## 2 Materials and Methods
The machining was performed in dry conditions by environmental reasons, but with the application of compressed air directed at the cutting zone. The use of compressed air served to facilitate chip evacuation and to prevent chip adhesion to the turned surface. Preliminary tests revealed that the elevated temperatures generated during the cutting process could cause softened PLA chips to stick to the turned machined surface, affecting the surface finish. The airflow prevented this by removing the chips from the cutting area as they formed. The cutting tool used in the turning operation was a DCMT 11T308-14 IC20 insertIS-CAR Ltd. Tefen, Israel), manufactured by Iscar, and mounted on an SDJCR 2020K11 tool holder(Sandvik Coromant, Sandviken, Suecia). The insert geometry corresponds to a 66\({}^{\circ}\) principal cutting edge angle, which was specifically selected to prevent tool interferences that can occur when reducing the diameter of the workpiece, thereby minimizing the risk of local deformation or dimensional inaccuracies during the turning process. In addition, this tool orientation causes the resulting forces to have a significant component between layers of the FFF-printed material, generating stresses between adjacent layers, which increases the risk of delamination or fracture. This condition is intentionally introduced to evaluate the structural integrity of the material undergoing machining and to assess the feasibility of turning as a post-processing operation for fabricated PLA-CF parts. Other cutting geometry characteristics are shown in Table 2.  
A set of cylindrical turning operations was performed by combining two cutting speeds (\(v_{c}\)) and two feed rates (\(f\)), remaining constant the depth of cut (\(a_{p}\)), whose values can be observed in Table 3. The selected cutting parameters have been defined to explore the machinability of PLA-CF under representative boundary conditions. The cutting speed and feed values were selected based on ranges reported for polymer [42, 43], as well as preliminary tests aimed at ensuring chip formation and structural integrity during cutting. The objective was to assess both low-load and high-demand machining scenarios within the capabilities of workpiece material. A constant depth of cut was maintained to isolate the effects of \(v_{c}\) and \(f\) on thermal, mechanical, and geometric responses. \begin{table}
\begin{tabular}{c c} \hline \hline
**Cutting Tool Geometry** & **Value** \\ \hline Relief angle (\(\alpha\)) & 7\({}^{\circ}\) \\ Cutting edge angle (\(\beta\)) & 66\({}^{\circ}\) \\ Rake angle (\(\gamma\)) & 17\({}^{\circ}\) \\ Major cutting edge angle (\(\kappa_{\tau}\)) & 62.5\({}^{\circ}\) \\ Insert include angle (\(\varepsilon\)) & 55\({}^{\circ}\) \\ Nose radius & 0.8 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Tool geometry data for turning operations. \begin{table}
\begin{tabular}{c c c} \hline \hline \(v_{c}\) **(m/min)** & \(f\) **(mm/rev)** & \(a_{p}\) **(mm)** \\ \hline
50–200 & 0.05–0.20 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Cutting parameter values for turning operations. Each parameter combination was applied to a single specimen. However, since machining is a continuous process, measurements were acquired throughout the entire cutting length and along the resulting surface. This allowed the reproducibility and consistency of the process to be assessed within each test, based on the thermal, mechanical, and geometrical responses observed. Turning operation was carried out along a machined length of 150 mm on the cylindrical surface of the specimen. The machining operation conditions were repeated for each of the combinations of cutting parameters, reducing in each case the final specimen diameter until part failure occurred. This approach provides a better understanding of the mechanical limitations of machining PLA-CF fabricated by FFF as a post-processing method. It is important to notice that all machining tests were performed using the same cutting edge, as no visible tool wear or degradation was observed.