## 3 Results and Discussion
### Dimensional Accuracy  
Three different values of structure length (5, 10, and 20 mm) were tested in the X and Y directions. The results in terms of the dimensional error% were very similar for all lengths in both the X and the Y direction, and that is why only one value (for 10 mm) in the X direction is presented and discussed. The developed quadratic regression model for the percentage error of dimensional accuracy for 10 mm in the x-direction (termed: \(Error_{X}\)\([\%]\) in this paper for abbreviation) is shown in Equation (3). The model originally presents 21 terms for the 5 process parameters that were studied in this work. Nevertheless, in the following equations, all factors with coefficient less than 0.001 were ignored. \[ \begin{array}{l}Error_{X}\ [\%]=0.773+0.112*x_{1}+0.451*x_{2}+0.396*x_{3}+0.275*x_ {4}-0.174*x_{5}-\\ 0.019*x_{1}x_{2}-0.068*x_{1}x_{3}-0.144*x_{1}x_{4}-0.215*x_{1}x_{5}-0.084*x_{2} x_{3}-0.235*x_{2}x_{5}+\\ 0.358*x_{3}x_{4}+0.009*x_{3}x_{5}+0.026*x_{4}x_{5}-0.279*x_{2}{}^{2}+0.32*x_{3} {}^{2}-0.34*x_{4}{}^{2}-0.029*x_{5}{}^{2}\end{array}  \tag{3}\]  
where \"x\({}_{1}\)\" is the normalized value for infill percentage, \"x\({}_{2}\)\" refers to the normalized value of layer thickness, \"x\({}_{3}\)\" denotes the normalized value of printing speed, \"x\({}_{4}\)\" is the normalized value for printing temperature, and \"x\({}_{5}\)\" represents the normalized value for the surface inclination angle. ANOVA was used to identify the three most significant parameters: first was printing speed (\(p\)-value = 0.00023); second was layer thickness (\(p\)-value = 0.00206), and third was printing temperature (\(p\)-value = 0.0171). Looking at the plot, see Figure 6, and respective regression model in Equation (3), it is evident that with either increasing layer thickness or printing speed, the error% rises quite sharply. It is assumed that thicker layers contribute to a greater inaccuracy as they tend to spread out more after extrusion. Such a possibility could be reduced by lowering the printing temperature, which could improve the accuracy, since a lower temperature will mean a higher value for the viscosity which would reduce the spread of the PLA and enhance the ability to maintain the desired dimensions of the printed structure. Printing temperature was found to have an effect on the obtainable dimensional accuracy error%, and this effect was attributed to change of viscosity of the melted material. Faster printing speeds increased inaccuracy, which could be attributed to lower accuracy during extrusion and placement of the filament, since it is tauter and has less time to connect to the previous layer. These observations go in hand with the results of ANOVA. Higher infill percentages foster inaccuracy, due to possible widening of the dense raster inside the build part. Surface inclination angle was found to have no significant effect on the obtainable dimensional accuracy of the printed part. The predicted interaction effects, illustrated in Figure 7, show thinner layers, and lower printing speeds lead to negative errors, which means the built part is smaller than the CAD design, these can be attributed to greater contraction of the part. In contrast, thicker layers and higher printing temperatures contribute to a greater positive error, possibly due to the filament spreading outwards. In addition, higher printing speeds and temperatures give greater positive error, as the material is more liquid and under greater tension and is, therefore, more stretched. The results of this study agree with the findings of [PERSON] et al. [34] that printing speed is the most effective process parameter determining dimensional accuracy. [PERSON] et al. [30] have affirmed the negative influence of high printing temperatures on dimensional accuracy. The results of [PERSON] et al. [35] agree only in part with this study, since they recommended greater layer thickness to reduce percentage deviation.