## 3 Results and Discussion  
### Analysis of Results for the Computation of the Prediction Model  
According to the 3-level plan (Table 6), nine grooves were milled on a sample of the same material, when changing the step and the engagement angle. The dynamometer was placed underneath the workpiece, and the cutting forces were measured in the XYZ system, with the milling cutter performing a motion related to the mathematical definition of trochoid, as shown in Figures 3 and 5. The orientation of the tool relative to the reference system changed depending on the movement, which resulted in a change in the size of the cutting force components (projected into individual axes). At the same time, in the second part of the semicircle, the milling cutter was out of the engagement, which resulted in a \"zero\" load in the course of the components of the total cutting force. Based on the calculated path, the tool came into the engagement, which resulted in a change in the cutting force \(\mathrm{F_{f}}\) (in the \(x\) axis's direction). As the tool moved along the trochoid radius \(\mathrm{R_{p}}\), the force increased. As the tool shifted more in the \(y\) axis, the force component \(\mathrm{F_{fn}}\) grew and the component \(\mathrm{F_{f}}\) tended to decrease. The size of the component \(\mathrm{F_{p}}\) reflected the entire toolpath in engagement. Research of cutting force, or of cutting force components realized by several experts [11; 20; 23; 34; 35; 36] in the previous period, was focused mainly on the determination of the impact of tool movement on its load; the creation of mechanistic models; and, last but not least, identification of other impacts, such as machining vibrations. The detected dependencies make it possible to get an accurate idea of the current tool load. These factors were also taken into account when setting the dynamometer sensing frequency to identify the rotation of the tool and the influence of the load on the individual cutting edges of the tool in contact with the material (in engagement--in our case four teeth to four flutes) clearly. Since our research was focused on analysing the impacts of trochoid parameters on the overall tool load, the analysis was not performed using a chatter model, but through local toolmaking peaks for the individual tool passes and average values for these peaks. The data obtained from the development of the total cutting force components, as shown in Figure 9, served as the basis.  
These graphical outputs do not provide an overview of the trends of the investigated influences at a glance, because the resulting machining force cannot be directly measured; not even its active component can be directly measured. Only rectangular projections of the active and passive force components into the coordinate axes can be directly and precisely measured with the dynamometer. The active force of the total machining force can then be measured indirectly; i.e., it must be evaluated in each partial measurement as the vector sum of the components of the forces \(F_{f}\) and \(F_{fn}\). The total machining force \(F\) can also be measured indirectly; i.e., it can be evaluated in each partial measurement as the vector sum of the components of the forces \(F_{a}\), \(F_{p}\) (Table 7).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Maximum Machining Power \(F_{max}\)**} & \multicolumn{4}{c}{**Engagement Angle \(\alpha\) (\({}^{\circ}\))**} \\ \cline{2-5}  & \(\mathbf{10}^{\circ}\) & \(\mathbf{20}^{\circ}\) & \(\mathbf{30}^{\circ}\) \\ \hline \multirow{3}{*}{Step \(s\) [mm]} & 0.2 mm & 1159 & 1901 & 2658 \\  & 0.6 mm & 1933 & 2867 & 3792 \\ \cline{1-1}  & 1.0 mm & 1548 & 2391 & 3042 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Indirectly measured maximum machining force \(F_{max}\) by the vector sum of experimentally measured maximum force components.