*3.3. Surface Roughness Analysis*

In this section, the surface roughness analysis results are presented, showing the average Ra values for the tangential and radial measurement directions, as any deviation between these values of roughness indicates instability during machining, usually presenting as a higher level of vibration during the cutting operation. These results are divided into subsections, one for each of the tested tools, with an extra subsection where the comparison between the tools, regarding the roughness values, is presented. The adopted procedure is described in detail in Section 2.

### 3.3.1. T1—Produced Surface Roughness

The average surface roughness values that were measured in the material machined with the T1 tools are presented in Table 8. These were used to create surface graphs to depict the surface roughness variation for all the tested conditions. Table 8 adopted the tool reference described in Section 2.

**Table 8.** Average surface roughness values, measured in the radial and tangential directions for the tests conducted with T1.


From the values presented in Table 8, it was observed that the values measured in the tangential and radial directions are very similar. However, this deviation was not significant. Thus, it can be concluded that in this case, the machining process itself was stable.

By analyzing the surface roughness values measured for both directions, it was observed that they follow a similar trend of rising with the cutting length; i.e., tests conducted with the tool with the 2-m cutting length produced the best results in terms of surface roughness. This was due to the tool's wear, which was aggravated for higher cutting lengths. Another parameter that seemed to influence the surface roughness of the material was the feed rate, as it was observed for lower feed rates that the tools produce a better surface quality. From the lowest feed rate value to the original, a slight increase in surface roughness was registered; however, for feed rates of 125%, the surface roughness that was produced was the highest registered, with the maximum produced under the condition of 4 m of cutting length while using 125% of the original feed rate (T1L4F125).
