Hi everyone!

For our final assignment, we were tasked with molding and casting a chess piece. To create the mold, we needed to make one half using a 3D printed positive mold and the other half with wooden CNC machined positive mold. Then, with these 2 halves, we poured silicone over the positives to create negative molds. These negative molds were then brought together to cast our chess pieces out of polyurethane. 

Creating the 3D Printed and CNC Milled Positives

Ege previously 3D modeled a minimalistic chess piece, so we decided to use that for our final project! With this file, we scaled it in Solidworks using the dimensions specified by the assignment. We also added cylindrical pins so that when the two silicone molds were formed, they could be held together by friction fit cylinders.  

The 3D printed positive was created using the Bambu printer. It came out very smooth and accurate to what we wanted. The wooden CNC milled positive was made using the Shapeoko and Carbide 3D Nomad 3. To use these machines, we needed to input a gcode different than a 3D printer. With VCarve, we created the gcode for the CNC. The first part of the code was a rough cut with a ⅛’’ drill bit, and the second half of the code was a smoothing cut with a ⅛’’ ball drill bit. A majority of the wood was removed with the rough cut, so the Shapeoko was first used. The smoothing cut was performed with the Carbide 3D Nomad 3. Since the Nomad is not as strong as the Shapeoko, parts of the chess piece surface are rough. We would have only used the Shapeoko if we were to redo this project.  

Molding the Silicone

To set up for silicone molding, we set up a cardboard box around each positive. This was added to prevent silicone from leaking out. Using the calculations from class, we determined that around 200 g of silicone was needed for our piece. The 200 g was split in half for part A and part B, so 100 g of part A and 100 g of part B was used to mold our silicone. After waiting ~24 hours, our molds came out very well!

Casting the Pieces

With both of our molds ready, it was time to cast! First, we held the molds together with a rubber band, and we clamped wood on the sides to ensure there were no leaks from the molds. We then used 300 polyurethane to cast our pieces. 20 mL of part A was added to a cup, different dyes were mixed in, and then 20 mL of part B was added to start the reaction. We had to complete this step fast because the life of the mixture is very short. Because of the short lifetime, the piece also set very quickly, around ~3-5 minutes! With this short step, we had 5 chess pieces in about 30 minutes! 

Reflection

Overall, this process was very fun and easy to complete, but there were some limitations with our processes. The CNC positive had some defects from the Nomad 3 machine, and this was reflected in the silicone mold. As a result, these defects appeared on our final chess piece. Using 2 positives produced by the same technique would be better instead to produce a more consistent and symmetrical piece. Another limitation was the seam generated from the casting process. Putting 2 mold halves together creates a gap where they meet. This gap can be sealed with clamps, but not perfectly. Because of this, some polyurethane seeped into this crevice, leaving a seam. We chipped at it with a wire cutter, but unfortunately, the seam is still visible. Regardless of our limitations, we are still very proud of our colorful chess pieces and enjoyed all the assignments in this class!

Cost Estimate

3D Printer Salary ($23/hr) for 1 hour – assuming labor accounts for material cost	$23
CNC Miller Salary ($25/hr) for 2 hours – assuming labor accounts for material cost too	$50
Silicone Molding Kit	$35.87
300 Polyurethane Molding Kit	$28.57
Urethane Color Kit	$38.97
Total Cost	$176.41

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