## 2 Experimental
### Center-of-Rotation Error Compensation
Error along the \(X\) axis:  
\[\Delta X=-D_{4}=-d_{x_{c}}+cos[\theta_{c}]d_{x_{c}}+sin[\theta_{c}]d_{y_{c}} \tag{4}\]  
Error along the \(Y\) axis:  
\[\Delta Y=D_{3}=-sin[\theta_{c}]d_{x_{c}}-d_{y_{c}}+cos[\theta_{c}]d_{y_{c}} \tag{5}\]  
The measured differences of side walls \(D_{3}\) and \(D_{4}\) and two known angles of rotation, \(90^{\circ}\) and \(180^{\circ}\), were substituted into (4) and (5), where \(D_{3}\) and \(D_{4}\) had identical physical meanings to \(\Delta X\) and \(\Delta Y\)), to determine the center-of-rotation errors along the \(C\) axis, \(d_{x_{c}}\) and \(d_{y_{c}}\). In the experiment on center-of-rotation errors along the \(C\) axis, a 5 mm end mill was used in combination with varying angles of rotation of the table along the \(C\) axis (\(0^{\circ}\), \(90^{\circ}\), and \(180^{\circ}\)) to cut a groove on the workpiece surface. If no center-of-rotation error occurred along the \(C\) axis, the cut groove would not form \"step difference,\" as shown in Figure 5a,b. Subsequently, 3D-Probe was used to measure the differences in sidewalls of the cut groove (measurement faces had to be on the same side), and groove sidewalls cut at the rotation angle of \(0^{\circ}\) were used as the baseline (no error at \(0^{\circ}\) of  
Figure 4: Center-of-rotation errors along the \(C\) axis. Figure 3: Cut groove and depth of cut difference measurements of rotation along the \(A\) axis. rotation). The groove depth values at 90\({}^{\circ}\) and 180\({}^{\circ}\) were measured (\(D_{3}\) and \(D_{4}\), respectively), as shown in Figure 5c. After the experiments to identify center-of-rotation error values along the \(A\) and \(C\) axes (\(d_{y_{A}}\), \(d_{z_{A}}\), \(d_{x_{e}}\), and \(d_{y_{e}}\)), the point coordinates P(\(X_{0}\), \(Y_{0}\), \(Z_{0}\)) in a numerical control (NC) program was rotated against the origins on the \(XY\) and \(YZ\) planes (the angles of rotation were calculated according to steps in corresponding sections) to obtain the machining point Q(\(X_{1}\), \(Y_{1}\), \(Z_{1}\)). Subsequently, the machining point Q(\(X_{1}\), \(Y_{1}\), \(Z_{1}\)) was counter-rotated against the origin (\(d_{x_{e}}\), \(d_{y_{e}}\)) on the \(XY\) plane and the origin (\(d_{y_{A}}\), \(d_{z_{A}}\)) on the YZ plane to obtain the compensated NC point coordinates R(\(X_{2}\), \(Y_{2}\), \(Z_{2}\)), which was the correct machining point. The coordinates of the compensated R(\(X_{2}\), \(Y_{2}\), \(Z_{2}\)) were calculated using (6)-(8):  
\[X_{2}=X_{0}-(-1+cos[\theta_{c}])d_{x_{e}}+sin[\theta_{c}]((-1+cos[\theta_{A}] )d_{y_{A}}+d_{y_{e}}-sin[\theta_{A}]d_{z_{A}}) \tag{6}\]  
\[\Delta Z=-sin[\theta_{A}]d_{y_{A}}-d_{z_{A}}+cos[\theta_{A}]d_{z_{A}} \tag{3}\]0  
\[\Delta Z=-sin[\theta_{A}]d_{y_{A}}-d_{z_{A}}+cos[\theta_{A}]d_{z_{A}} \tag{3}\]1  
Cutting Path Planning in Five-Axis Computer-Aided Manufacturing (CAM) of Stents and Actual Stent Machining  
The degradable PLA biomedical stent developed in this study is compact in size, has relatively low strength, and a glass transition temperature of approximately 60 \({}^{\circ}\)C; thus, it has numerous machining constraints. This study used a CAM software package (PowerMILL) as well as applied layered spiral machining methods and results of the cutting parameter optimization experiment to plan the cutting parameters and paths of cutting tools. The edge of the cutting tool was used to cut downward layer by layer along the stent profile. The depth of cut for each layer was 0.03 mm (total depth of cut = 0.36 mm), as shown in Figure 6a. In the axial control of the cutting tool, the tool axis was defined to always point to the center of the cylinder during machining. Figure 6b illustrates a simulation of layered spiral machining. Next, fillet machining of the vertical edge of stents was performed to form a round corner of a quarter-round with a radius of 0.1 mm. The round corner was produced using layered spiral machining to perform 12 cuts along the arc length (0.157 mm), with the spacing of each cut being 0.0134 mm, as shown in Figure 6c.