The Influence of Measuring Force, Stylus Radius, and Surface Finish on the Accuracy of Measurement of Work-Pieces by a Comparator

Abstract

An investigation is described which was undertaken to determine the effect of the measuring force and stylus radius of the comparator on the measured sizes of work-pieces made of the materials and having the machined finishes commonly used in engineering. The information was required to enable recommendations to be made concerning the performance and certain features of engineers' measuring instruments. The sizes of the work-pieces were measured using styluses of different radii under successively increased measuring forces. It was found that the sizes obtained at any one point were influenced mainly by alterations in the measuring force, and that the effect of the surface finish was relatively small. The relation between the measuring force and the magnitude of the deformation at the contacting surfaces of a solid stylus and a work-piece followed a law similar to that derived by Hertz from theoretical consideration of elastic deformation, despite the appreciable plastic deformation of the work-pieces that occurred in some instances. Variations in the measured sizes over an area of a work-piece were influenced more by the surface texture of the work-piece than by the radius of the stylus used.