## 3 Results  
The response of the AE signal (envelope) to the MDF milling process under each cutting condition is shown in Figure 6.  
Figure 5: Analyzed areas of the milled plate in detail. Figure 6: Comparison of the response of the AE signal to the MDF milling process under each cutting condition (rotation speed/feed rate): (**A**) 10,000 rpm/6 m.min\({}^{-1}\), (**B**) 10,000 rpm/12 m.min\({}^{-1}\), (**C**) 20,000 rpm/6 m.min\({}^{-1}\), (**D**) 20,000 rpm/12 m.min\({}^{-1}\). As shown in Figure 7, at the maximum speed (20,000 RPM) and maximum feed rate (12 m.min\({}^{-1}\)), there was only one significant increase in the signal (package). Reducing the feed rate by half had no substantial effect on the character of the signal. For better orientation, markers were placed on the logs to indicate the significant influence of the cutting edge on the machining process (red circle) and weak or negligible influence (red cross). However, when the speed was halved to 10,000 RPM, and regardless of whether the feed remained the same or was reduced to 6 m.min\({}^{-1}\), the cutter clearly engaged all the cutting edges with a single dominant package--see Figure 8.  
The statistical analysis aimed to evaluate whether the experimental cutting conditions labeled A, B, C, and D in Table 4 significantly influenced the measured AE signals during the CNC milling process. Each cutting condition was repeated six times, providing a sufficient sample size for a robust statistical evaluation. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Labeling**} & **Tool Revolution** & **Feed Speed** & **Number of Revolutions** & **Number of Data** \\  & **(rev.min\({}^{-1}\))** & **(m.min\({}^{-1}\))** & **per One Cut** & **Number of Data** \\ \hline A & 10,000 & 6 & 833 & \(n=61,324\) \\ B & 10,000 & 12 & 417 & \(n=31,132\) \\ C & 20,000 & 6 & 1667 & \(n=61,326\) \\ D & 20,000 & 12 & 833 & \(n=31,156\) \\ \hline \end{tabular}
\end{table} 
Table 4: Labeling of cutting conditions and corresponding number of measurements for statistical analysis. Figure 7: Records of individual milling stages (I-II-III)—detailed view for following cutting conditions (rotation speed/feed rate): (**1**) 20,000 rpm/12 m.min\({}^{-1}\), (**2**) 20,000 rpm/6 m.min\({}^{-1}\). Table 4 shows that the individual experimental cutting conditions were conducted at different CNC tool speeds. Consequently, the AE signal data were normalized and referenced to a standard of one revolution per cut. Table 5 presents a comparison of the selected descriptive statistical parameters of the AE signal values, both for the original measurements and for the normalized values. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Cutting** \\ **Conditions** \\ \end{tabular} } & \multirow{2}{*}{**Measurement**} & \multicolumn{3}{c}{**AE Signal**} & \multicolumn{3}{c}{**AE Signal**} \\ \cline{3-8}  & & **Avrage** & **Sum** & **SD** & **Average** & **Sum** & **SD** \\ \hline \multirow{8}{*}{A} & 1 & 67.041 & 684,220.034 & 4.978 & 0.079 & 804.977 & 0.006 \\  & 2 & 65.116 & 666,785.827 & 5.663 & 0.077 & 784.445 & 0.007 \\  & 3 & 65.225 & 666,469.970 & 5.429 & 0.077 & 784.030 & 0.006 \\  & 4 & 65.391 & 668,553.260 & 5.424 & 0.077 & 786.524 & 0.006 \\  & 5 & 65.314 & 667,901.824 & 5.602 & 0.077 & 785.744 & 0.007 \\  & 6 & 65.407 & 667,805.955 & 5.375 & 0.077 & 785.668 & 0.006 \\ \hline \multirow{8}{*}{B} & 1 & 69.621 & 361,330.751 & 4.606 & 0.080 & 416.771 & 0.005 \\  & 2 & 67.891 & 351,810.091 & 4.630 & 0.078 & 405.792 & 0.005 \\ \cline{1-1}  & 3 & 67.836 & 351,119.527 & 4.717 & 0.078 & 404.976 & 0.005 \\ \cline{1-1}  & 4 & 69.549 & 361,097.696 & 4.727 & 0.080 & 416.511 & 0.005 \\ \cline{1-1}  & 5 & 67.967 & 352,477.798 & 4.981 & 0.078 & 406.565 & 0.006 \\ \cline{1-1}  & 6 & 67.965 & 353,824.205 & 4.933 & 0.078 & 408.081 & 0.006 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of descriptive statistical parameters of AE signal values before and after normalization.