# Cutting Force When Machining Hardened Steel and the Surface Roughness Achieved
### Technological Conditions of Machiting When Measuring with a Kistler Dynamometer  
The machine used for the experiment was the universal spindle lathe SV 18 RD, which is a conventional lathe that has been verified for rigidity. Verification of the machine's accuracy and rigidity was carried out using a certified method as part of preventive maintenance. The machine also has a considerable range of cutting speeds that can be continuously controlled. The spindle speed range is 56-2800 min\({}^{-1}\). The power of the main motor at maximum rpm is 10 kW. The main advantage of this conventional lathe is the added potential for placing the measuring probes of the Kistler dynamometer on the back of the slide. The specific tools used by Dormer Pramet were as follows:  
* Tool holder PCLNL 2525 M 12 in left-hand version;
* Replaceable insert CNGA 120408 S 01020B shown in Figure 2, made of TB310, polycrystalline cubic boron nitride, suitable for use without cutting fluid. One tool was used for the entire series of 12 samples. The insert dimensions and recommended cutting conditions are given in Table 2.  
The cutting conditions are represented the following variables:  
* Cutting speed \(v_{c}\), which depends on the number of revolutions and diameter of the workpiece;
* The feed rate \(f\), which is defined by the movement of the tool per revolution; \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \(r_{\epsilon}\) & \(a_{p}\) & \(f\) & \(v_{\epsilon}\) & \(d\) & \(d_{1}\) & \(l\) & \(s\) \\ \hline
**(mm)** & **(mm)** & **(mm\(\cdot\)rev\({}^{-1}\))** & **(m\(\cdot\)min\({}^{-1}\))** & **(mm)** & **(mm)** & **(mm)** & **(mm)** \\ \hline
0.8 & 0.1–2.7 & 0.02–0.20 & 100–200 & 12.7 & 5.16 & 12.9 & 4.76 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Dimensional specifications of the insert used and range of recommended cutting conditions. Figure 1: Sample of a semi-finished rolling element, left, and a machined sample, right. Figure 2: General dimensions of the insert and toolholder. * The cutting edge width \(a_{p}\), which is determined by the tool's approach to the cutting edge. The geometry of cutting tools is an important factor in turning hard materials. The basic geometry of a cubic boron nitride insert as laid on a horizontal surface as follows:
* Orthogonal face angle \(\gamma_{0}=0^{\circ}\);
* Orthogonal back angle \(\alpha_{0}=0^{\circ}\);
* Orthogonal edge angle \(\beta_{0}=90^{\circ}\). After inserting the insert into the tilted toolholder bed, the working angles of the insert are as follows:
* Orthogonal face angle \(\gamma_{0}=-6^{\circ}\);
* Orthogonal back angle \(\alpha_{0}=6^{\circ}\);
* Blade inclination angle \(\lambda_{8}=-6^{\circ}\);
* Main blade setting angle \(\kappa_{r}=95^{\circ}\);
* Angle of adjustment of the secondary blade \(\kappa_{r}^{\prime}=5^{\circ}\). The ranges of \(f\) and \(a_{p}\) given here are informative; the parameters used in the study provided data to determine the structural equation. One tool was used for the whole series of samples. The complete tool holder, including the inserts used during the experiment, as placed on the probe of the Kistler 9257B dynamometer is shown in Figure 3a. The diagram of the distribution of cutting forces during turning is given in the schematic part of Figure 3b and shows the normal situation when the tool is in front of the axis. In our case, the tool was behind the axis, as shown in Figure 3a, with the actual direction of the forces and a description of the situation given in this Figure. This location is required by the design of the Kistler dynamometer encoder. The direction of the passive force \(F_{p}\) is then reversed. In the last part of Figure 3c, the label of the Kistler 9257B dynamometer is shown with the individual directions of the axes of the cutting resistance against the cutting forces when the dynamometer is placed in the front part of the caliper.