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Simultaneous Requirements

• Simultaneous Requirements means that the requirements apply at the same time
• Simultaneous Requirements are gaged in the same gage at the same time
• Simultaneous Requirements apply to Tolerance of Position and Profile
• Requirements are simultaneous when they locate the features
  To the same datums
  In the same order
  At the same material condition
• Simultaneous Requirements can be over ridden by the note:  “Separate Requirement”
  

  
 
 

  
  

No two of the Feature Control Frames above have the same datums in the same order and at the same material condition.  So none of them are simultaneous requirements.

   
  

   
 

Now the two Feature Control Frames shaded yellow are simultaneous requirements with each other because they have the same datums in the same order and at the same material condition.   The two Feature Control Frames shaded light green are also simultaneous requirements with each other because they have the same datums in the same order and at the same material condition.

   
  

  
  

The separate requirement notes turn all of our simultaneous requirements into separate requirements.  Note that for each set of simultaneous requirements, it was only necessary to put the note under one of them. Once one of the Feature Control Frames is a separate requirement, the other one is left as a separate requirement by default.



Simultaneous Requirements in a tolerance stack:

When a tolerance stack is done between two features that are simultaneous requirements, there is no datum feature shift between the features that are simultaneous requirements.

Datum feature shift is an extra amount of location tolerance that is allowed between the datum and the features that are located relative to the datum.  So datum feature shift really means that the datum and the considered features can be closer to each other or father away from each other than they could without datum feature shift.

   
   
 

    

Consider the housing above.  Datum [B] is the axis of the large opening.  The datum feature shift allows the considered features (the threaded holes) to move an additional amount relative to the datum.

    
  

In the figure above, the considered features are moved as allowed by datum feature shift.  Note that the location of each hole is affected relative to the datum.  However, the location of each considered feature relative to the other considered feature is not affected.