## 3 Results and Discussion
In Figure 5, the sample was machined on a lathe with the tool's cutting-edge angle set at 80\({}^{\circ}\) and a depth of cut of 0.5 mm. We specifically investigated how variations in feeds, a key machining parameter, affected surface roughness. The graph shows that the lowest average surface roughness value recorded was 1.769 \(\upmu\)m, achieved at a feed of 0.028 mm/rev and a spindle speed of 1250 rpm. In contrast, the highest average surface roughness value was 2.956 \(\upmu\)m, occurring at a feed of 0.155 mm/rev and a spindle speed of 480 rpm. In the figure, Ra1 represents the average surface roughness measurement obtained at spindle speed n1, while Ra2 and Ra3 correspond to similar measurements. The results indicate that the value associated with spindle speed n3 is more favorable for practical applications than n1 and n2, aligning with findings in the existing literature. This suggests that for a cutting-edge angle of 80\({}^{\circ}\), the optimal working parameters were determined to be a spindle speed of 1250 rpm with a feed of 0.028 mm/rev, resulting in an average Ra value of 1.769 \(\upmu\)m, which can be applied in real-world manufacturing scenarios. In Figure 5, while the increment between the feed values is equal, the increment between the spindle speed numbers increases from small to large, respectively. The increment amounts between the variable spindle speed numbers are variable. When the surface roughness curves obtained from the experiments carried out, in this case, are examined, the effect of the decreasing feed value and increasing spindle speed number on the surface roughness is positive. In Figure 6, the sample was machined on a lathe with the tool's cutting-edge angle set at 90\({}^{\circ}\) and a depth of cut of 0.5 mm. The investigation focused on how varying feeds affected surface roughness. The analysis revealed that the minor average surface roughness, measured at 1.228 \(\upmu\)m, occurred at a feed of 0.028 mm/rev and a spindle speed of 480 rpm. Figure 4: Surface roughness-feed graph. (Constants: CEA 70\({}^{\circ}\), diameter 14.75 mm, depth of cut 0.5 mm. Variables: n1: 480 rpm, n2: 630 rpm, n3: 1250 rpm). Figure 5: Surface roughness-feed graph. (Constants: CEA 80\({}^{\circ}\), diameter 14.75 mm, depth of cut 0.5 mm. Variables: n1: 480 rpm, n2: 630 rpm, n3: 1250 rpm). Conversely, the largest average surface roughness measured was 2.456 \(\upmu\)m at a feed of 0.155 mm/rev while maintaining the same spindle speed of 480 rpm. In Figure 6, the average surface roughness values Ra1, Ra2, and Ra3 correspond to measurements taken at different operating spindle speeds, with Ra1 at n1 spindle speed being more suitable for practical applications than the others. For a cutting-edge angle of 90\({}^{\circ}\), the optimal average surface roughness was observed at a spindle speed of 480 rpm and a feed of 0.028 mm/rev, resulting in a Ra value of 1.228 \(\upmu\)m. Additionally, the graph indicates that at a feed of 0.155 mm/rev, surface roughness decreased as the spindle speed increased. However, this combination did not yield the lowest surface roughness value compared to the feed of 0.028 mm/rev, which is particularly noteworthy. In Figure 7, the sample was machined on a lathe with a feed of 0.155 mm and a fixed depth of cut of 0.5 mm. This study focused on how cutting-edge angle variations affected surface roughness. The smallest recorded average surface roughness value was 2.056 \(\upmu\)m, which occurred at a tool cutting-edge angle of 90\({}^{\circ}\) and a spindle speed of 1250 rpm. In contrast, the largest average surface roughness value was 4.745 \(\upmu\)m, observed at a cutting-edge angle of 70\({}^{\circ}\) while maintaining the same spindle speed of 1250 rpm. In Figure 7, the average surface roughness measurements--Ra1, Ra2, and Ra3--correspond to the values obtained at spindle speeds n1, n2, and n3, respectively. It was noted that the value obtained at n3 is more suitable for practical applications than n2 and n1.