# Exploring the Utility of 3-D-printed Laboratory Equipment
## 3 Results
### Laboratory Scissor Jack  
The initial aim of the project was to completely replace components of a commercial metal laboraotry jack with 3-D printed counterparts, as shown in Figure 4A. However, the plastic platform was fragile due to a lack of thickness. To maintain high load capacity and reliability, a modification was needed that included (1) increasing the thickness of the top and bottom layer from 1.6 mm to 8.73 mm while all other thicknesses (such as scissors) remained the same and (2) replacing all plastic bolts and long center screw with readily available metal parts since 3-D printed threads on the plastic screw did not provide satisfactory repeatability and reliability (Figure 4B). As with the linear stage analysis, an FEA model was constructed for the three major parts of the laboratory jack: top surface, short rod, and scissor (Figure 5). For the top surface, a normal force of 100 N resulted in a maximum stress of 122.77 kPa. For the short rods, a vertical load of 100 N resulted in a maximum stress of 34,488 kPa on the middle and edge of the rods, while for the scissors, the center section of the arm was subject to a maximum stress of 16,710.9 kPa. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Type** & **Max Stroke** & **Displacement per Revolution** \\ \hline
2 in \(\times\) 2 in & \(\pm\) 10 mm & 1.27 mm \\ \hline
3 in \(\times\) 3 in & \(\pm\) 16 mm & 1.08 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Maximum stroke & displacement per revolution. Figure 4: A variety of 3-D-printed laboratory scissor jacks. (**A**) Photograph of 4 \(\times\) 4-in 3-D printed laboratory scissors jack. (**B**) Photograph of 4 \(\times\) 4-in 3-D printed laboratory scissors jack with metal screws, threaded insert, and central threaded rod. (**C**) Photograph of 2 \(\times\) 2-in 3-D printed laboratory scissors jack with metal screws, threaded insert, and central threaded rod. Since vertical translation accuracy is another important index for a laboratory jack, we compared the theoretical and experimental displacement for both PLJ and PMH-LJ under no load condition using the kinematics of the jack. The incremental height of the jack was calculated as  
\[\delta h=2\left[\sqrt{L^{2}-\left(a-t\right)^{2}-\sqrt{L^{2}-a^{2}}}\right] \tag{1}\]  
where parameter 2 originates from the double stack of the scissor platform, \(L\) is the length of the longer arm and \(a\) the length of the center rod, while \(t\) is the reciprocal of threads per inch and set to \(1/18\). Figure 6A shows a schematic diagram of the theoretical model, while Figure 6B shows the comparison among theory, PLJ, and PMH-LJ. This result clearly indicated that we can control the stroke and sensitivity of the vertical movement by simply controlling the arm length (\(L\)) and rod length (\(a\)). As expected, PLJ displayed significant deviation (up to 42%) from the theoretical model, especially at lower revolutions (equivalent to the lower height), whereas PMH-LJ displayed consistent performance from minimum to maximum height (error range of 1.4-12%). Figure 7 displays a series of load tests conducted for all three models. Figure 7A displays mass versus percentage deflection for all three types of laboratory jacks. (A) displays the % deflection for PLJ and PMH-LJ when individual height was set at maximum and 50% of maximum. Plastic laboratory jacks showed close to 30% height changes when 0.9 kg of mass was placed on top. Figure 7B shows a similar relationship for the  
Figure 5: **(A)** 100 N load applied to the 4 \(\times\) 4-in lab scissors jack platform by FEA analysis. (**B**) 100 N load applied to the 4 in \(\times\) 4 in lab scissors jack short rod by FEA analysis on both edges of the hole. (**C**) 100 N load applied to the 4 \(\times\) 4-in jack scissor by FEA analysis on the surface of end holes, extrudes and edges on front holes. (**D**) FEA result of 4 \(\times\) 4-in laboratory scissors jack platform with maximum stress of 68,471 psi. (**E**) FEA result short rod with maximum stress of \(1.25\times 10^{7}\) psi.