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Yup, Circularity Error Can Be as Large as the Total Size Tolerance (#178)

(In accordance with Y14.5M-1994 standard)

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Here is a question that comes up from time to time. "How can the circularity error be as large as the total size tolerance since circularity error is a radial tolerance?" The reason is that the LMC and MMC size limits of a feature of size are not coaxial values. The total size tolerance on the inside diameter of 60.71 is 0.06 mm. The figure at the bottom illustrates an extreme case where the hole would just accept a 60.68 (MMC) full form check while at some cross sections the LMC size of 60.74 was not violated. Therefore, size is verified. The circularity error of this particular feature is 0.06, the total size tolerance, since the circularity tolerance zone is comprised of two concentric circles. The size of the circles defining the circularity error could be 60.68 and 60.8 as illustrated. If this isn’t desirable, a circularity tolerance with a value less than 0.6 could be added to refine the circularity control provided by the limits of size. In this case, a 0.025 circularity tolerance was added.

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Back to Tips Tip added Nov 2004