For our midterm project, Oli and I were tasked with succesfully casting 8 copies of a chess pawn. The guidelines went further however, and stated that the pawns had to be cast with a mold made from two different positive copies of the pawn, one CNC’d and one 3d printed. While this project was intially daunting, we got to work and started discerning which direction we wanted to go with the style of the pawn. Dr. Wettergreen gave us the green light to iterate on a preexisting design, so we took this pawn off of thingiverse.com to start our design.
After downloading the file and opening it in fusion360, we decided to reduce some of the sharp angles in the original design by adding a few curves, and then we went ahead and printed a copy so that we could confirm that the feel felt right. This printed copy proved very useful later while we were adjusting our mold.
insert picture of printed copy
We liked this print, and then sliced our fusion file in half to print the half positive. We printed a few copies intially to lock down the size, and after recieving some feedback from Dr. Wettergreen and Adulfo we added a few aspects like the pegs and pour wedge which you can see in the picture below.
(our final 3d printed half positive)
Next it was time to tackle our CNC’d half positive. We were tasked with completing this aspect of the project on the Carvey CNC router. Unfortunately in order to prepare our .stl file for the printer we had to go through a lengthy file setup and conversion process. This entailed making the shape just a shell, defining the bounds of the wood we were going to cut it in, and setting the parameters for our two cuts, one rough and one smooth. Once we had done all that we were excited to begin cutting, however our first few attempts were suboptimal.
(our first choice of wood proved to be an issue for the Carvey and it resulted in these two miscuts)
We saught out advice, and decided to change our wood type. This was luckily the only issue, because our next cut came out very nicely.
(the Carvey in action and a photo of the finished CNC half)
However we did have one unpictured issue. During the second pass, we decided to use a 1/16 in router bit, however the flute length was shorter than the depth of the cut that we had made originally. This resulted in the shaft of the bit running into and snapping off both of the alignment pegs that we had cut into the piece. After some thinking, we made the choice of instead drilling holes into the wood which would result in positive pegs being cast. In order to do so we had to attach an additional piece of wood to the bottow of the piece.
(after a pretty straightforward use of the drill press we were ready for action)
Now that we had both halves, it was time to move on to molding. We were working a little bit ahead of the resst of the class and so we worked on other projects for a class day or two, but then we got to make our first mold! We choose to start with a silicone mold of the 3d printed half.
(the freshly poured mold and the crisp newly finished mold we got out of it)
In order to pour the mold for the wood half, we needed to add material to the piece bc the depth of the cut matched the depth of the half pawn. In other words, if we poured the mold as is, there would be no depth of material behind the proudest part of the piece. We used hot glue and cardboard to create a “box of indeterminate size” around the piece. We then mixed and poured the silicone, this time using a different hardness because we had run out of the other one. Once again our mold came out very nicely the first time!
(the fresh silicone mold clearly shows the pattern left by the CNC)
Having successfully created both of our molds, we went about casting our first silicon mold. This involved mixing the two liquids included in the EasyFlo liquid plastic set in a 1:1 ratio, aiming for a total estimated volume of about 30mL. Being our first attempt, we did not add a dye to our mixture. After combining and thoroughly mixing the two solutions for about 30 seconds, we poured the resulting liquid into our assembled mold, which was supported against bending through the use of cardboard and elastic bands.
(our cozy lil new pawn in his home)
The result of the first attempt was not ideal. It seemed to be the case that our molds were misaligned on the inside, despite being cut to flush on the outside. As such, it was clear where the two halves of the mold were, and the attempt had to be discarded.
(rip new pawn came out crooked)
Fortunately, we had 3D printed a copy of the pawn design earlier in the semester, so we had an easy solution to this issue. Our solution was to place the pawn inside the mold, thus ensuring that the inside would be aligned, and then remove excess material from the sides of the molds in order to ensure that the outside edges of each mold would be flush while aligned correctly, and thus able to be supported correctly by the cardboard and elastic bands.
Our attempts following this went almost perfectly, with only slight misalignments on some attempts. However, these errors were easily fixed with a razor, and these versions ended up being essentially indistinguishable from the perfect attempts.
We used several different dyes in our final set of pawns. We started off with whole colors, adding the dye prior to mixing, and thus resulting in a homogenous color. Later on, however, we experimented with mixing the EasyFlo solutions first, then adding the dye right before pouring into the mold, with only a second of light stirring. This resulting in a nice swirled pattern on the final product.
(our beautiful family of pawns)
Resulting materials
- 10 pawns (8 production quality)
Materials
- $123 per bottle EasyFlow 60 Liquid Plastic (1 gallon/ 3785ml, 10x15ml per bottle)
- 150 / 3785 * 123 = $5
- $145 per bottle 4kg, 143g
- 0.35 * 145 = $5
- Plywood sheets
- 3D printing materials: about $1/hour
- Source: https://acrl.ala.org/techconnect/post/how-to-price-3d-printing-service-fees/#:~:text=For%20an%20hour%20of%203D,hour%20of%203D%20printing%20time.
- 10 hours
- Total = $10
Total Materials: $21
Time
- Douglas $15/ hour
- Oli $15/hour
Initial Planning and design:
- 2 hours each (4 hours total)
3D printing and collection
- 2 hours each (4 hours total)
Carvey:
- 4 hours each (8 hours total)
Producing Molds:
- 2 hours each (4 hours total)
Casting:
- 30 mins per pawn (4 hours total)
Total Labour: $15/hour x 26 hours = $390
Total Cost: $411
