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How to measure a Critical Characteristic that is a Basic Dimension


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We have a part that we are looking at and there is one dimension that is a Basic Dimension, which they have also marked as a Critical Dimension. The basic is used for a Profile of .010" so would the Critical Dimension be the Profile reading, or the actual of the Basic dimension? Capture.JPG


A Sea of Statistics
Basic Dimension = "A Numerical value used to describe the Theoretically Exact Size, True Profile, Orientation, or Location of a Part Feature or Datum Target." Likely it is the "Profile of a Surface", that is it is in fact based or established by virtue of the Basic Dimensions...
By definition, a reference dimension is ALWAYS exactly correct (i.e. 1.020 in this case). However, what your customer MAY be looking for is the deviation of the profile in one direction (for example, (presuming it is a bilateral callout) it may be more advantageous to have the profile towards the low side, rather than to the high side. Best idea is to contact your customer, and determine what it is that they are actually trying to control.

Cari Spears

Super Moderator
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Super Moderator
The feature control frame does make it clear what they're trying to control. Unless there is a description of the unequally distributed tolerance, it means that the tolerance zone is equally distributed.
I don't disagree Cari - the print callout is very specific. However, what the print says and what the customer WANTS (or is concerned with) may be two completely different things.
As I suggested, it is easiest to discuss with the customer up front, so that everyone is on the same page.
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