## 3 Results
### Quality Evaluation of the CNC Milled Surfaces
#### 3.2.3 Surface Roughness and Stereomicroscopy Analysis for CNC-Processed Oak
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**ANOVA** & & & & & & \\
**Source of Variation** & **SS** & **df** & **MS** & **F** & **\(p\)-Value** & **F crit** \\ \hline Rows & 4.826416 & 3 & 1.608805 & 0.70846801 & 0.5708396 & 3.862548 \\ Columns & 81.74111 & 3 & 27.24704 & 11.99875198 & 0.0016932 & 3.862548 \\ Error & 20.4374 & 9 & 2.270823 & & & \\ Total & 107.0049 & 15 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Two-way ANOVA without replication for oak, with a stepover of 5 mm. Figure 13: Comparative microscopic images of oak processed by T1 and T2 at the cutting depth of 1 mm and of the reference surface. In general, the increase in stepover produced more fuzzy grain, which is seen in the Rpk values in Table 5 for a depth of cut of 1 mm and in the micrographs of Figure 13.  
The Rvk and Rv values offer further insight into the depth of the surface valleys formed during machining. For oak, the Rv values reached up to 264.37 \(\upmu\)m (T2 at 9 mm), which aligns with the anatomical data reported in the literature, according to which oak vessel diameters range from 350 to 500 \(\upmu\)m [33]. The shaved reference surface showed a mean Rv of 165.04 \(\upmu\)m, indicating that the deepest valleys observed in the CNC-processed surface were primarily related to the exposure of earlywood vessels cavities rather than to excessive tool penetration or machining defects. Figure 14: Comparative micrographs of oak processed by T2, for 2 cutting depths and 3 stepover values. Magnification \(120\times\); h represents cutting depth. Figure 15: Comparative micrographs of oak processed by T1, for 2 cutting depths and 3 stepover values. Magnification \(120\times\); h represents cutting depth. Figure 13 illustrates microscopic images of oak surfaces machined with T1 and T2, for three values of stepover at a cutting depth of 1 mm, compared with the reference shaved surfaces, while Figures 14 and 15 show a comparison of the effect of the cutting depth for each tool type. The super surfaced reference images revealed a clean-cut anatomical structure, with distinctive types of cells with their corresponding open lumens and with negligible surface damage, almost like that of a microtomed surface. As in the case of map, the surface processed with T2 at a stepover of 5 mm resembled the reference surface best, and this is also visible in the roughness profiles in Figure 12. For both tools, an increase in the stepover value worsened the surface quality (Figure 13). This was noticed for T1, as shown by the prominent tool marks appearing as regular ridges across the grain, in addition to material detachment and fuzziness, indicating a more aggressive cutting action that disturbed the anatomical integrity of the surface. The helical geometry of T1, while typically advantageous for chip evacuation, generates angled shear forces that may tear across earlywood vessels and ray tissue. This effect is particularly evident in ring-porous species like oak, where large earlywood pores and broad multiseriate rays lead to a non-uniform cutting resistance across the surface. On the other hand, the tool T2, with its straight cutting edges, resulted in a cleaner cut, preserving more successfully the integrity of anatomical features such as vessel boundaries and ray patterns. Although the ANOVA test indicated a significant increase in the core roughness for a cutting depth of 3 mm, it was more difficult to discern any difference in quality caused by the two depths of cut in the case of the T2 tool, as shown in Figure 14; the amount of damage looked similar, while the best surface quality was clearly obtained for a stepover value of 5 mm. A visual examination of the microscopic images in Figure 15 indicated that for oak processed by the T1 tool, the surface quality decreased with an increase in the stepover and depth of cut. Apart from the pull-out material, the quality was affected by the pronounced ridges imprinted by the T1 tool across the grain.