Outcome

The first step was to add very soft clay to the existing mold to the halfway point. When the silicone is poured in, I needed to make sure that it would not leak anywhere that it was not supposed to. I had to push the clay very close to the mold and make sure it got all the way to the foam core walls. I also used lots of hot glue to close up the seams to prevent leaking. 

I then mixed the silicone with the hardener. I did some volume calculations to see how much of the material was necessary to fill the box that I made. We then put the well mixed silicone and hardener into a vacuum to get rid of the air bubbles in the mixture. Finally, I poured the first half of the mold very slowly into one corner and let the fluid fill every crevice. 

There were no leaks! The silicone settled nicely for the first half. 

This is the bottom of the mold when it finally hardened and I took the foam core off. I peeled away the white clay and revealed the other half of the model. 

I took this scraping tool to clean up the left over clay and any other inconsistencies. 

I then put new foam core walls up, applied lots of hot glue, and poured the second half of the mold. 

Here are the two halves with the model taken out. There were definitely some errors that I would fix if I could start over, but overall, things looked okay. 

Here you can see the mold rubber banded together to apply some pressure to keep the two pieces together. I had to add two funnels because I have two cavities for the plastic to flow into. 

This is my first part. The chambers were full, so these parts were just left out to harden on the shelf. There were some minor bubbles, but overall the first iteration was okay. 

This is my second part. I was able to put this one in the chamber. I had a similar issue when pulling it out of the mold. I cracked off part at the top. I also made a mistake with the placement of the funnels. I shoved them too far into my mold and it actually made holes in the plastic part. I made sure to make not of this and fix it for the next time around. 

This is my final part. As you can see, the orange one is pretty rough right out of the mold (the green is already sanded in this photo). However, I was able to take a file and make the surface pretty smooth. I was able to completely eliminate the leftover material from where the funnel was. 

I was also able to remove and sand the parts without breaking any pieces off. The hardest part to sand and the place that looked the worst was the parting line. If I were to cast once more, I would add a bunch more rubber bands to try and really pull the two sides together. I had a lot of leakage, especially on the last one because I was being conservative with the amount of rubber bands that I used. 

Here are a couple of nice photos of the final product. I honestly think a lot of the imperfections came from my work with the white clay. When I was packing that in, I think I added a lot of non-smooth surfaces and created some bumps that were not there previously. Overall, I think the pouring of the plastic went well. I didn't really have any bubbles and the liquid got into almost all of the crevices.