## 3 Results
### Quality Evaluation of the CNC Milled Surfaces
#### 3.2.2 Surface Roughness and Stereomicroscopy Analysis of CNC-Processed Maple
The values in brackets represent the cutting depth. Concerning the stepover influence over the Rk parameter, a significant increase in Rk with the stepover value was found for T1 at the 1 mm depth of cut and for T2 at the 3 mm depth of cut, as tested by ANOVA without replication. Although the values of Rk for T2 and 1 mm depth of cut were similar (Table 3), the overall quality worsened with the increase in the stepover due to an increase in fuzziness and fiber detachment, which can be seen from the increase in the Rpk values in Table 3, as well as from the protuberances in the roughness profiles in Figure 7 or in the aspect of the micrographs in Figure 8. Increasing the depth of cut to 3 mm increased the core surface roughness Rk as well as the fuzziness (Rpk) in comparison with the values at 1 mm depth, and this trend increased as the value of the stepover increased (Figure 9). This showed that an increase in the depth of cut combined with an increasing stepover led to a significant deterioration in surface quality, the T2 cutter becoming more sensitive to the operating parameters under conditions of increased effort. Overall, T2 showed a clearer quality trend with changes in the cutting depth and stepover than T1, for which the quality variation was rather unpredictable. \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 & 0.062338 & 3 & 0.020779 & 0.055278 & 0.981819336 & 3.8625484 \\ Columns & 32.53002 & 3 & 10.84334 & 28.84625 & 6.00666 \(\times\) 10\({}^{-5}\) & 3.8625484 \\ Error & 3.383111 & 9 & 0.375901 & & & \\ Total & 35.97547 & 15 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Two-way ANOVA without replication for maple, at a stepover of 5 mm. Figure 7: Comparative roughness profiles for maple processed by the tools T1 and T2 at the cutting depth of 1 mm and reference profile: red—shared surface, navy blue—stepover 5 mm, magenta—stepover 7 mm, and light blue—stepover 9 mm. For visualization clarity, each roughness profile is vertically offset relative to its own baseline; the vertical positioning does not reflect the absolute height differences between conditions. Figure 8: Comparative microscopic images of maple processed by T1 and T2 at the cutting depth of 1 mm and of the reference surface. Magnification 120\(\times\). Figure 9: Comparative micrographs of maple processed by T2 for 2 cutting depths and 3 stepover values. Magnification 120\(\times\); h represents cutting depth. For maple, Rv ranged from 59.52 \(\upmu\)m to 74.27 \(\upmu\)m for the 1 mm cutting depth and from 43.71 \(\upmu\)m to 76.74 \(\upmu\)m for the 3 mm cutting depth. The reference surface obtained by shaving exhibited Rv effective values from 42 to 49 \(\upmu\)m, indicating that a substantial portion of the surface valleys were due to the natural anatomical structure of the wood. According to [33], the vessel diameters in maple typically range from 30 to 70 \(\upmu\)m but can occasionally reach 110 \(\upmu\)m, which corresponds well with the Rv values observed. This means that the deepest valleys measured by Rv and seen also in the roughness profiles of Figure 7 belonged to the vessel cavities opened during the cutting process. To gain deeper insights, comparative roughness profiles and corresponding microscopic images were examined. The roughness profiles selected were for both tool types (T1 and T2) at the 1 mm cutting depth and for all three stepover values, as presented in Figure 7. The roughness profiles in Figure 7 are color-coded: red represents the shaved surface, navy blue corresponds to milling with a 5 mm stepover, magenta to milling with a 7 mm stepover, and light blue to milling with a 9 mm stepover. At a cutting depth of 1 mm, the roughness profiles in Figure 7 revealed that the tool T2 (with straight blades) produced a cleaner surface finish compared to T1 (with helical blades).