The role of surface roughness is very important in machining processes. The surface finish and tolerances are most critical quality measures in various mechanical products. The main objective of this paper is to find out the effect of machining parameters on a surface roughness in a lathe boring operation in dry condition. This paper shows the study of surface roughness for boring of gray cast iron (250BHN) by using carbide tool under dry condition. The effect of boring parameters (tool nose radius, feed, spindle speed and depth of cut) was analyzed using analysis of variance. These variables were computed using Taguchi’s design of experiments (DOE). The DOE gives the optimal values of speed, feed and depth of cut for tool nose radius of 0.4 and 0.8 mm. The three-factor three-level fractional experiments were conducted. This result shows that the effects of speed, feed, depth of cut and tool nose radius on surface finish are statistically significant. The results observed that using larger tool nose radius always gives a good surface finish. The results also revealed that the following level for each of the factors produces the smooth surface finish within the range of experiments: larger tool nose radius, lower feed, higher speed and lower depth of cut. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.