3.3.2. T2—Produced Surface Roughness

Regarding the Ra values obtained for the tests conducted using T2 tools, these can be observed in Table 9.



As seen from Table 9, the Ra values measured in the tangential and radial directions were very similar, meaning that there were no excessive vibrations produced during the machining tests. From the surface roughness values analysis, it was observed that, as seen from the results of the tests using T1, the surface roughness was lower for lower feed values. Furthermore, the cutting length also had a clear influence in the machined material's surface quality, registering a clear increase in surface roughness for the tests conducted ata4m cutting length. Once again, the highest surface roughness value was obtained under the condition of a 4-m cutting length and higher feed rate value (125%). It is also worth noting that the increase in surface roughness value from a 75% to 100% feed rate was less accentuated than the increase registered from a 100% to 125% feed rate. This was a similar behavior to that observed in the tests conducted with T1.

### 3.3.3. T3—Produced Surface Roughness

In Table 10, the average calculated values of Ra from the surface roughness measurements conducted on the machined material (using T3 tools) can be observed.

**Table 10.** Average surface roughness values, measured in the radial and tangential directions for the tests conducted with T3.


Comparing the values shown in Table 10 to those obtained from the tests conducted with the previous tools (T1 and T2), it was observed that the Ra values were quite lower for the tests performed with the T3 tools. Analyzing the variation of Ra values with the different test conditions, similarly to the previously presented results, showed that the surface roughness values tended to increase for higher cutting lengths. However, there was a different trend noticed with the feed variation. Unlike what was observed for the other test conditions, a significant decrease in surface roughness values were registered for higher feed rate test conditions (125%), with these producing, by far, the best surface quality registered to this point. In this case, the worst surface quality was obtained under the test condition of 4 m of cutting length while using the original feed rate (T3L4F100). The lowest value of Ra was obtained under the condition of a 2-m cutting length, using 125% of the original feed rate (T3L2F125).

### 3.3.4. T4—Produced Surface Roughness

In this subsection, the surface roughness results for the machining tests conducted with T4 tools are presented. The average values of the measured Ra (in both radial and tangential directions) parameter can be observed in Table 11. As seen in the previous subsections regarding the surface roughness results obtained using the different tools, surface roughness varies with the cutting length and feed rate values.


**Table 11.** Average surface roughness values, measured in the radial and tangential directions for the tests conducted with T4.

From the analysis of Table 11, it was concluded that the process was stable, as the values for Ra measured in the tangential and radial directions did not deviate significantly from each other. The variation in Ra values for different parameters was like the variation observed in the tests conducted with T1 and T2 tools. Once again, the 2-m cutting length test condition produced the best surface roughness quality, with this deteriorating with the increase in this parameter, as observed in all the analyzed tools. Regarding the variation of Ra with the feed rate, as previously mentioned, it was observed that the lowest Ra value was obtained by using lower feed rate values, with the surface quality quickly deteriorating with the increase in feed rate.

## *3.4. Flank Wear Measurements*

The wear measured in the tools' flanks for each test condition is presented in this section in numerical form, presenting the average values of flank wear, as well as in graphical form, enabling for a clear perception on how this wear varies with the machining parameters. These values were measured on the clearance faces of all the tested tools, following the standard ISO 8688-2:1989 [52], as mentioned in Section 2. As in the previous Section 3.3., these values are in different subsections, one for each of the analyzed tools, with an extra section dedicated to the comparison of the flank wear values obtained.
