## 2 Materials and Methods  
### Experimental Setup  
The turning tests were carried out in a controlled dry-cutting environment using a CNC INDEX GU600 lathe; it has a spindle speed range between 0 and 6000 rpm, a maximum diameter of 350 mm, and a maximum length of the workpiece of 600 mm, with a 15 KW motor drive. The experimental setup is shown in Figure 1. The experiments utilized high-performance cemented ISO P-grade carbide inserts (SANDVIK TNMG160408 and SANDVIK TNMG160404) to achieve precise cuts on 90 MnCrV7 steel workpieces. The dimensions of the workpiece were 30 mm diameter and 60 mm length, with a cutting length of 40 mm, as illustrated in Figure 1. The measured chemical composition of 90 MnCrV7 is shown in Table 1. The chemical composition analysis was conducted in accordance with the SRPS C.A1.011 (2004) standard [30], using the OES iSpark 8860 device manufactured by ARL Thermo Fisher.  
The cutting parameters selected for the turning process are cutting speed (\(v_{c}\)), feed rate (\(f\)), depth of cut (\(a_{p}\)), and insert radius (\(r_{i}\)). These four selected input parameters were varied at different levels, as shown in Table 2. The levels of input parameters were chosen to correspond to the intermediate and final machining with the cutting tool used in machining the 90 MnCrV7 material. Based on these input values, 120 different samples were cut, and surface roughness (\(R_{a}\)), main cutting force (\(F_{c}\)), passive force (\(F_{p}\)), and feed force (\(F_{f}\)) were measured for both types of inserts.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**C (\%)** & **Mn (\%)** & **Si (\%)** & **P (\%)** & **S (\%)** & **Cr (\%)** & **Ni (\%)** & **Cu (\%)** & **AI (\%)** & **Co (\%)** & **V (\%)** \\ \hline
0.874 & 1.831 & 0.231 & 0.012 & 0.001 & 0.296 & 0.306 & 0.264 & 0.002 & 0.007 & 0.068 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The chemical composition of 90 MnCrV7.  
Figure 1: Experimental setup.  
To ensure stability during machining and reduce potential clamping-related errors and vibrations, each workpiece was pre-processed and securely clamped into soft jaws precisely machined to fit its diameter. The cutting tools were replaced after every ten workpieces to maintain consistent performance, minimize the variability associated with cutting tool wear, and ensure uniform cutting of each workpiece. A customized data acquisition system was developed in MATLAB R2023b to simultaneously monitor and process the signals for cutting forces (\(F_{c}\), \(F_{p}\), \(F_{f}\)). This system included a Kistler 9527A dynamometer attached to the tool holder for force measurement, which helps divide the cutting forces in the three Cartesian directions (x, y, z), as depicted in Figure 1. The dynamometer was connected to a Kistler 5001 signal conditioner. Cutting force signals were collected at a frequency of 4 kHz using an NI PCI 6281 card to ensure accurate and high-resolution data capture for the parameters.  
Surface roughness was characterized using the average roughness of the assessed profile (\(R_{a}\)), measured with a Mitutoyo surftest SJ-210 device. The cut-off length, which defines the segment of the surface profile analyzed to filter out high-frequency noise, was set at 2.5 mm. An evaluation length of 12.5 mm, corresponding to five consecutive cut-off segments, was used to ensure an accurate and representative surface roughness measurement.