## 1 Introduction
[5] showed that machining method and fiber orientation significantly influence surface roughness in beech and aspen, while [6] reported that feed rate and cutting angle affect the surface quality of sessile oak, emphasizing species-specific sensitivity to tool geometry. Additionally, [PERSON]. [7] noted that anatomical traits such as vessel diameter and fiber interlocking can outweigh bulk density in determining surface roughness, especially in tropical species. Furthermore, [PERSON]. [8] identified feed rate and spindle speed as key factors in reducing roughness when CNC face milling palm wood, reinforcing the importance of process control. To this body of evidence, [PERSON]. [9] added information by demonstrating that lower feed speeds (10 m/min compared to 30 m/min), using a Weinig Unimat 500 planer (Tamex, Sarajevo, Bosnia and Herzegovina), significantly decreased surface roughness in oak, yielding results comparable to those achieved by combined planing and sanding using a Viet Opera V machine. Most recently, [PERSON]. [3] explored the CNC face milling of Anatolian chestnut using high-speed steel straight-end mills (\(\phi\) = 8 mm, 3 flutes) and found that the lowest Rz values were achieved at the spindle speed of 16,000 rpm and with the depth of 10 mm, confirming the importance of tool configuration and cutting strategy in optimizing surface quality. Ring-porous species like oak exhibit pronounced variation in the cutting resistance between earlywood and latewood, even under identical machining settings. It was observed [7] that radial sections generally show higher roughness than tangential ones due to fiber interlock and vessel arrangement, especially when measured perpendicular to the grain. In a broader comparative study involving tropical hardwoods such as Garapa, Tatajuba, Wenge, and Merbau, the above author further found that the surface roughness values for measurements perpendicular to the grain were nearly double those measured along the grain, underlining the critical role of the anatomical structure (cell cavities) in shaping the surface texture. While investigating several machining approaches, including face milling and super surfacing (shaving), [PERSON]. [10] found that microstructural integrity played a crucial role in determining the tensile shear strength of glued joints. They observed that super surfacing, when using sharp, rounded tools, preserved subsurface quality and improved the bonding behavior--findings that directly support the use of super surfacing as a benchmark in our studies. Similarly, [PERSON]. [11] reported superior bonding on face-milled beech surfaces compared to conventionally planed ones, provided that the milling process was optimized to avoid excessive fiber damage. These observations highlight that achieving a smooth surface is not sufficient on its own; the underlying structure must also remain intact to ensure functional performance. From a process control perspective, surface quality in face milling is influenced by factors such as tool entry direction, with climb milling generally resulting in less cell compression and more uniform textures [10]. Feed rate and tool sharpness also play a key role in minimizing subsurface damage, even when surface roughness appears acceptable [12]. Moreover, due to the inherent heterogeneity of wood, including variations in fiber orientation and vessel structure, machining strategies must often be tailored to each species. As [6] observed, parameters effective for one anatomical configuration may not be directly transferable to another without careful adjustment. In summary, surface quality in hardwood machining results from a complex interaction between process parameters, tool design, and wood anatomy. While conventional cutter blocks are suitable for flat surfaces, they lack the precision and adaptability needed for intricate components. CNC-based fronto-lateral end mills offer greater flexibility and accuracy, yet studies on their performance in the face milling of wood remain limited.