For the midterm project, Dorothy, Chris, and I created 2 rooks for playing chess. The rooks had to be cast with a CNCd positive half and a 3D printed positive half. After we created the 3D printed and CNCd halves, we had to pour silicon into each half to create the negative mold that we pour plastic into to create the chess pieces. We used this owl on thingiverse as a rook and started creating our molds.

We downloaded the file off of thingiverse and put it into MeshMixer to be sliced. It was kind of tricky figuring out exactly where to slice it given that it is not a symmetrical shape. We ended up removing the “ears” of the owl because those would have been problematic for the Carvey. We sliced the owl in a diagonal across the back; the back, which is the simpler half, would be our CNCd part and the front, which is more detailed, would be 3D printed.

 Pictured left is our sliced MeshMixer file.

After slicing our owl, we had to figure out how to lay it flat on a plane and place in on a block. This also proved to be a tricky task; Dr. Wettergreen thankfully helped us with the back half of the owl after we spent almost an hour trying the lay it flat. The front half was easier and only required minimal adjusting and rotating on Fusion360.

After the owl was nicely placed on the block, we added pegs to the corners of the block. After adding the pegs and making sure they lined up for both halves, we were ready to use The Carvey and 3D printer!

We created the CNCd half of the owl first; we had a little bit of trouble with the wood size considering the block we place the owl on was too wide in the x direction for a traditional 2×4. After multiple unsuccessful trips to the wood shop trying to search for the right sized wood, I sought the help of Douglas who found the correct sized wood for us.

After going through the file setup and importing the g-code onto easel, we were finally able to cut the back half of our owl. The first attempt was going very well; after the rough cut, we were pleased to see how nice the back half looked on the Carvey. But, when we went to do the smooth cut, things started going downhill. The pegs and our owl got obliterated by the Carvey. The Carvey also cut a hole in the top half of our owl. I realized this was because I selected the “add perpendicular passes” for the smooth cut on Fusion360, so I recut the owl and only did parallel passes and it came out quite nice. Per Douglas’s recommendation, I also reduced the bounding box for the smooth cut to be only around the owl so our pegs didn’t get messed up by the Carvey again.

 

After cutting the back half, we imported our front half into 3dprinterOS. The front half printed successfully, and we could finally move on to pouring our mold.

To created the mold from the two halves, we had to create a box of indeterminate size to hold the silicon. We also had to add a piece of Play-Doh to the bottom of our 3D printed half so there would be a hole in which we could pour the plastic when it came time to put the two halves together and created the chess piece. We used 3.5 oz of each part of the silicon mold, so 7 oz for each half. We got this value by measuring the volume of each box to make sure we didn’t waste any of the silicon.

After pouring the mold, we realized we did the pegs wrongs and extruded pegs that were supposed to be cut in. We decided to redo the 3D print and repour the mold for the front half.

After fixing the peg issue and repairing the mold, our final silicon mold of the two halves were complete! We were finally ready to mix the two parts of the liquid plastic in a 1:1 ratio and pour it into our mold to create the rook. We used cardboard and rubber bands on the outside of our mold to hold everything in place while the plastic set.

Our first rook came out pretty good, but it was a little off. We tried marking where the two halves lined up vertically with a sharpie at the top of the mold, and then lined up the two lines so the front and back would be lined up. This proved to be tricky because our pegs were off, so we would line the mold up and tie the rubber bands, but the pegs would keep shifting the mold so it was never exactly lined up. After about 10 unsuccessful attempts, we decided to cut off the pegs because they were causing more trouble than they were helping. We realized our piece took less than 30 minutes to set, around 7-10 minutes, so this discovery was very helpful in saving us time. After cutting off the pegs, we only poured 4 more times to get the owl exactly how we wanted it to be lined up! We did notice there was space at the top, but this is because when we were initially editing the thingiverse file, we cut off the ears and must’ve taken some extra material with them. We poured a whopping 14 times until we were finally able to get two successful rooks!

After de-molding, there was still a chunk of plastic at the bottom of the owl from where we had to pour the plastic. To remove this chunk, we used the belt sander and made the bottom flat so the owl could stand. We did notice there were small air pockets at the very bottom, but they do not prevent the owl from standing straight and balancing by itself. We finally ended up with two successful rooks!

For materials, we used 420 mL of EasyFlow Liquid Plastic, which costs $123 per gallon (3785 mL).  420 mL/3785 = 0.11 mL, and 0.11 mL * $123 = $13.65. The silicon is $328.90 per gallon, and we used 621 mL. 621 mL / 3785 mL = 0.164 mL.  0.164 mL * $328.90 totals to $53.96. We used two pieces of wood which cost about $2. Our 3D printed half took 9 hours and 43 minutes total and cost $1.93. Factoring in the machine cost of $1.43/hr, that totals to $1.43 * 9.72 hrs = $13.90. Our CNCd half took 4.2 hours, and at $20/hr, that comes out to $84. The total cost of materials/machines came out to be $169.44.

For labor, we spent 4 hours on initial planning and slicing, 6 hours setting up the files on Fusion360, 5.2 hours setting up the file to be sent to easel and making sure the Carvey cut the piece correctly, 2 hours producing the molds, and 5 hours casting the rooks. We also asked for help from a lab assistant for about 10 minutes and the TAs for about 1 hour. After adding everything up, the total comes out to  23.4 * $10 = $234.

Our grand total came out to $403.44.