## 2 Materials and Methods  
Medium density fiberboards cut to 500 \(\times\) 300 \(\times\) 18 mm with weight 1960 g were used as specimens. The density of these specimens was 720-740 kg\(\cdot\)m\({}^{-3}\). Particleboards of the same dimensions were added as reference specimens. The density of particleboards given by the manufacturer was 600-640 kg\(\cdot\)m\({}^{-3}\) (deciduous 10%, coniferous 90%), and urea formaldehyde glue with paraffin admixture was used; both originated from Kronospan Ltd., Zvolen, Slovakia. The manufacturer declared that the material complied with the EN 14,322 standard, EN 312-2, and emission class E1 (EN ISO 12460-5) [49; 50; 51]. A measurement was conducted on a 5-axis CNC machining center SCM Tech Z5 (Figure 1), in laboratories of Technical University in Zvolen. Table 1 provides the basic technical-technological parameters given by the manufacturer. Figure 1: CNC machining center SCM Tech Z5. Vibration was measured by PicoScope with MEMS accelerometer TA143 [52] with parameters in Table 2.  
Specimens were clamped to four pneumatic grippers, each with surface 120 \(\times\) 120 mm and clamping force 16 kg/m\({}^{2}\) (Figure 2). Each cut had a depth of 19 mm, and so, the whole thickness of the material was machined in one run. To emulate the conditions of nesting milling, a tool trajectory cut through the middle of specimen. The spiral and razor cutter shown in Figure 3 were used as tools, with parameters summed in Table 3.  
Varying feed rate of 2, 6, 10 m\(\cdot\)min\({}^{-1}\) was used, with spindle rotations 10,000 and 20,000 min\({}^{-1}\). Cutting was repeated 3 times for each parameter. Both experimental layout and cutting parameters are shown in Figure 4 and Table 4 [53]. As seen in Figures 2 and 4, accelerometer probes were attached onto pneumatic grippers. To select placement location, multiple tests were conducted with probes placed on each gripper. An example of a result with spindle revolutions of 20,000 min\({}^{-1}\) and feed rate of 6 m\(\cdot\)min\({}^{-1}\) is shown in Figure 5.  
Although cutting parameters were the same, the placement of accelerometer had a visible impact. Grippers G1 and G4 had a larger peak in the beginning of cutting, as they \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{CNC Machining Center SCM Tech Z5 technical parameters} \\ \hline Useful desktop (mm) & X = 3050, Y = 1300, Z = 3000 \\ Speed in \(x\) axis (m\(\cdot\)min\({}^{-1}\)) & 0 \(\div\) 70 \\ Speed in \(y\) axis (m\(\cdot\)min\({}^{-1}\)) & 0 \(\div\) 40 \\ Speed in \(z\) axis (m\(\cdot\)min\({}^{-1}\)) & 0 \(\div\) 15 \\ Vector rate (m\(\cdot\)min\({}^{-1}\)) & 0 \(\div\) 83 \\ \hline \hline \multicolumn{2}{c}{Technical Parameters of the Electric Spindle with HSK F63 Connection} \\ \hline Rotation in C axis & 640\({}^{\circ}\) \\ Rotation in B axis & 320\({}^{\circ}\) \\ Revolutions (min\({}^{-1}\)) & 600 \(\div\) 24000 \\ Electric power (kW) & 11 \\ Maximum tool dimensions (mm) & D = 160, L = 180 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: CNC machining center SCM Tech Z5 technical parameters. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Maximum measurable acceleration & \(\pm\)5 g \\ Output & 0–2 V DC \\ Output scaling & 99 to 122 mV\(\cdot\)g\({}^{-1}\) \\
0 g output & 0.85 to 1.15 V \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Basic parameters of accelerometer TA143. Figure 2: Measurement assembly. (**a**) Pneumatic grippers (G1–G4), (**b**) magnetic attachment of accelerometer (1), (**c**) NVH kit with PicoScope. were closer to the start of tool path. However, there was still a big difference, due to tool rotation. On gripper G1 and G2, vibrations were caused by conventional milling, while grippers G3 and G4 side were experiencing climb milling. Another useful fact was that vibrations in \(y\) axis never showed as maximum in measurement. Therefore, it was concluded that four channels of accelerometer were used to simultaneously measure x and z axes of two grippers.