# Investigations on Factors Affecting 3D-Printed Holes Dimensional Accuracy and Repeatability
## 2 Materials and Methods
### Experiment 2: Surgical Drill Guide Holes' Dimensional Accuracy and Repeatability  
The second test part mimicked an orthopedic surgical drill guide included three rows of cylinders with axes oriented at 5\({}^{\circ}\), 10\({}^{\circ}\), and 15\({}^{\circ}\) relative to the horizontal plane, and with holes of 2.3 mm (for the K-wires), 4.5 mm, and 6.5 mm diameter (Figure 3a). Such guides are used by the orthopedic surgeons to pre-drill the screws holes before performing an osteotomy [24], the range of diameters selected for this test part being typical for such an application. These parts were 3D-printed in the manufacturing site 2 which provided the best dimensional accuracy according to the outcomes of experiment 1.  
As the results of the experiment 1 also offered information on the less significant influence factor (meaning the printing speed), the levels for this factor were removed in experiment 2, and four specimens were 3D-printed by setting two values for the layer thickness and two values for number of shells (Table 3). As the layer thickness was found as correlating with the holes' diameter accuracy, a smaller layer thickness (0.1 mm) was added as a level in the design of experiments. At the same time, the selected values were in accordance with previous research on MEX settings to provide the best sealing against disinfectants infiltration [8]. For the test part 2, the infill density was set to 70%, a value that provides the required strength for the drill guiding cylinders [25]. The printing speed was set to 50 mm/s. This experiment purpose was to evaluate the combined influence of process parameter settings and medical decontamination process on the dimensional accuracy and repeatability of the test part with inclined holes.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Manufacturing Site** & **3D Printer** & **Slicer** & **Material** & **No. of Test Parts** \\ \hline
1 & Prusa Replica & Prusa & PLA 1 & 12 \\
2 & Original Prusa i3 & Prusa & PLA 1 & 1 (specimen 13) \\
3 & Creality CR10 & Cura & PLA 1 & 1 (specimen 14) \\
4 & Ender 3 & Simplify3d & PLA 2 & 1 (specimen 15) \\
5 & Mojo & Print Wizard & ABS & 1 (specimen 16) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Test parts built in different manufacturing sites.  
Figure 3: Test part 2 with holes of 2.3 mm, 4.5 mm, and 6.5 mm in diameter (holes axes angles of 5\({}^{\circ}\), 10\({}^{\circ}\) and 15\({}^{\circ}\)): (**a**) virtual model, (**b**) pass-no pass test on the physical model.  
The medical decontamination process consisted in soaking the test parts into Anisoyme XL3 (Ecolab, Saint Paul, MN, USA) for 15 min, followed by rinsing with water and immersion in Sekusept (Laboratories Lezennes, Lezennes, France, Fr) for another 15 min, followed by rinsing with water, drying, and hydrogen peroxide gas plasma sterilization using Sterrad equipment for 45 min cycle program at 134 \({}^{\circ}\)C and 0.223 MPa (2.2 atm) [8]. Only one cycle of decontamination was set as the 3D-printed surgical guides are patient-customized, and therefore they are used one time for one patient.  
For measuring the holes diameters, sets of calibration pin gauges with increments of 0.001 mm (Figure 3b) were used before and after the medical decontamination.