## 3 Results
### Quality Evaluation of the CNC Milled Surfaces
#### 3.2.4 Influence of Wood Anatomy on Surface Roughness  
When comparing the two species, the Ra values seemed consistently higher for oak than for maple across all machining conditions. However, Ra proved insufficient for fully describing the surface quality, as it is highly sensitive to the presence of large vessels. The Abbott-Firestone parameters provide instead a deeper insight into the stratified structure of processed wood surfaces. Although both wood species were machined using identical parameters, their surface responses differed notably due to their anatomical characteristics. Maple, a diffuse-porous species with fine and uniformly distributed vessels, generally produced smoother surfaces, particularly when milled with the straight-edged tool (T2). Its consistent texture contributed to lower Rk and Rpk values (Table 3) and resulted in a more predictable response to variations in the processing conditions.  
In contrast, oak, a ring-porous species with large earlywood vessels and prominent rays, showed greater surface deterioration, especially when processed with the helical tool (T1). This was attributed to the uneven cutting resistance within its growth rings, caused by abrupt transitions between earlywood and latewood, which led to a fluctuating tool engagement and local fiber tearing. Although oak has a higher overall density than maple, a characteristic that would typically improve machinability, the disruptive effect of its anatomical heterogeneity proved dominant. As a result, the oak surfaces exhibited more pronounced roughness and morphological defects, despite the greater density of the material. Across most parameter combinations, oak exhibited higher Rk, Rpk, and Rpkvalues (Table 5), and the microscopic analysis revealed more frequent fiber disruption and visible tool marks.  
Although machining could not fully replicate the anatomical clarity of super surfacing, the tool T2 consistently demonstrated superior performance compared to T1 in minimizing the core roughness and preserving the surface morphology during maple and oak CNC milling. These findings are consistent with the results reported by [38], who also found that straight-end mills produced smoother surfaces than spiral tools across various wood species, including beech and pine. The authors explained that the geometry of the straight edge, which cuts in a more planar and uniform manner, allows for better surface preservation by minimizing lateral fiber disruption. Although no study was found in the literature about an identical tool-wood material parameter setup, the minimum Ra values obtained in this research for maple and oak for the optimal combination (T1 tool, minimum stepover and depth of cut) were similar to the Ra values in other studies, which achieved optimal surface quality using end-mill or planing tools (Sections 3.2.2 and 3.2.3).  
Future research will give particular attention to the face milling of radial surfaces in order to observe the influence of grain orientation (radial-tangential) on surface quality after processing in identical conditions. Since both end tools are designed not only for face milling but also for edge/side milling, another research target will be to compare the tools' performance in relation to the surface quality of processed edges and understand the influence of grain orientation and of the tool active part during CNC milling. The clear differentiation between tangential and radial surface responses is essential to define machining strategies that are anatomically tailored.  
In addition, the experimental scope will be extended to include representative species from other hardwood categories, such as diffuse-porous, semi-ring-porous, and ring-porous groups, in order to capture the variability in surface formation mechanisms during face and edge milling. This comparative approach will help clarify whether the tool-material interactions observed for oak and maple are consistent across broader anatomical typologies or whether species-specific adjustments are required for optimal surface outcomes.