## 2 Materials and Methods
Dominant frequencies were summarized. In most cases, when no parameters changed, they remained similar. A summary of their averages is shown in Figure 8.  
Next, to determine if vibrations on the gripper could be used as a signal for adaptive control, the dependency between cutting parameters and single-sided amplitude spectrum amplitudes were assessed by analysis of variance (ANOVA). This analysis was conducted for significance level p = 5%. Figure 9 shows the dependency of amplitudes when changing spindle rotation from 10,000 to 20,000 min\({}^{-1}\). As the revolutions increased, the vibration amplitudes also increased. Figure 7: Scheme of experiment procedure. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{2}{c}{**G3 X**} & \multicolumn{3}{c}{**G3 Z**} & \multicolumn{3}{c}{**G4 X**} & \multicolumn{3}{c}{**G4 Z**} \\ \(f\) **(Hz)** & **Maxima** & \(f\) **(Hz)** & **Maxima** & \(f\) **(Hz)** & **Maxima** & \(f\) **(Hz)** & **Maxima** \\ \hline
165.93 & 0.93 & 166.13 & 0.80 & **165.93** & **1.92** & 166.13 & 3.26 \\
**498.20** & **1.56** & 332.26 & 0.85 & 498.39 & 1.86 & 332.06 & 0.96 \\
1328.06 & 0.84 & **498.20** & **5.15** & 829.67 & 0.57 & **498.20** & **9.72** \\
1494.19 & 0.58 & 664.33 & 1.10 & 996.19 & 0.94 & 664.33 & 1.30 \\  & & 830.26 & 1.22 & & & 830.26 & 1.38 \\  & & 996.39 & 2.12 & & & 996.19 & 0.76 \\  & & 1162.52 & 0.69 & & & & \\  & & 1328.65 & 0.51 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Example of filtered output from fast Fourier transform. Figure 10 shows the dependency of amplitudes when changing the spindle rotations for different materials. When milling particleboard, amplitudes were lower than in milling MDF board. Figure 8: Summary of dominant frequency maxima though range of parameters. Figure 9: Box plot of 95% confidence interval of amplitude dependency on spindle rotation. Figure 11 shows the dependency of amplitudes when changing feed rate for different experimental materials. As the feed rate increased, amplitudes increased at milling MDF boards bud decreased at milling particleboards. Figure 12 shows the dependency of amplitudes for different tools and experimental materials. The razor mill produced higher amplitudes of vibrations than the spiral mill at both experimental materials. Figure 11: Box plot of 95% confidence interval of amplitude dependency on material and feed rate. Figure 10: Box plot of 95% confidence interval of amplitude dependency on material and spindle rotation. were observed at 332.26 Hz and 498.2 Hz. These, with rest of peaks, presented multiples of the first value. In some cases, multiples are not seen in Table 5. However, these were still present, but with maxima smaller than 0.5;0 they were filtered out. Similar results were observed through use of all parameters. Therefore, it seems the main vibrations were caused by the rotating tool. This theorem would be supported by the maxima summary shown in Figure 8. When maxima from spindle rotation \(n\) = 10,000 min\({}^{-1}\) are compared, the vibrations in \(x\) axis seem smaller or equal to axis \(z\). As expected, the spiral mill produced higher results mainly in the \(z\) axis. With higher cutting speed \(n\) = 20,000 min\({}^{-1}\), the use of spiral mill produced larger maxima, which mostly seemed equally high in both \(x\) and \(z\) axis. When comparing results from variance analysis, almost all parameter changes significantly affected the results. In Figure 9, the results show that the spindle speed had an effect on amplitude overall, with values in range (2.28-2.85) for \(n\) = 10,000 min\({}^{-1}\) and (2.95-3.7) for \(n\) = 20,000 min\({}^{-1}\). The significance of this result is shown in Table 6. When different material was also considered, as shown in Figure 10, the results were similar--amplitude ranges were higher with higher cutting speed. Ranges were overall smaller with MDF, when compared to PTB. The effect of the varying feed rate, as shown in Figure 11, did not seem as clear.