Evaluation of straightness and flatness tolerances using the minimum zone

This paper presents an algorithm that can be used to determine if sample measurements from a coordinate measuring machine, or other two- or three-dimensional measuring device, meet the ANSI Y14.5M requirements for straightness or flatness. The procedure utilizes the concept of a convex hull to give the minimum tolerance zone from a set of measured points. To date, approximation methods or iterative search techniques have been primarily utilized for determining the minimum zone, but these methods do not necessarily provide the absolute minimum zone. This paper presents a method that guarantees the minimum zone, Examples are presented which compare the minimum zone method developed with the least-squares evaluation method.