In this study, we have investigated the effects of different insert radii of cutting tools, different depths of cut and, different feed rates on the surface quality of the workpieces depending on various processing parameters. Properly, the AISI 1030 steel is processed at a digitally controlled computerised numerical control(CNC) turning lathe without using cooling water with three different insert radii (0.4, 0.8, and 1.2 mm) of cemented carbide cutting tools, coated with three layer coating materials (outermost is TiN) applied by the chemical vapour deposition CVD technique. The effects of five different depths of cut (0.5, 1, 1.5, 2, 2.5 mm) and five different feed rates/advancing steps (0.15 0.2 0.25 0.30, 0.35 mm/rev) on the surface roughness values have been investigated by a turning process while from the cutting parameters the cutting speed is kept constant at (300 m/min). It is seen that the insert radius, feed rate, and depth of cut have different effects on the surface roughness. In the experiments, the minimum average surface roughness has been obtained using the cutting tools of maximum insert radius (1.2 mm). The surface roughness have been improved by 293% when the insert radius (0.4 mm) was increased by 200% (1.2 min). When the feed rate (0.35 mm/rev) was reduced by 133% (0.15 mm/rev), the surface roughness have been improved by 313%, and by reducing the depth of cut (0.5 mm) by 400% (0.25 mm), an amelioration of 23% has been obtained on the surface roughness. (c) 2005 Elsevier Ltd. All rights reserved.