Use Extensions of Principle—When You Need To
Don’t be surprised if you do not find your parts in the Y14.5 standard. The Standard is a collection of building blocks. There are an infinite number of w ays to combine these building blocks to control your parts and still be in compliance.
The standard does not specifically show how to tolerance parts such as preformed hoses or bent tubes and rods. However, the building blocks needed to control such parts are in the Standard. Here is a drawing of a preformed tube. Datum features A, B and C have established origins of measurement. The datum features are all controlled. Datum feature A is a feature of size. Datum feature B is positioned relative to the datum axis established by A. Datum feature C is held perpendicular to datum axis A. The rest of the hose needs to be located. This could have been done using profile of a surface but the drawing shows a different option. The size is refined as LOCAL SIZE so Rule #1 does not apply. The position tolerance is applied to EACH ELEMENT. In other words, the position tolerance follows the basic dimensions along the center of the tube between S and T one slice at a time.
Although this approach is not shown, specifically, in the Standard, the building blocks are there. This drawing will have one clear meaning to anyone who knows and understands the Standard.
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