A review of literature indicated that the technique that has found general usage and widespread acceptance for the measurement of surface roughness is the use of a profilometer. This instrument has been found to have at least two limitations in measuring surface roughness. First, there is the limitation associated with the radius of the stylus that prevents an accurate profiling of the surface. Second, the instrument tends to distort the real nature of the image of the solid surface because the vertical magnification is greater than the horizontal magnification. Because of these limitations, substantial research has been reported in the literature on optical techniques to replace the profilometer. The main objective of this study was to compare the profilometer results with the results of a surface roughness measuring technique using speckle contrast in the facing of medium carbon steel. The variables whose effect on the resulting surface roughness was investigated were: the cutting speed, the feed rate, the depth of cut and the surface speed per minute. Two different measures of the resulting speckle contrast were used. First the surface roughness was characterized by the arithmetic average of the speckle intensity, resulting from translating the rough sample across a (He-Ne) laser beam. Second, the surface roughness was characterized at each of twenty randomly selected points; across one of its major diameters, by the resulting speckle intensity. The results indicated that neither the profilometer nor the average speckle contrast were adequate techniques to measure surface roughness in the facing of medium carbon steel. The results also indicated that the point-by-point method of characterizing surface roughness using speckle contrast, is a useful method in determining the effects of the machining variables on surface roughness in the facing of medium carbon steel. The study also pointed out the need for developing a better method of measuring surface finish than the profilometer technique
