Are There Any Form Tolerances in Precision Parts Processing?

Position tolerance for precision part machining is the actual total change relative to a reference position. Position tolerances are used to limit the difference between the actual position of a measuring element on a mechanical part and its ideal position, which is determined by reference dimensions or theoretically correct dimensions. Like form tolerances, each item of positional tolerance limits the variation of the actual elements of the part within a specific area through positional tolerance bands. Since the concept of tolerance zone is used during processing, the position tolerance zone not only limits the position error of the component under test, but also limits the shape error of the component. Unlike the shape tolerance zone, the position tolerance zone must have a corresponding relationship with the datum. The datum plays the role of orientation and positioning in the position tolerance zone of the element being measured.
Precision parts processing position tolerances can be divided into three categories: orientation tolerance, positioning tolerance and runout tolerance. Orientation tolerance is the amount of variation allowed from a measured actual element to an ideal element in a specific orientation. The orientation of the ideal element is determined by the reference angle and the theoretically correct angle. Orientation tolerance is divided into three items: parallelism, perpendicularity and inclination. Positioning tolerance is the total amount of allowable variation in the measured actual element to the ideal position of the element. The ideal element position depends on the reference values and the theoretically correct size. Positioning tolerances are divided into three parts: positional concentricity and symmetry.
Runout tolerance is the maximum allowable runout when the actual element being measured rotates without axial movement or continuous rotation about a reference axis. The so-called maximum runout refers to the difference between the maximum reading and the minimum reading measured by the indicator in a given direction. Beats are divided into circular beats and complete beats.
Circular runout: refers to the maximum reading difference measured by the indicator in the specified direction when the actual surface being measured rotates around the reference axis without axial movement.
Complete runout: refers to the maximum reading difference measured by the indicator during the entire process when the actual surface being measured rotates around the reference axis without axial movement, and at the same time the indicator moves parallel or perpendicular to the reference axis.
For the machining industry of precision parts processing, the purpose of establishing tolerances is to determine the geometric dimensions of the product and make it vary within a certain range to meet the requirements for interchange and use.