## 3 Results and Discussion
With a feed of 0.155 mm/rev and a fixed pass of 0.5 mm, the most influential parameters for achieving the lowest average surface roughness were a spindle speed of 1250 rpm and a cutting-edge angle of 90\({}^{\circ}\). Under these conditions, the Ra value recorded was 2.056 \(\upmu\)m. The data presented in Figure 7 indicated that the average surface roughness decreased as the cutting-edge angle increased. In Figure 8, the sample was machined on a lathe under conditions where the feed was 0.088 mm and the depth of cut was 0.5 mm. The effect of changes in the value of the cutting-edge angle on the surface roughness was investigated. The graph revealed that the smallest average surface roughness value was obtained at a significant cutting-edge angle of 90\({}^{\circ}\) and a spindle speed of 630 rpm. This practical result reassures us that these parameters are indeed the most suitable for achieving the best surface roughness. The largest average surface roughness value was obtained at a significant cutting-edge angle of 70\({}^{\circ}\) and a spindle speed of 480 rpm. The average surface roughness measurement value Ra1 corresponds to the value obtained when operating at n1 spindle speed. Ra2 and Ra3 are similar, respectively. It was observed that the value obtained with n2 in the figure is a more suitable working value in practice than n1 and n3, respectively. For feed of 0.088 mm/rev and 0.5 mm fixed pass values, the working parameters for the most suitable average surface roughness value are 630 rpm spindle speed and a large cutting-edge angle of 90\({}^{\circ}\). Ra value was obtained as 1.667 \(\upmu\)m. In Figure 8, the average surface roughness decreased with increasing values of large cutting-edge angles. Figure 6: Surface roughness-feed graph. (Constants: CEA 90\({}^{\circ}\), diameter 14.75 mm, depth of cut 0.5 mm. Variables: n1: 480 rpm, n2: 630 rpm, n3: 1250 rpm). In Figure 9, the sample was machined on a lathe with a feed of 0.028 mm per revolution and a fixed depth of cut of 0.5 mm. This study explored the impact of varying the cutting-edge angle on surface roughness. The results from rigorous research revealed that the lowest average surface roughness recorded was 1.228 um. This was achieved at a cutting-edge angle of 90\({}^{\circ}\) and a spindle speed of 480 rpm. In contrast, the highest average surface roughness measured was 2.711 um, which occurred at a cutting-edge angle of 70\({}^{\circ}\) and a spindle speed of 1250 rpm. These findings significantly advance our understanding of machining parameters and their effects on surface roughness. In Figure 9, average surface roughness measurements are labeled as Ra1 for the spindle speed n1, while Ra2 and Ra3 correspond to measurements for the other spindle speeds. It was noted that the value obtained at n1 is more suitable for practical applications than those at n2 and n3. For a feed of 0.028 mm/rev and a fixed pass depth of 0.5 mm, the optimal operating parameters to achieve the best average surface roughness are a spindle speed of 480 rpm and a cutting-edge angle of 90\({}^{\circ}\). Under these conditions, the achieved Ra value was 1.228 um. The graph indicates a general trend of decreasing average surface roughness as the cutting-edge angle increases, reinforcing the practicality of this research and its implications for the industry by providing a clear roadmap to achieve optimal surface roughness. Figure 10 shows the change in surface roughness depending on the change in spindle speed. This study has some constants: the cutting-edge angle is 70\({}^{\circ}\), the workpiece diameter is 14.75 mm, and the cutting depth is 0.5 mm. For different spindle speeds, one of the three feed values corresponds to a certain one (f1: 0.028 mm/rev, f2: 0.088 mm/rev, and f3: 0.155 mm/rev). Figure 10 shows that the surface roughness value increases with the  
Figure 8: Surface roughness-cutting-edge angle graph. (Constants; feed 0.088 mm/rev, depth of cut 0.5 mm, diameter 14.75 mm. Variables: n1: 480 rpm, n2: 630 rpm, n3: 1250 rpm).