Measurement of Basic Dimension

[BalajiPG]

Hi,

We have came across Basic Dimension in the drawing. We know there is no tolerance applicable for the Basic Dimension. But we dont know, Is the Basic Dimension to be captured in the dimension report of PPAP, to see what actual sample value is....

 

[JNieman]

I am unaware of anything written in stone that says yea/nay on the requirement. The majority of customers ask that their values be reported as a reference only, since the True Pos is the true tolerance value that dictates pass/fail. There is no way to assign a pass/fail to a basic XYZ coordinate which has a diametric or spherical tolerance zone, as all ordinate values can be good or bad depending on the value of the others. It's almost a Shrodinger inspection result.

Some customers of mine ask that only the FCF value be reported, some want basic dims in addition, and one particular customer requires even REFERENCE dimensions be documented for, I suppose, additional reference.

I'm following along to see if someone points out a black/white situation in case I can change a customers mind some day.

 

[3DDave]

One can't determine process stability from position variation, so it's useful to report either the raw values or the delta-x, delta-y, delta-z (as applicable) along with the computed variation.

The raw values will be weird if the dimensions are chained or non-existant (as in a centerplane.) The distance is from the datum so the measurement is from the datum, so there may be no dimension on the drawing that reflects that distance.