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Consider straightness on your parts made from flat stock - 1994 (#26)

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

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Many parts are made from stock which is left in the as furnished condition. Rule #1 does not apply to the thickness when “STOCK” is specified on the size dimension. Therefore, the form variation of the part is whatever the mill supplies. Many designers will control the form of such parts with flatness applied to one surface. Flatness is often a very time-consuming inspection. When straightness at MMC is applied to the material thickness, a simple envelope gage at the virtual condition may be used to limit form variation. Straightness applied to the size dimension controls the derived median plane [6.4.1.1.3]. In this example, the envelope gage used to verify straightness would measure 1.025. The actual local size of this part must be checked with a micrometer type measurement to assure that, at any cross section, the thickness is between .995 and 1.005.

NOTE: In the 2009 & 2018 Standards the derived median plane of a width is controlled using flatness, not straightness.

This tip is in accordance with ASME Y14.5M-1994.
This tip was originally released in July 1999.

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Back to Tips Tip added Jul 2020