## 4 Conclusions  
This study has shown that the surface quality should be analyzed on stratified levels of irregularities differentiating between, waviness, tool marks, fuzzy grain, and accidental surface gaps overlapped onto the deep anatomical cavities of the wood, such as pores from earlywood. This is because the milling quality will be dependent not only on the processing parameters and tool characteristics, but also on the wood species and its anatomical structure. The interpretation of the results was focused on variations in \(\
u_{\mathrm{f}}\), respectively n, since f\({}_{\mathrm{z}}\) is directly influenced by the feed speed v\({}_{\mathrm{f}}\) for a constant n and for the same number of cutters (a single type of tool was used in this research), while the cutting speed, v\({}_{\mathrm{c}}\), differs very slightly with the local tool diameter (depth of cut, respectively), for a given rotation speed, n.  
An increase in the feed speed, v\({}_{\mathrm{f}}\), increases tool vibration, which leaves deeper waves in the surface. The surface waviness measured by Wa increased more than double when the feed speed increased approximately 3.6 times, from v\({}_{\mathrm{f}1}\) = 6.53 m/min, to v\({}_{\mathrm{f}2}\) = 23.74 m/min. Increasing the rotation speed from n\({}_{1}\) to n\({}_{2}\) (double) has decreased Wa with 20%, but without statistical support. An increase in the feed speed increases the toolmarks approximated by Rk which are more pronounced as the rotation speed becomes higher. Rk increased with the feed speed (respectively, f\({}_{\mathrm{z}}\) for a constant n and number of cutters) for n\({}_{2}\) = 6594 rot/min by a significant 57%. An increase in the rotation speed from n\({}_{1}\) to n\({}_{2}\) has reduced Rk, but the effect was not significant. For example, an increase in the rotation speed from n\({}_{1}\) to n\({}_{2}\) decreased Rk by approximately 16% for the v\({}_{\mathrm{f}1}\) feed speed. Similar behavior was noticed for the Ra parameter. The processing quality (Rk) measured at different depths did not differ statistically, in spite of the local differences in the cutting speed. An increase in the feed speed raises the wood fiber. Therefore, the Rpk parameter increased 2.4 times when the feed speed increased 3.6 times. The increase in the rotation speed does not produce any significant effect regarding fuzziness or raised fiber. Wood pores were deeper than the marks left by the tool on the wood and their effect on surface quality was disregarded in the above conclusions. However, some gaps deeper than the core roughness and caused by material detachment were noticed when the milling encountered radial surfaces, thus affecting the ray tissues. This did not change the conclusion that the smoothest beech surface is obtained when the smallest feed speed (6.53 m/min) is used. However, by including the surface gaps in the analysis by referring to the parameter Rk+Rpk+Rvk, it attributed a significance to the rotation speed as well, such as the higher rotation speed (6594 rot/min) also contributing to the surface quality improvement. The processing quality measured at different depths does not differ statistically, in spite of the local differences in the cutting speed. The statistical analysis helped us to understand the hierarchy of influence factors and their significance. In this respect, the most important factor affecting the surface quality was the feed speed. The moment of measuring the surface roughness, such as immediately after sharpening or after a working period, influences the result of the surface quality. Measurementsof surface quality after the tool processed 600 m of beech material improved the surface quality by 30%. In further work, such stratified analysis will provide a more in-depth understanding and quantification of the tool interaction with the wood material and will help the selection of the most appropriate processing parameters as a function of the tool and species variables. Conceptualization, L.-M.B. and L.G. ; data curation, L.-M.B. and L.G.