# Case Study: 3D Modelling and Printing of a Plastic Respirator in Laboratory Conditions
## 2 Description of the Selected Object for the 3D Printing Process
### Modelling the Respiratory Cap  
Again, a sketch was drawn first and then the left side was created by mirroring to create a closed profile (see Figure 3). Then, the sketch was inserted into the front plane and an \"offset\" was created for it via the \"offset entities\" example. Again, this is only a 2D model. The mask cover is adjusted to four planes (plane 1 and 2, front plane, upper plane) before joining the profiles. Only then are the profiles joined using the \"Join profiles\" command. Next, the length of the planes was adjusted. The profiles were connected, and  
Figure 3: Drawing a sketch, mirroring it, and creating an “offset”. Figure 2: Finished model of a 3D plastic filter. the model was rotated so that we could see the core. Then the core is marked with the function \"shell\" (see Figure 4). To be able to breathe fully through the cover, there must be some openings in the front wall so that air can flow there. To create these holes, we needed to see the model in 2D view. Using straight lines, we laid out one hole, centered in the center. Its length was 36.7 mm and width 5 mm. Then another four were created on the left side of the model with a spacing of 4 mm. The mirroring process was applied to the right side, the alignment was checked, and the cut-out applied. For the protrusions formed on the plastic filter to have a place to fit, the handles must be cut out. These handles are created using the \"Remove by rotation\" and \"Remove by extruding\" commands. By rotation, we ensure that the semi-circular shape of the protrusion has nowhere to fit, and the extension is used to remove the material. First, one recess is formed at the top of the cover and again by mirroring it is formed at the bottom. Then we chose the view through the \"cut\" function for inspection. There are four protrusions around the perimeter of the plastic filter, which means that it is necessary to create another two recesses on the sides. Again, only one was created and mirroring was used (see Figure 5). Figure 4: Joining profiles and creating a “shell”. Figure 5: Mirroring holes and looking in planes (individual steps). The only thing left is to model the body of the respirator. Most of the steps have already been repeated, and thus drawing a sketch with planes, then joining the profiles, cutting the semi-circular holes using the rotation function. The main task was to model the body of the respirator and create protrusions with holes on it so that it can be attached with, for example, a cord and a hole to a plastic and unprinted filter. When creating a hole for a plastic filter, it started by drawing a hole in a 2D model. Its roundness and dimensions were determined. A view between the planes was chosen to check the correctness of the selection. The selection of the material was continued so that the plastic filter had nowhere to fit. Again, the first drawing in 2D models was repeated. After removal, the view into the planes and the removal of the material were selected. However, the semi-circular holes for the handles were still missing so that the plastic filter would not tend to fall out. A hole was created on the side, which was aligned exactly to the center and was created on the opposite side by mirroring. The process was repeated for the remaining two sides (see Figure 6). Subsequently, we switched to elevated body modelling. Skills in Solidworks is required to create a raised body. A downloaded model of the respirator was used, showing how it was modelled. First, a \"goblet\" was created, from which we gradually created the desired shape so that it would fit the human face. It consisted of up to seven planes if we did not count the front plane. This was followed by joining the profiles (thin walled). The model was projected back into 2D and a side view was used. When viewed from the side, it is more advantageous to model the selection of this type of material and the determination of the curve. In Figure 7 the same material selection is shown from the bottom and front of the respirator, respectively.