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Irregular Features
(In accordance with the ASME Y14.5-2009 standard)

PDF of this Tip

Often features are not simple planes, holes and bosses. The next few tips will deal with various means of controlling irregular and complex features. These features should be dimensioned using BASIC dimensions and toleranced for size and form using profile of a surface. Virtually any shape may be defined and controlled in this manner. This type of feature may use either Profile of a Surface or Position to control location and orientation relative to datum references. On the part shown below, a hex shaped hole uses this approach. A composite profile of a surface control is shown. The upper segment controls
the location and orientation of the feature relative to the datum reference frame, where the lower segment does not reference datums and controls the size and form of the feature. This tip will explain the meaning of the upper segment. On the drawing below, the upper segment of the Profile of a Surface callout controls the location and orientation of the hex with respect to the datum reference frame established by A, B, and C. The feature must be located within the 0.4 wide tolerance zone shown below.

The figure shown below is a possible gage that might be used to inspect the 0.4 profile tolerance. The values shown are theoretical design values which do not include gage tolerance and wear allowance.

Our next tip will explain the meaning of the lower segment of the Profile callout.

Back to Tips Tip added Jan 2018