Simultaneous Requirements

[[Ja...]]

Starting to use the new GD&T engine instead of the classic. So concerning the accompanying callout - Because the callout is basically the same thing as having 8 individual callouts all with the same Datum Reference Frame, do all 8 holes need to be checked simultaneously?

[[Ky...]]

Well, in this case the datum structure seems to be fully constrained right? Simultaneity makes sure that all features in a callout move together rather than separately when there are unconstrained degrees of freedom, but it looks like all of them are constrained in this example.

[[Ma...]]

a fully constrained DRF is not cause to eliminate Simultaneous Requirement.

In ASME Y14.5, the simultaneous requirement applies by default when:

• Multiple features
• Share the same datum reference frame
• And are controlled by separate feature control frames, can be a different set of holes but lie on the same plane but share the same datums and datum order.
• Without an explicit modifier that breaks simultaneity as in Separate Requirement.

 

[[Ja...]]

That's how I was interpreting it as well, however I didn't see anything in the standard that says the features have to be on the same plane. That would be great as it would cut down on programming time a little. What section is that listed in so I can protect my behind if need be?

[[Ma...]]

I just looked and they don’t need to be on the same plane. 
 

ASME Y14.5 requires only that features reference the same datum reference frame—not that they lie on the same plane—for the simultaneous requirement to apply (Section 7.19).

“A simultaneous requirement applies to position and profile tolerances that are located by basic dimensions related to common datum features referenced in the same order of precedence at the same boundary conditions. In a simultaneous requirement, there is no translation or rotation between the datum reference frames of the included geometric tolerances, thus creating a single pattern. Figures 7-46 and 7-47 show examples of simultaneous requirements. If such an interrelationship is not required, a notation such as SEP REQT should be placed adjacent to each applicable feature control frame. … This principle does not apply to the lower segments of composite feature control frames. … If a simultaneous requirement is desired for the lower segments of two or more composite feature control frames, a notation such as SIM REQT shall be placed adjacent to each applicable lower segment … Simultaneous requirements are not applicable and cannot be invoked by notation on single-segment or multiple-segment feature control frames when the datum references are different, the datum references appear in a different order of precedence, or the applicable material boundaries are different.”