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Extend the Form Control with the Continuous Feature Symbol
(In accordance with the ASME Y14.5-2009 standard)

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The continuous feature symbol was added to the ASME Y14.5-2009 standard. Before the addition of this symbol, we didn’t have a good way to apply a form control to a feature of size with interruptions. Some people tried to accomplish this using profile of a surface. The problem was that using profile of a surface on a toleranced feature was not clearly supported in the Standard. The continuous feature symbol is "used to identify a group of two or more features of size where there is a requirement that they be treated geometrically as a single feature of size."

On this spool drawing the CF symbol has been added to the Ø40±0.05 dimension. There are actually 5 diameters that this dimension applies to. Without the CF symbol there would have to be "5X" before the diameter symbol and the cylindricity tolerance would apply to the five diameters individually. The function of this spool requires that the 5 diameters act as one diameter. Selective assembly is used to assure a metal on metal seal. The size of the diameters may vary more than the form. The form (cylindricity) of the features acting as a single feature is critical.

Prior to the 2009 revision of the Standard there was not a well defined way to accomplish this.

Back to Tips Tip added Nov 2011