## 2 Methodology and Materials
### Methodology
Roughness values were taken at the entrance and exit of each hole in each of the three plates that conform the multimaterial, with a total of eight experimental re-drillings, and six _Ra_ (\(\upmu\)m) measurements \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Factors** & **Levels (Code)** & **Levels (Values)** & **Type** \\ \hline Depth of cut, \(d\), (mm) & _d1_ & 0.5 & Quantitative \\ Feed rate, \(f\) (mm/rev) & _a1_, _a2_ & 0.05/0.1 & Quantitative \\ Spindle speed \(N\) (rpm) & _N1_, _N2_ & 500/1200 & Quantitative \\ Type of cooling system, \(C\) & _CCA_, _Dry_ & _CI/C2_ & Qualitative \\ Location Regarding Insert, _LRI_ & _Mg1/Al2/Mg3_ & _LRII_, _LRI2_, _LRI3_ & Qualitative \\ Location Regarding Specim, _LRS_ & Drill hole: entry/exit & _LRS1_, _LRS2_ & Qualitative \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Factors and levels. per hole, providing a total of 48 measurements that can be seen in Table 2. Roughness measurements were taken using a Mitutoyo Surftest SJ 401 which has a measurement range of 800 \(\upmu\)m and a resolution of 0.000125 \(\upmu\)m and using the ISO-1997 standard. The areas where the roughness measurements are taken regarding the location of the plate within the hybrid compound, _LRI_ factor, are _LRI1_ (Mg1), _LRI2_ (Al2), and _LRI3_ (Mg3), and the areas where roughness measurements are taken regarding its location within each hole, _LRS_ factor, are _LRS1_ (entrance of the hole) and _LRS2_ (exit of the hole). Figure 1 shows a representation of the multimaterial component tested indicating the LRI factors on the left and the LRS factors on the right together with the drilling direction. Afterwards, machining tests were carried out. Before performing the re-drilling tests, protocols were established both for the cutting parameters and the collection of the response variable data. Subsequently, test specimens, tools, CCA equipment, and the machining center were prepared, and the selected cutting conditions introduced. Then, the machining operations were carried out. Finally, photographs were taken, and videos recorded, for subsequent analysis. Subsequently, the response variable was measured. Specifically, the surface roughness was selected and analyzed as the Arithmetical Mean Roughness, _Ra_ (\(\upmu\)m). Once the data were collected, a statistical analysis was carried out. The variability of the _Ra_ (\(\upmu\)m) was modeled using Analysis of Variance (ANOVA), the factors, and interactions between them with an influence on surface roughness were identified. Finally, the results were statistically analyzed, and conclusions drawn. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Test No.** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** \\ \hline  & _LRI1/LRS1_ & _LRI1/LRS1_ & _LRI1/LRS1_ & _LRI1/LRS1_ & _LRI1/LRS1_ & _LRI1/LRS1_ & _LRI1/LRS1_ & _LRI1/LRS1_ \\  & _LRI1/LRS2_ & _LRI1/LRS2_ & _LRI1/LRS2_ & _LRI1/LRS2_ & _LRI1/LRS2_ & _LRI1/LRS2_ & _LRI1/LRS2_ & _LRI1/LRS2_ \\ _LRI/LRS_ & _LRI2/LRS1_ & _LRI2/LRS1_ & _LRI2/LRS1_ & _LRI2/LRS1_ & _LRI2/LRS1_ & _LRI2/LRS1_ & _LRI2/LRS1_ \\  & _LRI2/LRS2_ & _LRI2/LRS2_ & _LRI2/LRS2_ & _LRI2/LRS2_ & _LRI2/LRS2_ & _LRI2/LRS2_ & _LRI2/LRS2_ \\  & _LRI3/LRS1_ & _LRI3/LRS1_ & _LRI3/LRS1_ & _LRI3/LRS1_ & _LRI3/LRS1_ & _LRI3/LRS1_ & _LRI3/LRS1_ & _LRI3/LRS1_ \\  & _LRI3/LRS2_ & _LRI3/LRS2_ & _LRI3/LRS2_ & _LRI3/LRS2_ & _LRI3/LRS2_ & _LRI3/LRS2_ & _LRI3/LRS2_ & _LRI3/LRS2_ \\ C & _CL_ & _CL_ & _CL_ & _CL_ & _CL_ & _CL_ & _CL_ & _CL_ & _CL_ & _CL_ & _CL_ \\ \(f\) (_mm/rev_) & _f1_ & _f1_ & _f2_ & _f2_ & _f1_ & _f1_ & _f2_ & _f2_ \\ \(N\) (_rpm_) & _N1_ & _N2_ & _N1_ & _N2_ & _N1_ & _N2_ & _N1_ & _N2_ & _N1_ & _N2_ \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mg-Al-Mg specimen experimental design: product of a full factorial 2 and a block of two factors. Figure 1: Detail of the position of the roughness measurements inside each Mg-Al-Mg specimen; (**a**) Location Regarding Insert, _LRI_; (**b**) Location Regarding Specim, _LRS_.