We started our final project by choosing a really cool king piece design, with a swirling pattern. We 3D printer our piece, and received feedback to shorten our piece to 3 inches tall for this project. Next we would prepare our half-piece to be cnc machines and 3d printed for a silicone mold. However, when we went to split the king piece in the middle, we realized the piece had too much overhang due to the unsymmetrical spiraling. Overhang of this type would be impossible to create on a CNC machine, so we decided to reset and look for another design. We wanted to keep it simple and chic, so we landed on this classic pawn piece. The .stl file for our design can be found on Thingiverse, specifically under the name “Chess Set” by Intentional3D.
We scaled up the pawn piece to a height of 3 inches, since we wanted our piece to stand out more than a usually smaller pawn would. We then 3D printed this scaled up piece. Our print came out perfectly, so we were ready to start the mold making process. We used Meshmixer to cut our piece in half.
We then downloaded the 3”x4” solidworks base provided on Canvas. We combined half of our pawn with the base through mating on solidworks. We now had our 3D positive ready to be printed. We put our piece to print, and once it was ready we could move onto our first silicone mold half.
We did the 3D print half silicone mold in class. We first made a box around 3D print using cardboard, hot glue, and duct tape. We made sure to be extra careful to not leave any gaps or holes. We checked our piece by putting it up to the light and making sure all the parts with light shining through were reinforced with hot glue and duct tape.
We then prepared 230 ml of silicone mixture based on our volume calculations, which can be found at the end of our blog. We measured 1:1 ratio of each part, mixed for the instructed time, making sure to scrape the sides and bottom. After mixing, we slowly poured the mixture into a corner of our mold, to ensure a clean and even pour.
We let our piece rest for 24 hours, and once we demolded the silicone, it came out perfect!
Onto the CNC machined half of our mold. We used the same half with a base we made on solidworks. We used VCarve to place and direct the cuts, creating the gcode for the shapeoko pro. We wanted to use the shapeoko so we could use a ¼” end mill for the roughing cut to reduce the running time from 6 hrs to 3.5 hrs. We used the instructions on the tutorial to correctly adjust our settings and create the roughing and finishing cuts.
We ran into many problems when trying to create our cnc piece. On our first attempt, the cut stopped with 20 minutes left to go because someone had booked the machine after us (and never showed up). On our next try, we did not add enough supports to hold the wood because when the machine was finishing the outside edges of the cut, the piece began to shift (this also happened in the last 20 minutes of the cut). Next, we ran into some weird errors where it seemed like the gcode had become messed up and was cutting a strange strip through the middle of our pawn. After consulting with Dr. Wettergreen, we ended up using our first attempt to create the second half of our silicone mold.
We used cardboard, hotglue, and rubber bands to make a border around our cnc machined piece. We went through the same process of mixing the silicone parts, pouring, and resting for 24 hours.
Once both halves of our pawn mold were ready, we moved onto polyurethane casting. We needed 35 ml of polyurethane for our pawn, based on our calculations found at the end. We used a 1:1 ratio of part A and part B, mixing the parts quickly to avoid the cast hardening outside the mold. After mixing, we added a drop of pigment and didn’t mix it fully, to create a marbling look. We then poured the mixture into our mold, which we had secured using rubber bands. Within a few seconds, the polyurethane cast set, and we were able to demold a beautiful pawn piece. We repeated this process 3 more times, with different colors.
Once all of our pieces were done, we went back to smooth out the border between the two mold parts using an x-acto knife. While our pawns aren’t the most perfectly smooth pieces, they still came out so pretty and pieces that we are extremely proud of!
Cleaned-Up Areas:
Cost Analysis:
Time: $145
Around 10 hours for 2 people→ $7.25/ hour
Materials: $30
460 ml of silicone → $20
140 ml of polyurethane → $6
Polyurethane pigment → $1
Small wood plank → $2
3D printed half → $1
Machines: $2,500
3D printer → $500
Shapeoko → $2,000
Total: $2,675
($175 without machine costs)
Calculations:
*want silicone 1 centimeter above the top of piece
The volume of of the box:
4”x3”x1.25”= 15” cubed
15” cubed = 245.8 ml
Volume of the entire pawn: 35 ml
Silicone volume:
245.8 ml – 35/2 ml = 228.3 ml
Use around 230 ml
115 ml of each part for silicone
Polyurethane:
35/2 ml = 17.5 ml
Use around 18 ml each part
