This month in EDES 210, we molded and casted our very own chess pieces! It was a long process that consisted of many steps, but we genuinely enjoyed seeing the final product come together. First we began by choosing our chess piece from Thingiverse. We had to keep some geometric constraints in mind, such as avoiding overhangs and having a symmetrical piece for ease of molding. We decided to choose this very cute cat pawn as our chess piece. Next, we 3D printed the cat pawn at our scale of choice (approximately 3 inches tall) to show the teaching team.
Figure 1: Initial Model
We received feedback to upscale our piece to be 4 inches tall for the rest of the project, so we updated our model the following day. However, we were soon asked to scale it back down to the original size to conserve resources. It is important to note that our pour calculations were calculated for the volume of the 4 inch piece, which led to some issues in future steps since we forgot about our rescaling. Once we finalized our chess piece choice, we used Meshmixer to create a mesh of half of the piece. This first half, the side with the eyes, was used to create the mold from 3D printing. We imported the file into solidworks to create a base for the half, adding appropriate sized pegs so the mold could close. Once the file was created, we 3D printed the model for use in class.
Figure 2: Half with base
Next, we created our first mold half in class. Using our 3D printed mold half, we built a cardboard box around it to hold in the mold material. To create the mold we used a silicone mixture, and double checked our solidworks file to get the correct volume of silicone we needed to pour into our box (sample calculations below). We mixed about 90g of solution A and 90g of solution B and filled our box with the silicone mixture, then allowed it to cure for 24 hours before removing the mold from the box.
Figure 3: Measuring Silicone
Figure 4: Creating the mold
Figure 5: Mold comparison to 3D Print
Once we had our first mold half, we moved on to creating our second mold half, which was the half of the cat that did not have the eyes. This half was created using the CNC mill. We created the file in the same way we created the first half, then uploaded it to Vcarve and programmed the file to do one rough pass on the wood block with an end mill and then do a finer pass with a ball nose to give us the look we desired. However, after we began running our code in the mill, we realized there was no ball nose long enough to reach the full depth of the piece. Therefore, the finer pass was also done with an end mill, which still came out well but with some small inconsistencies on the surface compared to the 3d printed mold.
Figure 6: First Pass on CNC
Figure 7: Second pass on CNC
We then followed the same steps to create the silicone mold from this half as we did with the 3D printed half. Some of the wood dust from the piece came off on the silicone, which unfortunately also led to us getting some dust on the pieces we made. It’s more noticeable on the first piece, and did not significantly affect the quality of our pieces.
Figure 8: Mold comparison to CNC cut
Now that we had both halves of our mold created, it was finally time to cast! Our molds seemed to align pretty well, but we also used rubber bands around the mold halves to ensure it remained sealed throughout the casting process. We were given two options for the casting material, one with a pot life of 7 minutes and a cure time of 30 minutes or one with a pot life of 30 seconds and a cure time of 3 minutes. We tried using the 30 minute cure time material for one piece, and opted for the faster curing material for the rest of the pieces. We attempted to create a gradient of blue with our pieces but ended up with one white piece, two light blue pieces, and one darker blue piece. It is also worth noting that when casting our first piece, we used too much material because the volume we had written down was for the 4 inch size piece before we scaled it down. Although we regrettably wasted resources, it was a learning experience and we were able to bring the volume down to accurate size for the rest of the casting.
Figure 9: Using the mold to cast
Figure 10: First chess piece casted
Once we were done casting our pieces, it was evident that they needed a little post processing. Since the pieces were created from two halves, each piece had a line down the middle where the halves merged. We sanded down these lines with sandpaper to make them less apparent. Additionally, we used the belt sander to remove excess material from the base and make it flat. With that, our pieces were complete!
Figure 11: Post-processed chess pieces
Materials Cost:
Silicone (90g * 2) $75/900 g -> 180g/900g*$75 = $15
Smooth cast polyurethane (amazon.com) $30/900g (40g * 4) + 40 g oops = 200/900*$30 = $6.67
Wood plank: 1-in x 4-in x 12-ft pine wood (Lowes.com) = $13 -> used 0.5 ft in length -> $13/24 = $0.54
Machine time cost:
Assuming $10/hr machine use:
3 hours of 3D printer + 5 hours of CNC mill = 8 hrs total
8 hrs * $10/hr = $80
Labor cost:
Assuming $10/hr wage:
10 hours of work * 2 people = 20 hours of work
20 hrs*$10/hr = $200
Total cost: $300.21
Overall this is pretty expensive for 4 figures, but most of this cost comes from machine use and labor cost associated with preparing the molds. Once the mold was created, creating figures was very fast!
Photo of last used workspace:
