This paper describes the development and application of a geometric dimensi
on and tolerance (GD&T) model for use in both design and process planning.
The model meets criteria for computability and compatibility with the Y14.5
M standard. The model is first used to capture the designers GD&T scheme on
a feature based design model, validate its completeness, and then transfer
the GD&T to machining features extracted automatically by feature recognit
ion. The model is based on relative degrees of freedom of geometric entitie
s: feature axes, edges, faces and features-of-size. Dimension graphs are cr
eated based on the degrees of freedom for each control direction. Datum ref
erence frames and standard tolerance classes are incorporated into the grap
h. The model allows dimension specification, dimension scheme modification,
and dimension scheme validation. A methodology to automatically determine
the GD&T of machining volumes obtained by feature recognition is also descr
ibed.