files taken at various cross sections through the part. These two cases are provided for as follows.
(a) Profile of a Surface. The tolerance zone established by the profile of a surface tolerance is three-dimensional, extending along the length and width (or circumference) of the considered feature or features. This may be applied to parts having a constant cross section as in Fig. 6-12, to parts having a surface of revolution, or to parts (such as castings) defined by profile tolerances applying "ALL OVER" as indicated below the feature control frame.
(b) Profile of a Line. The tolerance zone established by the profile of a line tolerance is two-dimensional, extending along the length of the considered feature. This applies to the profiles of parts having a varying cross section, such as the tapered wing of an aircraft, or to random cross sections of parts as in Fig. 6-18, where it is not desired to control the entire surface of the feature as a single entity.
6.5.3 Explanation of Profile Tolerance. The tolerance value represents the distance between two boundaries equally or unequally disposed about the true profile or entirely disposed on one side of the true profile. Profile tolerances apply normal (perpendicular) to the true profile at all points along the profile. The boundaries of the tolerance zone follow the geometric shape of the true profile. The actual surface or line element must be within the specified tolerance zone, and all variations from the true profile must blend. Where a profile tolerance encompasses a sharp corner, the tolerance zone extends to the intersection of the boundary lines. See Fig. 6-15. Since the intersecting surfaces may lie anywhere within the converging zone, the actual part contour could conceivably be rounded. If this is undesirable, the drawing must indicate the design requirements, such as by specifying the maximum radius. See Fig. 6-12.
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