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The Tangent Plane Requires a Form Control
(In accordance with Y14.5M-1994 standard)

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Where the tangent plane modifier is applied to a geometric tolerance, it does not provide any form control. In this example, the profile tolerance is modified with the tangent plane symbol. Without the tangent plane symbol, the profile tolerance is controlling the location of the surface to the datum reference frame established by A-B C. It would also control the perpendicularity of the feature to datum axis A-B and flatness within 0.2. Some processes such as casting and molding often result in surfaces with depressions called sink. Where the design can allow for these depressions and still achieve the function, the tangent plane modifier may be used to accept more functional parts. The tangent plane modifier means that the form error, flatness and straightness, of the surface is ignored. Therefore, it is necessary to provide some form control. In this case, a flatness control with a value larger than the profile tolerance would be appropriate. Where the tangent plane modifier is not present, a flatness control would have to be smaller than the profile tolerance.

Back to Tips Tip added Oct 2006