## 2 Materials and Methods
### Experimental Design and Measurements  
The total number of experiments was generated based on the full factorial design of the three parameters and their three levels, in addition to the 12 testing experiments. All 39 experimental results are shown in Table 2, including the surface roughness and the tool-tip temperature. \begin{table}
\begin{tabular}{c c} \hline \hline
**Setting** & **Value** \\ \hline Printing Nozzle temperature & 255 \({}^{\circ}\)C \\ Plate temperature & 70 \({}^{\circ}\)C \\ Filament & 1.75 mm \\ Printing Nozzle diameter & 0.6 mm \\ Layer & 0.2 mm \\ Printing speed & 40 mm/s \\ Flow & 100\% \\ Shell thickness & 3 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Settings for fabricating the workpieces using the FFF method. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Experiment** & _Vc_ & \(f\) & _ap_ & _Ra_ & \(T\) \\  & **No.** & **(m/min)** & **(mm/rev)** & **(mm)** & **(\(\mu\)m)** & **(\({}^{\circ}\)C)** \\ \hline \multirow{8}{*}{**PETG**} & 1 & 115 & 0.05 & 0.50 & 1.823 & 37.9 \\  & 2 & 115 & 0.05 & 1.25 & 2.198 & 40.1 \\  & 3 & 115 & 0.05 & 2.00 & 2.301 & 43.0 \\  & 4 & 115 & 0.08 & 0.50 & 2.009 & 47.2 \\  & 5 & 115 & 0.08 & 1.25 & 2.580 & 48.0 \\  & 6 & 115 & 0.08 & 2.00 & 2.308 & 49.9 \\  & 7 & 115 & 0.11 & 0.50 & 2.566 & 54.4 \\  & 8 & 115 & 0.11 & 1.25 & 3.090 & 55.1 \\  & 9 & 115 & 0.11 & 2.00 & 3.362 & 57.0 \\  & 10 & 200 & 0.05 & 0.50 & 1.762 & 49.8 \\  & 11 & 200 & 0.05 & 1.25 & 1.989 & 52.3 \\  & 12 & 200 & 0.05 & 2.00 & 2.253 & 55.9 \\  & 13 & 200 & 0.08 & 0.50 & 2.020 & 60.0 \\  & 14 & 200 & 0.08 & 1.25 & 2.744 & 62.3 \\  & 15 & 200 & 0.08 & 2.00 & 2.466 & 69.0 \\  & 16 & 200 & 0.11 & 0.50 & 2.788 & 70.3 \\  & 17 & 200 & 0.11 & 1.25 & 3.067 & 70.5 \\  & 18 & 200 & 0.11 & 2.00 & 3.255 & 72.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The experimental results according to the training and testing data. Figure 2: The geometry of the specimens (**a**) and sample 3D-printed workpieces (**b**). The normal probability plots were plotted to assess the data point distribution, as shown in Figure 3, by utilizing the Anderson-Darling test [35] and setting the confidence level to 95%. By observing both plots, it is shown that the data points are very close to the line that represents the distribution. It is noted that Figure 3a illustrates the probability plot for \(Ra\) and Figure 3b for \(T\). The pattern of the data points across the straight line suggests that they follow the normal distribution. In addition, it is shown that none of the points fall outside the confidence bands, with the exception of one or two points that intersect the bands. Finally, the points of both models are tightly clustered around the distribution line, indicating that both \(Ra\) and \(T\) measurements have a consistent variance, a fact that supports the normality assumption. \begin{table}
\begin{tabular}{r r r r r r r} \hline  & **Experiment** & \(Vc\) & \(f\) & \(ap\) & \(Ra\) & \(T\) \\  & **No.** & **(m/min)** & **(mm/rev)** & **(mm)** & **(\(\upmu\))** & **(\({}^{\circ}\)C)** \\ \hline  & 19 & 285 & 0.05 & 0.50 & 2.121 & 51.7 \\  & 20 & 285 & 0.05 & 1.25 & 2.262 & 58.7 \\  & 21 & 285 & 0.05 & 2.00 & 2.453 & 63.5 \\  & 22 & 285 & 0.08 & 0.50 & 2.429 & 66.9 \\  & 23 & 285 & 0.08 & 1.25 & 3.288 & 72.8 \\  & 24 & 285 & 0.08 & 2.00 & 2.616 & 74.4 \\  & 25 & 285 & 0.11 & 0.50 & 3.199 & 76.2 \\  & 26 & 285 & 0.11 & 1.25 & 3.566 & 77.1 \\  & 27 & 285 & 0.11 & 2.00 & 3.890 & 84.6 \\ \hline  & 28 & 150 & 0.06 & 0.75 & 1.850 & 45.2 \\  & 29 & 175 & 0.09 & 1.50 & 2.893 & 56.3 \\  & 30 & 225 & 0.07 & 1.75 & 2.295 & 69.7 \\  & 31 & 250 & 0.06 & 1.00 & 2.237 & 65.6 \\  & 32 & 130 & 0.07 & 1.50 & 2.329 & 49.6 \\  & 33 & 185 & 0.10 & 0.90 & 2.856 & 65.4 \\  & 34 & 260 & 0.07 & 1.30 & 2.932 & 68.6 \\  & 35 & 145 & 0.09 & 0.60 & 2.253 & 58.8 \\  & 36 & 210 & 0.06 & 1.60 & 2.286 & 55.7 \\  & 37 & 270 & 0.09 & 0.80 & 2.821 & 70.1 \\  & 38 & 190 & 0.07 & 1.10 & 2.478 & 58.3 \\  & 39 & 240 & 0.10 & 1.40 & 3.357 & 75.2 \\ \hline \end{tabular}
\end{table}