## 2 Materials and Methods
### Experimental Procedure
#### 2.3.2 Main Study: Sintering Time, Sand Percentage, and Position Inside the Crucible  
In the main study of this research, a total of 14 batches with four prismatic specimens were produced, with each batch representing a process parameter under study. Specimens were printed in both rectangular and cylindrical crucibles, which implied different build directions, horizontal and vertical, respectively. Note that the effect of the position of each specimen in the crucible was also a variable under study, namely, in the horizontally built specimens, since the weight on top of specimens and lateral clearance could influence the sintering stage. In the first eight batches, glass microspheres were used as the build powder, and the hold time of a sintering temperature of 750 \({}^{\circ}\)C was tested, with values varying between 1, 2.5, 4, and 8 h. In the remaining six batches, specimens were produced at a sintering temperature of 750 \({}^{\circ}\)C and a hold time of 1 h. The build powder of these six batches had not only glass but a percentage of sand mixed with it, varying between the values of 20%, 40%, and 60% in weight. To identify each batch of specimens, a labelling system consisting of a number or percentage value and one letter is detailed in Table 2. The letter is related to the primary study variable, i.e., the orientation of the specimens. The letter \"h\" represents horizontally printed specimens, and the letter \"v\" represents vertically printed specimens. The number or percentage was related to a secondary study variable, i.e., hold time (\(\Delta_{hold}\)) or sand percentage in weight (%\({}_{sand}\)). To assess the relative shrinkage of produced parts, all three dimensions of each specimen (length, width, and thickness) were measured using a digital caliper, in three different sections along the specimen's length. The locations of these sections were maintained throughout measurements, i.e., always on the same level of altitude in vertical specimens or longitude in horizontal specimens. The volume of the prismatic specimens was computed using the average of all measurements taken in each specimen, and a ratio between theoretical and experimental volume values was used to compute shrinkage. Warpage was evaluated mostly from a visual and qualitative perspective. The flexural property assessment was conducted on a Universal Testing Machine Instron 5566 with a 500 N load cell and a crosshead speed of 1 mm/min. The transverse rupture strength (\(\sigma_{TRS}\)), flexural strain at rupture (\(\epsilon_{r}\)), and modulus of elasticity in bending (\(E_{Bend}\)) were computed using Equations (1)-(3). \[\sigma_{TRS}=\frac{3P_{r}a}{2 bt^{2}}\ \ [\text{MPa}] \tag{1}\]  
\[\epsilon_{r}=\frac{6\delta_{r}t}{a^{2}} \tag{2}\]  
\[E_{Bend}=\frac{a^{3}k}{4 bt^{3}}\times 10^{-3}\ \ [\text{GPa}] \tag{3}\]  
where \(P_{r}\) is the breaking load; \(a\) is the distance between supports, the span (44 mm); and \(t\) and \(b\) are the experimentally measured values of thickness and width, respectively. In Equation (3), \(k\) is the flexural stiffness, which is the initial slope of the load deflection curve, obtained with the graphical method. After the flexural tests, four vertically printed specimens, one for each sintering holding time, and two horizontally printed specimens, with two different hold times, were selected for the microhardness tests. Hardness Vickers (HV) was measured using a Shimadzu HMV-2 digital microhardness testing machine. In each specimen, four measurements were performed, two in each broken piece of the specimen, distanced 15 and 30 mm from the two edges, as seen in Figure 5.