is called Datum Reference Frame whereas in mathematics it is the Cartesian
coordinate system invented by Rene Descartes in France (1596-1650). Often one would express
this concept as The DRF is probably the most important concept of GD&T. In order to manufacture and/or
inspect a part to a drawing , the three (3) plane concept is necessary. Three (3) mutually
perpendicular (exactly 90° to each other) and perfect planes need to be created to measure
from. In GD&T this the need to establish the X,Y, and Z coordinates. The DRF is created by so-called
Datum Simulators which are the manufacturing, processing, and inspection equipment such as
surface plate, a collet, a three jaw chuck, a gage pin, etc. The DRF simulators provide the origin
of dimensional relationships. They contact the features (named Datum Features) which of course
are not perfect hence measurements from simulators (which are nearly perfect) provides accurate
values and they stabilize the part so that when the manufacturer inspects the part and the
customer inspects the part they both get the same answer. Also if the part is contacted during the
initial manufacturing setup in the same manner as when it is inspected, a “layout” for assuring
machining stock is not required. The final result (assuming the processing equipment is suitable
for the tolerancing specified) will be positive.