Profile Control

A profile is the outline of an object in a given plane (two-dimensional figure). Profiles are formed by projecting a three-dimensional figure onto a plane or by taking cross sections through the figure. The elements of a profile are straight lines, arcs, and other curved lines. If the drawing specifies individual tolerances for the elements or points of a profile, these elements or points must be individually verified. Such a procedure may be impracticable in certain cases, particularly where accuracy of the entire profile, rather than elements of a profile, is a design requirement. With profile tolcrancing. the true profile may be defined by basic radii, basic angular dimensions, basic coordinate dimensions, basic size dimensions. undimensioned drawings, or formulas.

6.5.1 Profila Tolerancing. The profile tolerance specifics a uniform boundary along the true profile within which the elements of the surface must lie. It is used to control form or combinations of size, form, orientation, and location. Where used as a refinement of size, the profile tolerance must be contained within the size limits. Profile tolerances are specified as follows.

(a) An appropriate view or section is drawn showing the desired basic profile

(b) Depending on design requirements, the tolerance may be divided bilaterally to both sides of the true profile or applied unilaterally to either side of the true profile. Where an equally disposed bilateral tolcrance is intended, it is necessary to show only the feature control frame with a leader directed to the surface. For an unequally disposed or a unilateral tolerance, phantom lines are drawn parallel to the true profile to indicate the tolerance zone boundary. One end of a dimension line is extended to the feature control frame. The phantom line should extend only a sufficient distance to make its application clear. See Fig. 6-11.

(c) Where a profile tolerance applies all around the profile of a part, the symbol used to designate "all around" is placed on the leader from the feature control frame. See Fig. 6-12. Where segments of a profile have different tolerances, the extent of each profile tolerance may be indicated by the use of reference letters to identify the extremities or limits of each requirement Sec Fig. 6-13. Similarly, if some segments of the profile arc controlled by a profile tolerance and other segments by individually toler-anccd dimensions, the extent of the profile tolerance must be indicated. See Fig. 6-14.

6.5.2 Tolerance Zone. A profile tolerance may be applied to an entire surface or to individual pro-

Unilateral Profile ToleranceProfile Tolerance

(a) Bilateral tolerance

Actual profile

True profile relative to datum A

True profile relative to datum A

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