We have a pattern of holes which are located using ordinate dimensions. Their tolerance zones are specified using a position tolerance frame, so the dimensions themselves are basic. I have left the origins (sometimes called the base) of the ordinate dimensions as plain numbers, without a rectangle around them. Another engineer insists that because the dimensions themselves are basic, the origin must be too.
This does not make sense to me, since the point of a basic dimension is to represent the theoretically exact location of a tolerance zone, but the origins (being the reference points from which the dimensions are measured) have no tolerance zones.
The image shows the situation: the upper version is correct in my view, the lower is what my comrade prefers. Which is correct?
Brian,
My interpretations is that you are trying to use two different dimensioning schemes to document the part.
Ordinate Dimensioning utilizes a "0" point and then location dimensions based on the distance from said point
Basic Dimensioning are most commonly accompanied by a positional tolerance on the feature being dimensioned.
Having said this, using your combined dimension scheme there isn't any right/wrong way.
I would choose one or the other.
Just my 2¢
Eddie