Finish on surface ground steel

Abstract

The argument between production and inspection or supplier and purchaser regarding surface finishes on machined parts often is not very easily resolved. Surface finishes will vary from one spot to another even if taken in the same direction relative to machining marks. A change in direction of the stylus of the measuring instruments in relation to tool marks on the surface will give different readings and, within limits, could cover almost any particular surface finish requirements that the specifications may demand. This paper treats several important factors involved and presents an analysis of differences in surface finish, as encountered on a flat ground surface and measured with two types of surface finish measuring instruments. A series of surface grinding tests were carried out under fixed machining conditions in order to determine the relationship between surface finish and table feed for two kinds of steel. Results are given in the form of diagrams with profilometer readings plotted against table feed. The existence of maximum and minimum surface finish reading directions at any point of the testpiece surface is pointed out, as well as the orientation of these preferential directions, assuming as a reference the local direction of the tangent to the wheel marks. A short mathematical analysis confirms these assumptions.