# Investigations on Factors Affecting 3D-Printed Holes Dimensional Accuracy and Repeatability
## 3 Results and Discussion
### Results of the Experiment 2  
Table 6 presents the measurement data on the 3D-printed test parts 2 before and after the medical decontamination process, as well as the printing time for each test part. The smallest diameter of a calibration pin that completely passed through a hole with press fit (see also the Supplementary Material) is listed. As an example, in specimen 18, there were three 2.3 mm holes oriented at 5\({}^{\circ}\) (no. 4, 7, 9, Figure 3a) and the 1.883 mm pin passed through all the holes. This type of measurement approach offers information on the diameter values along the entire length of the hole. All the holes were built undersized in the test parts 2, irrespective of the number of shells and layer thickness, which was not the case of some of the holes of the test parts 1, some of which were manufactured oversized. The specimens manufactured with 0.2 mm layer thickness presented more dimensional variability, although for the specimens 19 and 20 the deviations from the nominal value were smaller than for the specimens 17 and 18 which were 3D printed with 0.1 mm layer thickness. The specimen 20 with 0.2 mm layer thickness and three shells was the most accurate. The dimensional repeatability was better for the test parts 3D-printed with 0.1 mm layer thickness, irrespective of the number of shells or hole's axis orientations. Although, in general, the 0.1 mm layer thickness slightly improved the dimensional repeatability, the printing time was double. It should also be mentioned for the surgical drill guides for orthopedic surgery that, where the accuracy is relevant, but not in terms of two significant digits, the process parameters should be set by also considering other criteria, such as printing time or mechanical strength. As mentioned, the results in Table 6 showed that the medical decontamination process produced a larger variability of the holes diameters. If for the 2 mm holes, the diameters have smaller sizes after decontamination, caused by the holes deformation as noticed during the measurement process, for most of the other diameters, the dimensions increased. However, for answering the research question formulated for experiment 2, a quantitative analysis (one-way ANOVA) was conducted. Based on the experimental results, there is no statistically significant difference between the holes' accuracy before and after the part medical decontamination, regardless of the holes' diameters (Table 7). The significance level was 0.05. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Specimen**} & \multirow{2}{*}{\
\begin{tabular}{c} **Hole Axis** \\ **Angle** \\ \end{tabular} } & \multicolumn{2}{c}{**2.3 mm Diameter**} & \multicolumn{2}{c}{**4.5 mm Diameter**} & \multicolumn{2}{c}{**6.5 mm Diameter**} & \multirow{2}{*}{
\begin{tabular}{c} **Printing** \\ **Time** \\ \end{tabular} } \\ \cline{3-3} \cline{5-8}  & & **Before (mm)** & & **After (mm)** & & **Before (mm)** & & **Before (mm)** & **After (mm)** & **Time** \\ \hline \multirow{3}{*}{\(17\)} & 5\({}^{\circ}\) & 2.05 & 2.031 & 4.141 & 4.134 & 6.212 & 6.287 & \\  & 10\({}^{\circ}\) & 2.05 & 2.031 & 4.141 & 4.187 & 6.212 & 6.265 & \\  & 15\({}^{\circ}\) & 2.05 & 2.031 & 4.141 & 4.334 & 6.212 & 6.287 & \\ \hline \multirow{3}{*}{\(18\)} & 5\({}^{\circ}\) & 1.833 & 1.833 & 4.141 & 4.130 & 6.212 & 5.997 & \\  & 10\({}^{\circ}\) & 1.833 & 1.827 & 4.141 & 4.315 & 6.212 & 6.203 & \\  & 15\({}^{\circ}\) & 1.833 & 1.827 & 4.141 & 4.320 & 6.036 & 6.202 & \\ \hline \multirow{3}{*}{\(19\)} & 5\({}^{\circ}\) & 1.883 & 1.827 & 4.260 & 4.130 & 6.212 & 6.060 & \\  & 10\({}^{\circ}\) & 1.883 & 1.827 & 4.216 & 4.220 & 6.212 & 6.253 & \\ \cline{1-1}  & 15\({}^{\circ}\) & 1.883 & 1.827 & 4.141 & 4.230 & 6.065 & 6.253 & \\ \hline \multirow{3}{*}{\(20\)} & 5\({}^{\circ}\) & 2.05 & 2.043 & 4.350 & 4.341 & 6.350 & 6.208 & \\  & 10\({}^{\circ}\) & 2.05 & 2.043 & 4.350 & 4.344 & 6.220 & 6.281 & \\ \cline{1-1}  & 15\({}^{\circ}\) & 2.05 & 2.088 & 4.295 & 4.344 & 6.212 & 6.360 & \\ \hline \hline \end{tabular}
\end{table}