In this paper, locating error effects are analyzed on geometric errors produced in machining processes, such as the parallelism, perpendicularity, and angularity of machining plane or hole surfaces. Inaccurate placement of locator positions in a fixture design may cause a change of workpiece position and orientation, and in turn, contribute to the geometric error of the products. This effect could be complex even if only the variation of one locator’s position is considered because relative slip motions between the workpiece and locators are usually allowed in fixture design. In this research, locating reference planes are established according to the positions of locators. When the locators’ positions change, the variation of these planes can be estimated. The coordinates of an arbitrary point on a machining surface of the workpiece can be determined relative to these reference planes. The coordinate variations of the points on the machining surface can be identified based on the change of locators’ positions, which is used for estimating the geometric errors produced in a machining process due to the inaccuracy of locators’ positions. This information is utilized in computer-aided fixture design and verification.

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