For our ENGI 210 final project, we, Hannah Andersen and Grace Wilson, were tasked with executing the necessary steps of the molding and casting process to produce two identical chess pieces. We were assigned the king chess piece. This process included designing a positive CAD file, CNC machining the respective positive, forming a negative silicon mold, pouring a positive cast, and post-processing our final product. These steps will be described in further detail below.

We began by selecting a file representing a king chess piece off of Thingiverse. As we parsed through our options, we looked for pieces that had a symmetrical design, simple features, and no overhanging components, because the Carvey is unable to produce overhanging protrusions. We decided to follow through with the chess piece file depicted below.

Next, we pre-processed the file in Meshmixer where we sliced the piece in half. We then imported the file into Fusion 360 for further pre-processing. We correctly sized our piece, and added a rectangular base as well as pegs and holes for the cut.

We followed the proper steps of preparing our G-Code file in Fusion 360, so that it could be easily processed in Easel and ultimately by the Carvey. This included forming various Set Ups in the CAM window of Fusion 360 and finalizing many details regarding orientations, cut dimensions, materials, speeds, and bit sizes.

Next, we uploaded our file to Easel through the Inventables website and were then prepared to start a cut! We ran our first cut with two foam blocks glued together to minimize the carve time and to simply test the success of our G-Code file.

Our first cut was not a complete failure, but it did reveal a few complications. First, the depth of the cavity in which we cleared from our foam block happened to be the exact depth of one of the foam pieces. Therefore, when the carvey attempted to create our pegs, the material had nothing to secure it other than the glue, resulting in both pegs literally flying off of the base as depicted in the image below (notice, there are no pegs). We then decided that our next iteration would be CNC machined from a block of wood to avoid this problem. Additionally, in our first G-Code file, we followed our rough cut with a smoothing cut in hopes of improving the aesthetic appeal of our piece. However, the smoothing cut failed to line up with our first cut and left the positive with an even less smooth surface than before. We decided to remove the smoothing cut from our G-Code, because we were content with our piece’s appearance without it and it just created more room for error.

We then returned to Fusion 360 and prepared a new G-Code file for a block of wood sans smoothing cut. We imported the file into Easel, set up our block in the Carvey, and ran the cut!

This cut met all of our expectations; and therefore, was a success! Because we chose a symmetrical piece and perfectly centered the piece, the holes, and the pegs on our CAD file, we could just make two molds of our single wooden positive to properly form the cast.

We were then ready to make our first mold! We first filled the cavity in our wooden block with small nuts, which we then transferred to a beaker to estimate the necessary volume of molding material. We settled on using 75 grams of both parts A and B to make our mixture. As Hannah combined the liquid parts, Grace prepared the wooden block for the molding process. This included spraying the block with the mold releasing agent and hot gluing foam core supports around the cavity. These supports were necessary because the maximum protruding height of our piece was the same height as the walls of the cavity. Therefore, the added supports allowed us to pour more material to completely cover our piece and increase the thickness of the mold. We then carefully poured the combined molding material into the prepared cavity! There was a little initial leakage that we quickly fixed by further hot gluing the cracks…

We let the mold sit overnight, popped it out the next day, and trimmed the overflowing material off of the edges! We simply repeated this process to create our second mold. The two molds are depicted below.

Next, we were ready to create the casted chess piece! First, we lined up our two molded halves by connecting the pegs and holes as well as the sides of the blocks. We secured them together using multiple rubber bands.

Then, we poured equal volumes of the casting agents into two different tiny cups provided by Dr. Wettergreen. We hypothesized that these two volumes together would be enough to fill the mold. We poured Part A into a beaker, added a drop of yellow dye, and then added Part B. We quickly mixed the solution and filled the mold, having more than enough liquid to do so.

We allowed the cast to cure for thirty minutes and then disassembled the molds and removed the piece. The piece initially had a seam of excess material along the connection line of the molds. We simply sanded down the seam and the base of the chess piece, thus concluding the post-processing of our product.

Next, we repeated the casting process with a blue dye, waited for it to cure, and sanded down its base and seam. As we sanded our pieces down, we noticed that small air bubbles had formed underneath the cross of both of our pieces. These imperfections are almost unnoticeable, but we decided to attempt one last cast, because we were curious if it was even possible to avoid the formation of these bubbles. We poured small amounts of the mixture into the mold and rolled it around before adding more. We repeated this technique until the molding cavity was filled and waited another thirty minutes. After removing this piece and sanding it down, we found that we had, in fact, avoided any bubble formation in this iteration! We finished this project with three nearly identical king chess pieces that represent the superiority of Edgar Odell Lovett College.

Cost of Final King Chess Piece:

First, we must consider the amount of time we spent working on the project to finalize a labor price. After adding our time spent in and out of class working on this project, we settled on 10 full hours of labor. We have decided to charge 20$/hr as a cumulative price for both of our contributions, that we will then split between us. Moreover, the total labor cost adds up to 200$.

Next, we must consider the cost of the various materials we used. The total cost of purchasing the wood and foam for our positive CNC cuts adds up to about 7$.

The machines we utilized throughout this project as well as the various molding and casting liquid solutions belong to the OEDK but are available for us to use. Thus, we categorized these utilities under a rental relationship with the OEDK. In order to integrate these expenses into our final cost we have considered the fact that industry average for overhead, consisting of machine rentals, tools, adhesives, etc., is 15% of the finalized materials and labor pricing. This umbrella fee results in a $31.05 addition to our material and labor charges. Considering the fact that we made three pieces total, the final cost of an individual Edgar Odell Lovett King comes out to $79.35.

Closing Remarks:

We both felt that this project was a satisfying conclusion to an overall awesome semester filled with new learning experiences and creative opportunities. As we are both pursuing the Engineering Design Minor, we look forward to using the skills from this class for future engineering design endeavors. This feels like an appropriate time to say goodbye, but we will both definitely be back in the OEDK next semester so really it is more along the lines of ~see you in January~. 🙂