Minimum radius method for measuring curved edges on a coordinate measuring machine

When measuring an edge on coordinate measuring machines, the radius of the stylus is hundreds of times the size of the edge. A small angular error in the corrected measured point results in a significant error in an edge radius. In this paper, a Minimum Radius (MR) method for stylus radius correction is proposed. Distinguishing from the standard method that uses surface normals, MR is based on simple geometric relationships and the minimum radius principle. The verification of the needle artifact demonstrates a deviation of the average radius of 3.8 % with the results of the video measuring microscope. The average radius is 0.0561 mm and the standard uncertainty is 0.0005 mm. The MR method was also experimentally verified in measuring the edges of compressor blade and end mill. The advantages of the MR method make it suitable for measuring edges with unknown center coordinates and radius.