Hello!
We’re Cali and Zoe, and for our final project, we decided to create chess pieces modeled after the Empire State Building (an STL file we found on Thingiverse).
This project was a culmination of several skills we developed throughout the semester, including molding and casting, CNC machining, and 3D printing.
3D Printing
We began by 3D printing the Empire State Building file and getting feedback from the instructors. Since previous teams had used this model, we kept the same size and width but decided to remove the pointed tip of the tower, as we were unsure it would print cleanly. After receiving approval from Dr. Wettergreen for the sizing and the vertical cut, we moved on to editing the model using Autodesk Meshmixer and SolidWorks.
Initially, we had chosen a different STL file, but it was too large and couldn’t be simplified enough (in terms of triangle count) to proceed. Once we finalized our halved version, we used SolidWorks to design the mold base. We created two separate files, one for 3D printing the negative mold and one for the CNC machined half.
For the 3D-printed negative mold, we constructed an infinite cardboard box and poured in our calculated amount of silicone, approximately 100 grams. We sealed all edges with hot glue before pouring. Thanks to the detail in the STL file, the fine features of the Empire State Building were well captured in the cured silicone.
CNC Machining
To create the other half of the mold, we used the CNC machine with our corresponding file. Following the online instructions, we secured a piece of wood in the Shapiro and modified the VCarve file to set the proper depth. We ran into a few issues—specifically, the 3D Roughing toolpath was estimated to take 15 hours, even after adjusting to a larger end mill size. In contrast, the 3D Finishing pass took only 35 minutes. After some trial and error, we successfully machined the negative mold, though some of the finer details from the original STL were lost in the CNC version. As with the 3D-printed half, we used approximately 100 grams of silicone to create the mold for this side of the Empire State Building chess piece.
Molding and curing
To cast our final chess pieces, we used Smooth-On 300Q, which has a 30-second pot life and a 3–4 minute cure time—making it incredibly efficient to work with once we realized we were using 300Q and not the regular 300!
To secure the mold, we aligned the two cured silicone halves and sandwiched them between two additional CNC-milled wooden pieces. We held everything together with rubber bands to ensure a tight seal. Because our chess piece was relatively small, we used about 15g each of Part A and Part B in a 1:1 weight ratio. After evenly mixing in pastel pigment with Part B using a popsicle stick, we added Part A and stirred quickly. At around the 25-second mark, we poured the mixture into the mold and let it cure for about 5 minutes before demolding.
Since the two halves didn’t always align perfectly, we used an X-Acto knife to trim away any excess material. We repeated this process three more times to produce our final set of four pastel chess pieces.
Overall this process was simple and fun, especially getting to combine multiple equipment and techniques we learned throughout the semester into one final product. We’re both so happy we got to take this class during our final semester at Rice!!
Cost Analysis
| Material | Cost |
| One 1.5” x 3.5” x 6” block of wood | $0.24 |
| PLA | $0.43 |
| Silicone Mold | $5.00 |
| Smooth On 300Q | $12.21 |
| Popsicle Sticks | $0.2 |
| Cardboard | $0.50 |
| X-acto knife | $5.97 |
| Hot glue gun & Sticks | $17.99 |
| Labor | $255 |
| Total Cost | $297.54 |
Clean Up
