## 3 Results and Discussion
Figure 7: Surface roughness-cutting-edge angle graph. (Constants; feed 0.155 mm/rev, depth of cut 0.5 mm, diameter 14.75 mm. Variables: n1: 480 rpm, n2: 630 rpm, n3: 1250 rpm). increase in feed value. This change is consistent with the literature. Figure 10 measured the largest surface roughness (1250 rpm\(-\)0.155 mm/rev) as 4.745 \(\upmu\)m. Figure 10 measured the most minor surface roughness (630 rpm\(-\)0.028 mm/rev) as 2.282 \(\upmu\)m. The selected operating parameters here show that the machine operating parameters that can cause the lowest surface roughness are 630 rpm and 0.028 mm/rev. The increment between the first two revolutions is low, while the increment between the second and third revolutions is more than four times the first increment. In this case, in the experimental design, it is seen that the roughness value increases even more with growing high revolutions, especially if large feeds are preferred. Of course, tool-part materials are essential when determining the material removal parameters. However, together with the machining methods that give movement to the tool and the part and are formed according to these movements, it is also essential to know the machine's usable revolutions and feed values. In addition, the rigidity of the machine is also significant for obtaining good surface quality. Figure 11 shows the spindle speed-surface roughness change. The fixed parameters used in the experiments are a cutting-edge angle of 80\({}^{\circ}\), a diameter of 14.75 mm, and a cutting depth of 0.5 mm. In these experiments, for each spindle speed, three different feed values (f1: 0.028 mm/rev, f2: 0.088 mm/rev, and f3: 0.155 mm/rev) correspond. In other words, for each feed, experiments were carried out with three-spindle speed changes (n1: 480 rpm, n2: 630 rpm, and n3: 1250 rpm), and graphs were drawn. In Figure 11, the surface roughness also increased when the spindle speed increased at the feed value of 0.155 mm/rev. This situation confirms the literature that when the feed value remains constant, the spindle speed increase positively affects surface roughness. This experimental  
Figure 10: Surface roughness-rpm graph. (Constants; CEA 70\({}^{\circ}\), depth of cut 0.5 mm, diameter 14.75 mm. Variables: f1: 0.028 mm/rev, f2: 0.088 mm/rev, f3: 0.155 mm/rev). Figure 9: Surface roughness-cutting-edge angle graph. (Constants; feed 0.028 mm/rev, depth of cut 0.5 mm, diameter 14.75 mm. Variables: n1: 480 rpm, n2: 630 rpm, n3: 1250 rpm). study also observed that the surface roughness decreases with the increase in spindle speed obtained for the other two feed values. With the experimental study parameters, the largest surface roughness (480 rpm, 0.155 mm/rev) was obtained as 2.956 \(\upmu\)m, and the smallest surface roughness (1250 rpm, 0.028 mm/rev) was obtained as 1.181 \(\upmu\)m.  
Figure 12 shows the variation in surface roughness with spindle speed when the cutting-edge angle is 90\({}^{\circ}\). Figure 12 shows the measured surface roughness for each spindle speed parameter, corresponding to three feeds (f1: 0.028 mm/rev, f2: 0.088 mm/rev, and f3: 0.155 mm/rev). Figure 12 shows that the largest surface roughness (480 rpm, 0.155 mm/rev) is 2.457 \(\upmu\)m, and the minor surface roughness (480 rpm, 0.028 fee/rev) is 1.228 \(\upmu\)m. The surface roughness decreased with the increasing spindle speed value (in the machining with the 0.155 mm/rev parameter). The curve given by the values measured in the machining performed with feed f1: 0.028 mm/rev showed the opposite of the previous situation. In this case, the increasing spindle speed increased the surface roughness. In the machining performed with feed f2: 0.088 mm/rev, the growing spindle speed (from 480 rpm to 630 rpm) primarily caused a decrease in the surface roughness. When the spindle speed increased from 630 rpm to 1250 rpm, the surface roughness increased.