For this assignment, we created four chess pieces using molding and casting, CNC machining, and 3D printing. 3D printing made things easier. CNC machining made things difficult. Molding and casting could have been better. However, we still achieved a favorable outcome.
The first step was to find a chess piece .stl file suitable for CNC machining and 3D printing. We found our chess piece on Thingiverse.com. Shown below is our choice.
Happy_cat.stl
We had to remove the tail so that it would be able to be CNC machined properly.
3D printed cat
The next step was to import this .stl file into Meshmixer. In Meshmixer, we scaled the model to about 3 inches in height, adjusted the number of triangles in the mesh, and sliced the model in half. At this point we had our front half, which would be 3D printed, and our back half, which would be CNC machined.
After that, we went into SOLIDWORKS and imported the front and back halves. We then created a simple mold base out of a rectangular prism with pegs extruded out of and into the base.
We first created our 3D printed mold. We did not encounter many issues using the 3D printer.
We proceeded to create our silicone mold for the 3D printed front half. We initially used 41 mL of silicone based on our part volume of 82.7 mL. The volume was taken from Bambu Studio. At the time, we did not realize this volume was for the original STL file. We remembered that we scaled the model in Meshmixer, so this volume was incorrect. However, using the formula for the volume of silicone, we were still able to get a functioning silicone mold. This mistake in the volume would affect us later, though.
After we created the silicone mold, we began to CNC machine the back mold positive. Our piece was very ‘thick’, just barely thicker than the stock given to us. We went into the wood shop and found a piece of wood that was thick enough for the model. Since we used a ballnose endmill for the finishing pass and our wood and model were very thick, the endmill could not reach the bottom for surfacing the base of the mold positive. There were only four minutes left on the cut, too. However, the piece was still good to use for molding.
CNC mold positive
We created the silicone mold for the CNC back the same way as before, and it succeeded. It was then time to cast the chess pieces. Our very first attempt was a failure, since we accidentally took the one dye that was water-based. As we now know, polyurethane expands due to CO2 production when it comes in contact with water.
Expanded cat
For our second attempt at casting, we made yet another mistake. We did not use enough reactant. This was because the volume of our shape was not 82.7 mL. It was actually 105.7 mL. We went back into SOLIDWORKS to find out the actual volume we would need for casting. We deleted the mold base and used mass properies for each half and came up with this new, correct value.
Mixing A and B of polyurethane
Process of casting
We met up one last time to cast the four pieces. There were relatively few issues compared to last time. However, we still experienced leaking from the bottom of the mold, even with tape and rubber bands. One of us held the two mold halves together and another poured the mixture inside. We still experienced some leakage, but it was not a problem. We got it to stop leaking by putting rubber bands on the bottom and holding the rest of it together. We post-processed the pieces by sanding them.
Final chess pieces in assorted colors
Here is a photo of our clean workspace:
