These are the steps that Dante and I took to complete the ENGI 210 Final Project: Casting a Chess Piece.

Step 1: Selecting a Chess Piece design

The first step of this project was to select a chess piece design to mold and cast. We decided on the knight piece from the Moai Chess Set found on Thingiverse. Next, we printed the knight chess piece on the 3D printer to confirm the size of the design and ultimately decided to scale the design by 200%.

 

Step 2: Creating a Chess Piece Positive using 3D printing

To create the silicone molds to cast the knight chess piece, we designed a one-half positive of the chess piece design to 3D print. 

We began by importing the STL file of the chess piece into Meshmixer and slicing the design in half. The mesh was reduced to around 9,000 and the file was exported as a binary .STL file. 

Next, the file was imported to Solidworks to create additional geometry to the half-piece to make it easier to mold. A rectangular base along the sliced edge, two 5mm holes and two 4.8mm extrusions to align the molds, a trapezoidal pour hole, and an air tunnel was added to the design. Finally, the design was exported as an STL. file and 3D printed. 

 

Step 3: Creating a Chess Piece Positive using CNC Machining

The second half of the silicone mold was created using a one-half positive of the chess piece design that was CNC machined. 

To do this, we began using SolidWorks to mirror the STL file used for 3D print. The only changes we made to the design was to switch the location of the holes and extrusions. By doing so, the two halves of our mold will be able to be aligned. 

Next, the file was imported into V Carve Pro to modify for the Nomad 3. We followed given instructions to convert our file into g-codes for a roughing path using the ¼” bit and a finishing pass with the ⅛” bit. Finally, the g-codes were sent to the Nomad 3 to carve out our chess piece positive out of a 2″x4″ wooden block. 

Step 4: Creating Silicone Molds

The chess piece positives created through 3D printing and CNC machining were used to 

create silicone molds out of a two part mixture of Plasil silicone rubber. We used cardboard to extend the walls around the 3D-printed and CNC-machined chess piece positives so our molds would have some thickness to them. To create the silicone mixture, instructions on the containers were followed carefully and we had little to no problems with this step. After leaving the molds to cure overnight, they were ready to use for casting. The pine sap from the CNC-machined chess piece positive caused half of the molds to be slightly sticky, which was not a major problem when casting. 

Step 5: Casting the Chess Pieces

The final step was casting the chess pieces using the negative molds. To do this, we assembled the two halves of the silicone molds using the alignment holes and extrusions, and held the molds in place with rubber bands. We created a mixture of EasyFlo 60 liquid plastic following the instructions on the container and poured it into our mold. Each chess piece took around 15 minutes to cure. 

In our first round of casting, we underestimated the volume of liquid plastic we needed so the chess piece came out slightly shorter than expected. For the next cast, we made sure to make enough liquid plastic mixture without being wasteful. For the last 6 casts, we added color dye to the mixture so our chess pieces came out in colors of red, blue, yellow, green, gray, and black. 

Because one half of our mold was sticky from the pine sap, the mold slowly degraded as we casted more pieces. Thus, a decrease in quality can be seen as more chess pieces were casted. 

 

Cost Analysis

• 2” x 4” wooden piece = $2.98
• 3D printing material = $0.60
• Platsil 73-25 Silicone rubber = $63.00
• EasyFlo 60 Liquid plastic = $65.72
• Casting dye = $12.00
• Monthly membership for access to tools and machinery (3D printers, CNC machine, etc.) = $50.00
• Labor: 2 people x 5 hours x $15/hour = $150.00

Total: $344.30