a lot of him)

Would like to know his opinion to this topic,but I feel that he is gone.

See attached.

Pic_7-27_1.pdf

[[Br...]]

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What Jay is trying to say is that there is no datum shift in the PLTZF because the it says the rotation and translation are constrained by the DRF. What Robert is saying is that it doesn't mention datum shift. Basically, just because datum feature shift/displacement is allowed, doesn't mean those degrees of freedom are not constrained by that datum feature simulator. It is the Datum feature simulator that constrains the degrees of freedom, or more accurately (as described in 2018) the True Geometric Counterpart. Y14.5-2018 para 7.11.12 states: The datum feature shift/displacement shall always be limited or constrained by the true geometric counterpart. The toleranced feature doesn't have complete freedom from Datums referenced at MMB. There are still constraints in place. The true geometric counterpart essentially is the MMB boundary.

[[An...]]

From patterns and frameworks.
See attached.

Pic_7-40_c.pdf

[[Ja...]]

I have created a theoretical features to test how composite tolerance works.
I came to know that, to allow datum shift, both rotation and translation should be selected as everyone said in this discussion and Best fit method should be "View Tolerance (With LMC/MMC of the reference)".

[[To...]]

Ryan Stauffer once posted that Calypso would not show a datum shift unless it was needed. If it passed position based just on the tolerance, no datum shift would be present.