Modeling

For our final project, we (Renee and Janie) chose to make cat chess pieces. When modeling our CNC-ed half, we ran into overhang issues due to the cat’s crown, ears, and tail. Thus, we had to cut the cat at an angle to have all intricate parts (crown, ears, tail) be 3d-printed while maintaining the requirement that the CNC-ed part is about half of the model. 

 

Creating the Molds

We first 3d printed the half with intricate details and then created a negative silicone mold using it, with the help of cardboard, hot glue, and duct tape.

Then, we CNCed the remaining half and created a negative silicone mold using it, using a similar process as shown for the 3d print mold above. Unfortunately, our piece of wood moved slightly during the beginning of the cut, so there was a slight gap from the wood being cut too far, but we were able to fill this with a little bit of joint compound before pouring the silicone, and it fixed it pretty well. Also, when going to assemble our mold halves, we realized that the pegs were wrong on our model and didn’t match on each side, so we added some small dowels in the correct place to help with alignment.

 

Casting!

We casted eight chess pieces by joining the silicone molds using rubber bands and small c-clamps. Our first two attempts had major bubbles in the tail, where the plastic was not reaching the very end. We solved this issue by repurposing a straightened paper clip to push the plastic down the tail and break the surface tension that held the bubble. We also used the paper clip to ensure the ears and the crown did not encounter similar, bubbly issues.

We removed casting artifacts first by sanding, but later realized that cutting off the small amount of excess plastic with the ultrasonic cutter was cleaner and more effective. Finally, we painted the crown and the collars gold, as a finishing touch.

Reflecting on this process, we realized we made a mistake while modeling the two halves, where the alignment pegs and holes did not match up. We had to improvise by carving out new holes in one of the silicone molds and then constructing pegs using a sharpened wooden dowel. This worked, but having pegs/holes that align and also go deeper may have made the casting process smoother.

We also could have modified the cat model to have a larger collar. It was a little too small, so the CNC machine was not able to accurately cut the shape out.

 

Cost Analysis:

• 3d Print: $0.46 (estimate from 3DPrinterOS)
• Wood: ~$13 (Home Depot)
• Silicone: $20 (Amazon)
• Casting Plastic: $30 (Amazon)
• Paint: Negligible
• Labor (2 people x $10/hr x 14 hr): $280

Total: $343.46 (expensive chess pieces!)