## 3 Experimental Setup
### Experimental Conditions  
Achieving reliable outcomes in experimental research largely depends on selecting suitable system parameters and operating conditions. In this study, three distinct levels were identified for each parameter, including feed rate, spindle speed, coolant temperature, and emulsion concentration. The experimental parameters are summarized in Table 1. Experiments were conducted at coolant temperatures maintained at 15 \({}^{\circ}\)C and 20 \({}^{\circ}\)C when the developed system was active and at ambient temperature when inactive. Coolant emulsions with concentrations of 2.5%, 5%, and 7.5% were tested. Additionally, drilling experiments incorporated three variations for both spindle speed and feed rate. The selection of workpiece materials prioritized those commonly utilized in industrial applications. Manufacturing practices and relevant literature were also referenced when determining drilling parameters. The details of process parameters and the experimental design matrix are provided in Tables 1 and 2, respectively. Figure 5: The experimental setup. The heat recovery system is integrated into the machine tool (vertical machining center, manufactured by Haas Automation, Inc., Oxnard, CA, USA) to carry out the experiments. The test specimen dimensions used in the experiment are shown in Figure 6. For the experiments, 27 prismatic test samples are prepared from AISI 1045 (Eregli Iron and Steel Works Co., Zonguldak, Turkey) manufacturing steel with dimensions of 250 \(\times\) 150 \(\times\) 50 mm. The samples are drilled with a 12 mm diameter HSS drill bit(manufactured by Machine \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Factor**} & \multicolumn{3}{c}{**Level**} \\ \cline{2-5}  & & **a** & **b** & **c** \\ \hline Coolant temperature (\({}^{\circ}\)C) & 15 & 20 & Room temperature \\ \hline Coolant emulsion ratio (\%) & 2.5 & 5 & 7.5 \\ \hline Feed rate (mm/rev) & 0.04 & 0.06 & 0.08 \\ \hline Spindle speed (rpm) & 398 & 531 & 663 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Process parameters. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Test No**} & \multicolumn{2}{c}{**Coolant Set Temperatures (\({}^{\circ}\)C)**} & \multicolumn{2}{c}{**Coolant Emulsion Rates**} & \multicolumn{2}{c}{**Feed Rate (mm/rev)**} & \multicolumn{2}{c}{**Spindle Speed (rev/m)**} \\ \hline \multirow{3}{*}{1} & a & 15 & 2.50 & 0.04 & 398 \\ \cline{2-5}  & b & 20 & 2.50 & 0.04 & 398 \\ \cline{2-5}  & c & Room temperature & 2.50 & 0.04 & 398 \\ \hline \multirow{3}{*}{2} & a & 15 & 2.50 & 0.06 & 531 \\ \cline{2-5}  & b & 20 & 2.50 & 0.06 & 531 \\ \cline{2-5}  & c & Room temperature & 2.50 & 0.06 & 531 \\ \hline \multirow{3}{*}{3} & a & 15 & 2.50 & 0.08 & 663 \\ \cline{2-5}  & b & 20 & 2.50 & 0.08 & 663 \\ \cline{2-5}  & c & Room temperature & 2.50 & 0.08 & 663 \\ \hline \multirow{3}{*}{4} & a & 15 & 5.00 & 0.04 & 531 \\ \cline{2-5}  & c & Room temperature & 5.00 & 0.04 & 531 \\ \hline \multirow{3}{*}{5} & a & 15 & 5.00 & 0.06 & 663 \\ \cline{2-5}  & b & 20 & 5.00 & 0.06 & 663 \\ \cline{2-5}  & c & Room temperature & 5.00 & 0.06 & 663 \\ \hline \multirow{3}{*}{6} & a & 15 & 5.00 & 0.08 & 398 \\ \cline{2-5}  & b & 20 & 5.00 & 0.08 & 398 \\ \cline{2-5}  & c & Room temperature & 5.00 & 0.08 & 398 \\ \hline \multirow{3}{*}{7} & a & 15 & 7.50 & 0.04 & 663 \\ \cline{2-5}  & b & 20 & 7.50 & 0.04 & 663 \\ \cline{2-5}  & c & Room temperature & 7.50 & 0.04 & 663 \\ \hline \multirow{3}{*}{8} & a & 15 & 7.50 & 0.06 & 398 \\ \cline{2-5}  & b & 20 & 7.50 & 0.06 & 398 \\ \cline{2-5}  & c & Room temperature & 7.50 & 0.06 & 398 \\ \hline \multirow{3}{*}{9} & a & 15 & 7.50 & 0.08 & 531 \\ \cline{2-5}  & b & 20 & 7.50 & 0.08 & 531 \\ \cline{2-5}  & c & Room temperature & 7.50 & 0.08 & 531 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental design matrix. Tool Industry (MTE), Krinkkale, Turkey) using the different parameters in Table 1 as 96 holes per part. In total, 2592 holes were drilled throughout the experiments.