Final Project by Kathy and Jonathan: Cat Pawns!!

• Kathy Xu
The final for EDES 210 was for us (Kathy and Jonathan) to mold and cast a series of 4 chess pieces.

Process:

The first thing we did was to select a chess piece. At first, we wanted to choose a snoopy figurine because it was cute so we 3d printed it to get a physical idea of the size. During the first gate, we discussed with the TA’s how the project would be nearly impossible since there was overhang in many places which would be difficult to cnc or mold and cast. We then decided to switch to something easier to complete. After some long browsing on thingiverse, we discovered that it was actually a bit difficult to find a piece without overhang.
Eventually, we settled on a cat chess piece (the pawn) linked here: https://www.thingiverse.com/thing:4704681
It was a cute cat that would be easy to deal with since there was no overhang. After this, the first step of the process was to cut the piece in half so that we could mold both halves. We chose to cnc the front of the cat and 3d print the back half since we anticipated the tail might provide a bit of difficulty with the possibility of overhang.
After manipulating the thingiverse file in meshmixer, we moved to solid works, where we created the back plating for the cat pawn. This involved scaling the piece, importing the back piece from Canvas, joining them, and then also mating the faces so that it would fit together nicely. We found that some of the difficulties in this section were using the measure and mate tools, as they did not work correctly some of the time when we clicked the areas we wanted to manipulate or measure. It was a bit finicky perhaps due to our lack of experience with solidworks. We did this for both the front and back half.
The back half was quite simple to 3d print, as we just had to import and slice the file. The print came out smoothly the first time as follows:
The front half was a bit more difficult as we had to use the cnc machine and its vcarve software. Using the stl file previously created for the front half of the cat, we imported the file into the vcarve software. Here, we first dimensioned the wood piece with measurements taken from the wood calipers. We set a gap above the model according to the instructions so that the piece would be “sunken in” to the wood.Next, we created the toolpaths by selecting the appropriate bit size for roughing and for finishing. The roughing bit was 1/4″, and the finishing bit 1/8″. We calculated all three toolpaths and the total time for all three toolpaths came out toa about 1 hour. We ran into a hiccup here, as we had created the gcode file on the lab computers, and then were told that we actually needed to do it on the cnc computer. Thus, we had to redo the process. Afterwards, we had the stl. and g-code files ready for our piece to be cnc cut.

We began carving out the piece using the cnc machine. Due to the height of our wood block, the green supports weren’t able to secure the block properly, so we used the drilling machine set up to the left of the cnc machine to drill three ledges into the sides of our piece for the supports to fit in to. Each ledge was approximately 1/4″ deep.

We then secured the wood block onto the cnc machine and began the carving process. We saved all three toolpaths on the same file, which means that it would run the first 1/4″ roughing pass first and then finish with the two 1/8″ smoothing passes.

We made sure to change the drill bit when the roughing pass was finished. Carbide motion paused the process and we changed the drill bit from 1/4″ to 1/8″, including the black securing part that was attached to the bit. We then selected that we’ve successfully changed the bit and resumed the process.

Unfortunately, perhaps due to the direction of wood grain or quality of wood, the surface was not very smooth after the smoothing pass. The two pegs on the right side of block to match the holes on the other half of the mold were also gone. We consulted Dr. Wettergreen to ask if there’s anything wrong with our file or if it’s necessary for us to re-cut the wood block, but the piece got approved and is fine as long as we sand it a little. The results were pretty nice after we sanded it beginning with 250 grit and moving on to 400 grit.

After this, we moved on to the molding portion of the project. We followed the same processes for molding both halves, beginning with building the cardboard mold box around the molding part and then mixing and pouring the silicone mold. We did the calculations according to the instructions on the video and found out that we needed 180g in total, 90g of part A and 90g of part B.

We then mixed it together according to the instructions from the video and then poured it into the mold box  from a corner. The calculations turned out to be accurate and the silicone rested perfectly 1cm above the negative part.

We took the mold out and both of them turned out pretty well. During our final class, both of our parts got approved and we began pouring the final polyurethane casts. We tied both parts together using multiple rubber bands and mixed the casting liquids, which consists of 20g of part A and 20g of part B after calculation. 

After we removed the mold after 10 minutes, we realized that our first pawn was slightly deformed due to it being tightened too much from the rubber bands. We decided to not use too many rubber bands for the remainder of our pawns. The colors that we decided to use were pink, green, and blue. After taking the last blue mold out, we realized that some of the stain got stuck on the surface of the blue cat pawn, which we tried to sand off.

Here are some images of cleaned up working surfaces:

Cost Estimates:

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