mary datum feature relates the part to the datum reference frame by bringing a minimum of three points on the surface into contact with the first datum plane. See Fig. 4-3(a). The part is further related to the frame by bringing at least two points of the secondary datum feature into contact with the second datum plane. See Fig. 4-3(b). The relationship is completed by bringing at least one point of the tertiary datum feature into contact with the third datum plane. See Fig. 4-3(c). As measurements are made from simulated datum planes, positioning of the part on a datum reference frame in this manner ensures a common basis for measurements.
18.104.22.168 Parts With Inclined Datum Features. For parts with inclined datum features as shown in Fig. 4-4, a true contacting plane is oriented at the basic angle of the feature. The corresponding plane of the datum reference frame is rotated through
Third datum plane
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