Preview

Anjitha and Tiffany here! For our final project, we cast eight white and pink/red PokePawns!

Introduction

When we were first reading over the assignment, neither of us had a clear idea of what we needed to produce to make the chess pieces. We were so glad that Dr. Wettergreen demonstrated the positives that we needed to make in order to produce the molds for our chess piece! Now comes the hard decision… what were we going to make! We didn’t want to spend too much time looking so we browsed through Thingiverse individually for 15 minutes and initially wanted to do a Bulbasaur shaped chess piece! But unfortunately, given Bulbasaur’s body, we were advised that it would be difficult to produce our CNC half. We were both heavily drawn to the Pokemon-themed chess pieces and so we decided to go with the Pokeball-shaped pawn which gave birth to the PokePawn! 

3D and CNC Positives 

Immediately after choosing our piece, we sent the shape to the 3D printer to be completely printed. This print would be used to understand how big or small we wanted our chess piece to be. After discussing with Dr. Wettergreen, he suggested that our PokePawn size be reduced to have a base width of 38.1mm. We adjusted our size accordingly and used these dimensions to produce our 3D and CNC positives. 

We were both fairly unfamiliar with using Solidworks and MeshMixer so we decided to tackle the CAD portion together. Thankfully, Rafe had recorded the process and we were able to follow along and create the base for our 3D and CNC halves. We split our PokePawn along the coronal plane which split the PokePawn into anterior and posterior ends (front and back). We planned for the front half of the PokePawn to be 3D printed to preserve the details in the button. The CNC half would then be the backside of the PokePawn. 

When creating our base structure, Dr. Wettergreen suggested that instead of creating a separate port to pour the cast into, we align the bottom of our piece to the bottom of the base to create an opening. That was definitely a pro tip and saved both of us time during the CAD portion of this project. 

Once we were done with the CAD, the 3D file half was sent to the 3D printers. We must have sent the dimensions of the original, not the scaled down version,because the first 3D part we printed was significantly larger than we intended it to be. So we made sure to scale it down so that the base width was 38.1mm and resent the front half to be 3D print. 

The CNC half still needed additional work before the file could be printed. We had to prepare the file in VCarve and create the toolpaths to cut our piece according to Douglas’ instructional videos on Canvas. We had intended to do the initial rough pass using the 1/8th inch bit on the Nomad, but that would have taken 4 hours to complete, with an additional 1 hour to complete the final pass. Instead, we took our CNC file down to the Shapeoko downstairs and tried using the 1/4th inch bit for the rough pass instead. That cut down our total time for both passes to around 20 minutes! 

Molding

We decided to cut our CNC file and mold both sides of the chess piece in the same day given the amount of time needed for the molds to harden. Our 3D printed half was ready for molding as Anjitha was able to create a box of indeterminate sides and attach it to the positive. After our CNC half was completed, we created another box of indeterminate sides as we didn’t set enough height for us to use the CNC half on its own. We followed the videos recorded by Dr. Wettergreen and calculated the amount of silicon necessary to get approximately 1 cm above our chess piece. What we messed up on was that instead of dividing the volume of our shape in half, we kept it as is because we figured that we were molding both sides of the chess piece positives. BIG MISTAKE! We ended up with more silicon than we needed and we knew we couldn’t waste it because of how expensive of a material it is. Quickly, we asked Raniyah if we could use the remaining silicon to mold her and Vanessa’s 3D positive that was ready. They agreed and lo and behold– we had just enough to fill their mold to their designated line! Phew! 

   

The next day we checked back on our molds and they were ready to be removed! It was harder to remove the hot glued pieces of cardboard than we thought but we were left with 2 halves of our PokePawn. Also the buttons we included ended up being on the same side so that was a fail… which we thought we made sure not to do but it ended up happening anyway. If we were to do this project again, we would put all the buttons on either the CNC or the 3D part and all the holes on the remaining part in order to prevent this mistake from occurring again. Additionally, we would make the holes a bit bigger so that the two molds could better fit into each part. 

Casting 

To create the support that would hold our mold securely, we used two pieces of plywood and attached them to the backs of our bases to firmly press the molds together. The flat plywood also helped distribute the tension to keep the mold from forming as gaps. We used 5 rubber bands to secure the rig and voila! The rig did a great job at ensuring none of the plastic cast would slip out between the molds and was overall very effective at keeping the halves together.

When casting, we made sure to do our math right in order to prevent any excess use. We took the volume of our 3D printed PokePawn which was 29.56 cm3 which we then converted to 0.99 oz. Because the plastic required a 1:1 ratio of Solution A to Solution B we determined that it would take 0.5 oz of each solution to create a single PokePawn. We did our casting in 2 sessions, a white session and a colored session. We converted 2 oz to 57 grams of Solution A and Solution B and we poured them into designated cups. We decided to go this route because it was difficult to pour the solutions into small measuring cups. When we did the colored session, we also used 57 grams of each solution but added a drop of red dye to Solution B. 

To mix the solutions, we poured each solution into its designated measuring cup and then combined them into a separate cup to mix and pour into our mold. After we had poured a third of the way into the mold, we paused and swished the mix around the mold before filling it up all the way to the top. After 10 minutes, the cast solidified, and we were able to pull out our final PokePawn product from the mold! We repeated this process until we got 8 PokePawns that were white and red-ish (haha!).

There was some misalignment between the halves when the final casts came out, so we attempted to sand the junctions (using 120 grit sandpaper) as much as possible to create a smoother transition between the parts. We believe that the bigger buttons that are correctly fitted could help align the molds better if we were to do this again. Additionally, the rubber bands and boards we used to keep the molds together and prevent leaking may have ended up squishing the final product. We could potentially attempt to use fewer rubber bands next time. 

Cost Analysis 

• PLA used for 3D prints from 3DprinterOS: $0.99
• 1.5” Wood Block: $12.99
• EasyFlo 60 Liquid Plastic Part A and Part B (3.8lb kit): $54.47
• Platsil 73-25 Silicone Rubber Part A and Part B (2lb kit): $52.00
• Red Polycolor (1oz): $12.50 
• 120 Grit SandPaper: $5.55
• Popsicle sticks: $4.99
• Plastic Cups: $7.99
• Labor: 13 hrs at $7.25 per hour = $ 94.25
• 3D printer: from OEDK
• CNC Machine: from OEDK
• Total: $245.73