Group members: Antonija, Katherine, Xinyin (Sing), Wen-Yi
- Introduction
Our mission is to create the pelvic frame for cervical models. As an overview, we used Adobe Illustrator and laser cutting to design and create the pelvic frame, and TinkerCAD and 3D-printing to design and create the cervical holder, L-bracket corner braces, and supports. Pieces are assembled and post-processed.
2. Create the frame
2.1 Measure the original frame
The original LUCIA pelvic frame is shown in Fig. 1A. We dissembled it and measured the dimensions (Fig. 1BC).
Figure 1. The original LUCIA pelvic frame (A) assembled and (B) dissembled.
(C) Dimensions.
2.2 Adobe Illustrator
We drew the pieces in Adobe Illustrator according to our measurements. The original 1-3 has corners as pentagons (Fig. 1B). For the ease of design, we changed them into squares (Fig. 2). Additionally, we changed the screw size to 5mm.
Figure 2. Design in Adobe Illustrator.
2.3 Laser cutting
We used Epilog M2, a CO2 laser cutter, to cut the pieces. We test-cut 1-inch squares under different settings. The setting that cut through the wood and caused the least frame was speed = 12 seconds, power = 100, frequency = 10, cutting four times (Fig. 3A). For a different piece of wood, the optimal setting is shown in Fig. 3B.
Figure 3. Settings.
While cutting the wood, minor flame was observed during cutting (Fig. 4).
Figure 4. Flame during cutting. (A) ideal phenomenon. (B) minor flame.
Some parts were cut through while some were not (Fig. 5A), suggesting that the wood thickness or density could be uneven. To rescue the pieces, we used an orbital sander (Fig. 5BC). Piece 1-3 broke. Therefore, we remade it.
Figure 5. (A) Wood partially cut through. (B) Sanding the front. (C) Sanding the back.
2.4 Post-processing
We glued three pieces of 4-1 and three 4-2 together using wood glue to create two thicker pieces to serve as a sturdy bottom (Fig. 6A). Due to sanding, uneven wood thickness was observed (Fig. 6B).
Figure 6. (A) Gluing. (B) Uneven thickness.
Finally, the coarse corners and edges were sanded.
3. Create smaller components
3.1 Cervical holder
The original cervical holder is shown in Fig. 7.
Figure 7. Cervical holder (front and back).
Due to the complexity of the holder and our lack of an elastic band, we loaded the STL file of a G-Clamp online with comparable functions (Fig. 8A). Then, we 3D-printed them on Bambu (Fig. 8B).
Figure 8. (A) G clamp from thingiverse.com. (B) 3D-printed cervical holder.
3.2 L-bracket corner braces
L-bracket corner braces provide support and stability. The original LUCIA pelvic frame contains corner braces made of metals. Since we do not have the metal ones in OEDK, we 3D-printed them using PLA, which has reduced strength.
We needed 8 pieces of corner braces. In our test run, we made one piece using hole diameter = 4mm. However, the holes were a little small for the 3/4 inch screws (Fig. 9). Moreover, we reasoned that it was worth making the brace wider to enhance its supporting function.
We adjusted the hole diameter = 5 mm and widened the braces (Fig. 10). In our second test run, our corner brace fit the screw (Fig. 11). We proceeded to print the remainder seven corner braces. The settings are shown in Fig. 12.
Figure 9. Test run of the first L-bracket corner brace design.
Figure 10. Final design of the L-bracket corner brace.
Figure 11. Testing the hole size of the second corner brace.
Figure 12. Bambu settings for the corner braces.
3.3 Supports
Ideally, the supports for the cervical holders can be disassembled (Fig. 1B). Since we did not find suitable designs online, we created simpler supports, and then 3D-printed them (Fig. 13).
Figure 13. Simple supports.
4. Assembly
Since the PLA corner braces are more flexible and fragile than the metal ones, pieces 4-1 and 4-2 wobbled after we applied two corner braces. Therefore, we glued them to enhance stability (Fig. 14). The slanted base makes it easier for a user sitting upright to look down and study the cervix.
Figure 14. 4-1 and 4-2 glued together to serve as the base for the LUCIA pelvic frame.
We used screws to secure the pieces together (i.e. 1-1, 1-2, 1-3, and 2-1, 2-2), and tie them to the base via the corner braces. For the parts we want the users to assemble, we use bolts with wings, which are easier to turn (Fig. 15). For the parts that we do not want users to take apart, we use bolts without wings.
Figure 15. Bolts with and without wings.
Since the supports do not have the assembly and disassembly mechanism, we glued them onto the wood board using superglue (Fig. 16). This might increase shipping volume and the risk of damages.
Figure 16. Supports glued to the boards. (There is a metal hook on the cervical holder from a previous design to hang the holder. However, it is less stable than supports and is abandoned.)
5. Discussion
The project is deceptively simple, as the screw holes, bolts, supports, slant, and other features all require engineering considerations. Functionality, long-term stability, easiness of shipping, and cost are all factors to be considered. The total cost is around $288.5. The labor cost is around 60% of the total cost. The material cost is around $7. Please refer to the cost table for more details.
In mass production, to enhance stability and save time, I will purchase a lot of L-bracket corner braces instead of 3D printing. To save time and material, and reduce waste, I can design back-to-back cutting (Fig. 17), so that one cut generates two sides. CNC could be an easy and cheap alternative to cut and carve thick wood, reducing the number of components and the cost of assembly. As production increases, purchasing machines will be most cost-efficient than renting.
Figure 17. Back-to-back cutting. The red line is the tour of cutting, and the black line is the path left behind.
Cost table for the LUCIA Pelvic Frame
