Product

Eight plastic pawns

Procedure

I started by finding a file for a pawn on Thingiverse. I picked one that’s rather basic, but it’s symmetrical, which would make a lot of things easier later in the production process. Once I had its STL file, I opened it in Meshmixer to cut the pawn in half. Then off to Solidworks to add in the base and create a positive mold.

I then 3D printed two of these molds (if I had done an asymmetrical model, I would have had to make two different molds). Unfortunately, I forgot to add the walls and pegs. Some cardboard and an extensive amount of hot glue were used as temporary walls when I poured in the two ingredients that would form the silicone negative mold.

Once the molds were done, I took out the walls. I had two molds, but they lacked pegs. To fix this, I found a dowel and cut four small pieces to fit in the holes, then superglued them in.

My first attempt to pour the liquid plastic didn’t go so well. The mold wasn’t held tightly together, so a lot of the mixture leaked out. That’s how I got this strange looking little guy.

After a while, I figured out that the reason the mold fit so loosely despite using rubber bands was that the dowel pieces I cut were too long. The mold was actually being held open by them, not closed. I sanded the pegs down, then retried. This time it fit a lot better when I put rubber bands around the mold, and there wasn’t much leaking as I made the next 7 molds either.

One feature that is interesting is how the two pieces are a tiny bit misaligned from each other. I think it’s just from the molds not lining up exactly when I rubber band them, so it’s technically a defect, but I kind of think they look cool when all of them have the same offset.

Challenges

Creating the file for 3D printing was a bit frustrating because there were a lot of steps that had to be exactly right, and Solidworks can just be frustrating in general, but I was able to get a functional file (well, minus the walls and pegs). The most challenging part, which did impact the final parts’ quality, was stopping the leaking and getting the mold to line up correctly. Some of this was due to the impromptu dowel pegs, while some of it was imperfections in the shape of the mold itself.

If I were doing this project again, I would definitely remember to put in the pegs on the sides of each 3d printed files. That would have helped the issue with leaking and also the general fit of the mold. Also, I would have done more post-processing, especially to the bottoms. Some of them still have edges on the bottoms, but I simply ran out of time to finish them due to finals season.

Cost Analysis

Materials used: $1.05 of 3D printing filament (from 3DprinterOS website)

Cardboard and dowels for making walls and pegs: negligible (used scraps found around the OEDK)

Silicon mold (Platsit 73-25): 2 * 0.5lbs * 180 (for 8lb bottle kit) = $22.50

Liquid plastic: 8 pieces * 0.1lbs * $100 (for 7.2lb bottle kit) = $11.11

Labor: 2 hours preparing file and 3D printing + 4 hours making casts (30 mins. Each) = 6 hours @$20/hr = $120

Total cost: $154.66