The surface controlled must lie entirely within the space between the two planes. The other lies at the deepest trough of any irregularity of the surface. One lies at the peak of the tallest irregularity in the surface. The Tolerance Zone for a Flatness Tolerance is based on two parallel planes. It controls how much a surface on a part may deviate from an ideal plane. Flatness is a form control, because it is used to control the form or shape of a feature. It is not dependent on any other datums or features. The GD&T Flatness symbol references how flat a surface is. GD&T Flatness Symbol Definition of Flatness If the flatness tolerance had been 0.6, it would result in a condition where the overall size of the part may have exceeded its allowable size limits.īecause flatness refines a surface, it may be used in a tolerance stack.Easy Guide to GD&T: Flatness Note that the flatness tolerance must be less than the size tolerance associated with the surface. The boxed symbols can be read “this surface must lie between two parallel planes spaced 0.2 apart in all views.” The right figure shows a possible actual part condition. The left figure shows the drawing callout. Flatness tolerance applies in all drawing views, not just the view showing the tolerance callout.Īn example of flatness is shown below. Flatness is usually used on a surface associated with a size dimension, acting as a refinement to the size requirement to ensure proper function of a part, or to promote even wear. Since flatness is applied to an individual surface, this tolerance does not need to be related to a datum. In GD&T flatness tolerance defines a zone between two parallel planes within which a surface must lie. Many part designs contain surfaces that need to be uniform.
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