In this final project, Annanya an I  aimed to mold and cast chess pieces with 3D printed and CNC machine to mold two halves of chess pieces.

We selected a chess piece 3D STL file in thingiverse and import into MeshMixer software. We asked advice from TA and Dr. Wettergreen, and we were suggested to change a chesspiece with solid bottom instead of hollow part. And we chose the Pokémon ball as our chess piece model. We lower the mesh number down to 1000 for further processing and cut it half for positive molding. The half model was imported into solidworks to modify the shape of chess piece with a base and four dowl pin structure. we rescale the chess piece to 4.3 in * 3.2 in to meet the requirement. Since our part is not axisymmetric, we needed a mirror geometry to use for our CNC side positive geometry.

Using the 3D-printed structure as a foundation, we attached cardboard walls using hot glue to create an enclosure. Additionally, we sealed all the edges with duct tape to prevent any silicone from seeping out. Next, we combined parts A and B of the silicone and mixed them for a total of 10min before pouring the mixture into our 3D-printed Pokémon ball model. During the pouring process, we noticed an abundance of air bubbles within the silicone, raising concerns about potential gaps in our final ball mold. To address this issue, we adjusted our pouring speed and gently tapped the 3D-printed piece against the table to eliminate some of these bubbles. After allowing the mold to set for a day, we carefully removed the silicone mold from the 3D-printed base and were delighted to find it turned out impeccably. The initial worry about air bubbles causing gaps proved unfounded. We were now ready to proceed with our CNC work.

The opposite side model as the other half positive mold was used for generate thee file for CNC machine with the help of VCarve in the OEDK computer. We used a 1/4” rill bit for 3D rough cut and 1/8” drill bit for finer finish cut to make this positive mold smooth enough. As the width of wood block of 3.4 in is just little bigger than the width of chess piece of 3.2 in, the wall on the left and right side will bit cut out by 1/8′ drill bit. For the next part of silicon molding, we added cardboard on both sides to stop the liquid leaking. This CNC machine is the most difficult part because the wood block always slightly move under the rough cut, and have to pause it to tighten the screws and retape the wood bottom.

Next, we combined the silicone components and poured them into the CNC component. Afterward, we gently tapped the mold to ensure any potential air bubbles were expelled.

We assembled the two halves of the silicone mold and secured them using rubber bands. Subsequently, we poured an equal volume of Part A and Part B of the plastic material and swiftly blended them before pouring the mixture into the mold. It was quite intriguing to observe the material heating up as a result of the exothermic reaction and undergoing a transformation into a white color as it began to solidify. We patiently waited for the complete curing process to take place and then proceeded to remove the mold.

We repeated the step of pouring liquid plastic for eight times and make eight pieces of chess. The only thing we could improve is to make the alignment more precise because there was slight misalignment when we put two negative molds together. honestly, the main reason is we consider our shape is asymmetrical, and we flip shape of Pokémon ball and even four fixture pins, which accidently make the two negative model have the exactly same pins instead of opposite pin to fit each other. We manually modify the silicone molds and make them fit. The multiple colors look fantastic with Pokémon ball shape. Also, we are able to see the texture of each half is quite different with 3D printed and CNC machine, and i prefer 3D printed one for molding due to smoothness.

Cost Analysis:

Material	Cost	Source	Quantity	Total
wood block FDM Filament	$12.49 for 4 $13.99/spool	Amazon Amazon	2 0.3 spool	$6.25 $4.2
Silicone	$79.99/gallon	Amazon	0.15 gallon	$12
Plastic	$145/gallon	Amazon	0.2 gallon	$29
Prototyping Engineer (including machine use)	$38/hour	ziprecuiter	5 hours	$175
CNC Operator	$24/hour	ziprecruiter	1 hour	$24
Overhead	14 cents/kWh	Energysage	0.5 kWh	0.07
Design	Free	Thingiverse		$0
Total				$250.52

(cardboard is not considered)

Total cost: $250.52