For our ENGI 210 final project, we were tasked with creating chess pieces through a combination of CNC machining, 3D printing, casting, and molding. We had the option to either create two complex pieces or a set of eight identical pawns. We decided to create two complex pieces, specifically we chose a queen piece from a cow chess set made by flyingpurplecow on Thingiverse. 

Our first step was to print out the original file to get a feel for the size of the features. Based on this first print, we then printed a second version at our desired final scale.

Our next step was to prepare the file so that we could CNC machine a one-half positive of the piece and 3D print the other positive half. We worked on Fusion 360 and used a tutorial provided for us to set up the file for CNC machining. We scaled the file and split it along the frontal plane, right in front of the crown and ears.

Our first challenge arose during the scaling because we realized that Fusion360 was automatically scaling up the piece by a factor of 10. We resolved this issue by selecting “do not capture design history” immediately after importing the file into the program. We also added base to each half, as well as pegs/holes on each base to improve the mold alignment later on. 

Our next step was to print the back half (with the ears and crown) and CNC machine the front half. The printing was quite straightforward and was successful on the first try. The CNC machining was also successful on the first attempt, but we had difficulty finding a piece of wood that was thick enough for the model while being thin enough for the Carvey. We resolved this by editing the file to make the base for the chess piece thinner.

On Fusion 360, we made a rectangular base for the face to sit on, a pour hole, and two holes for the 3D printed pegs to fit into to help with alignment. During simulation, we created two different simulations: one rough cut with a 1/8″ straight bit, and one smooth cut with a 1/16” upcut bit.

After creating the files, we uploaded it to Easel and began to mill the piece. The rough cut turned out really well; though it wasn’t as detailed as I expected (some sharp edges were a bit round due to the size of the bit). Running the smooth cut, however, resulted in a rougher cut than the rough cut. We believe this was due to the bit we selected: there were distinct lines where the passes occurred, but we were able to sand down the surface to smooth out most of the lines.

With the finished positive halves, we made two half negative molds. To do so, we attached cardboard walls to the two positive molds and poured two-part liquid silicone over them. We left the silicone to cure for a few hours. 

Once the silicone mold was set, we were ready to cast the pieces. We started by aligning the two halves, using the pegs as a reference, and joining them with rubber bands. Then, we made mixed the liquid plastic by combining EasyFlo part A and part B in a 1:1 ratio by volume. We poured the liquid through the mold and let it sit for a few minutes before removing the formed piece from the mold.

As soon as we removed the piece, we immediately noticed we had alignment issues because the front and the back of the piece were slightly off. The piece also had some air bubbles at the base and the cow’s ears were partially complete.

We repeated the casting process and attempted to address these concerns. To eliminate the  air bubbles, we experimented with moving the mold around and tapping it as we poured the liquid plastic. Doing so did help remove the air bubbles, but unfortunately it didn’t help fill in the ears, likely because the ear holes in the model were too small. We decided to simply break of the ears and sand down any remaining material. To improve the alignment of the piece, we played around with the placement of the two molds. None of the attempts completely fixed the problem, but we were able to cast some pieces with minimal alignment problems.

Once we got the hang of the process and were somewhat happy with the outcome, we decided to cast our final pieces. They differed from the previous pieces in that we colored them in blue and pink (one for each opposing team). To color the pieces, we mixed blue or pink dye into either the EasyFlo Part A or Part B before the two parts were mixed together and poured into the silicone mold. It was a success!

The final step in the creation of the queens was to post-process the pieces. We started by sawing off the excess material formed from the pour hole and using the belt sander and sandpaper to even out the base. We also used sandpaper to even the misalignment. 

And with that, we were done. Ta-daaa!

Cost analysis

Labor

• Approximately 8 hours of labor, $15/hour = $120

Material

• PLA filament (calculated by 3DPrinterOS)= $0.41
• Wood sold for $9.99 at Rockler. We used approximately ½ of that amount, so $9.99/2=$4.99
• EasyFlo (1 pint) sold for $24.00 on Brick in the Yard Mold Supply. We used approximately ⅓ of that amount, so $24.00/3= $8.00
• Liquid silicone (1 pint) sold for $45.00 on Brick in the Yard Mold Supply. We used approximately ½ of that amount, so $45.00/2= $22.50
• Sand paper (6 sheet pack) sold for $4.27 at the Home Depot. We used approximately 1 sheet, so $4.27/6= $0.71
• Dye (2-3 oz bottle) sold for $6.72 on Amazon. We used approximately ⅕ of a bottle, so $6.72/5= $1.34
• Plastic cups (200 pack) sold for $19.99 on Amazon. We used approximately 10 cups, so ($19.99/200)*10= $0.99

Equipment

• Membership at a makerspace (TXRX) to use the same equipment (3D printer, CNC machine)= $50

Total

$120.00 +$0.41 + $4.99 + $8.00 + $22.50 + $0.71 + $1.34 + $0.99 + $50 = $208.94