In the figures below, we are measuring the surface profile of a metal part as it is polished through 4 passes. Fig. 1 indicates the number of polishing passes that have been applied to each corresponding side, with the roughest surface finish having only 1 pass and the smoothest having 4 passes.

Each side was measured on the Profilm3D^® profilometer with a 10x objective at the 4x zoom setting to assess the surface roughness. Fig. 2 shows the surface roughness analysis of the four scans from each side; it is clear to see that the surface roughness is getting smoother with each polishing pass.

To put the changes in surface roughness in numbers we can measure, we can use comprehensive roughness parameters such as Sa and Sq. Plotting the surface roughness versus the number of polishing passes (fig. 3) shows how the surface roughness decreases with increased polishing. The surface roughness decrease slows down with the number of finishes. It is also clear from these data that the fourth polishing pass added only a marginal changes to surface finish.