Simultaneous requirements in GD&T - What are they ?
Mufaddal Rasheed 
How to interpret a GD&T drawing with simultaneous, how to identify and differentiate?
What are simultaneous requirements in GD&T ?
Lets take the below example of a GD&T drawing of a plate with three holes.
There are three Feature control frames for tolerance of position
Number 1 and Number 2 frame have the same sequence of datum in them.
This means that they are required to be controlled simultaneously not separately. When the part is inspected, the position for both the holes (15 and 6 ) will be inspected in one instance.
Whereas the 3rd feature control frame will be inspected separately as its datum sequence is not same.
The Simultaneous requirement rule can be overridden by giving a note below the feature control frame as “SEPARATE REQUIREMENT” or “SEP REQT” to make it clear that they would be inspected separately .
How to identify simultaneous requirements?
- Sequence of the datum and datum feature modifiers used have to be identical .
- Applies only to profile and position tolerances
- Control mutual relationships
- Have to be inspected together.
- Keeping simultaneous requirements or separating out depends on Design intent – functional requirements of features
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Geometric Dimensioning & Tolerancing : Advanced concepts
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Categories: : GD & Tolerancing