Ana and I finished our BIOE555 journey with this final project! For our project, we decided to mold and cast 8 king chess pieces that had a modern look. We 3D printed and CNC milled each positive mold half of our piece, used silicone to create negative molds, then used EasyFlo 60 to cast our chess pieces.

3D printing and CNC Milling Positive Molds

To start with this project, we found our desired king chess piece. We followed the instructions to cut our piece in half and used SolidWorks to line it up on a mold base. We made sure to split our chess piece in half so that one half (the CNC milled half) would not have any overhangs. On the 3D printed piece, we included a “breathing tube” to avoid big air bubbles in our final cast pieces.

For the CNC half, we set up the g-code file to include a roughing pass with a ⅛” mill bit, then used a down cut ¼” bit for a more detailed pass. We increased the feed rate to 200% of its original speed to ensure that the cut finished in the time we had to complete the cut.

 

Creating Silicone Negative Molds

To create the silicone negative molds, we mixed the silicone rubber Part A and Part B in a 1:1 ratio by weight, which required 250 g total for each mold. Given the cost of the material, it was important to be exact with our measurement of the necessary solution. We started by measuring the volume of the “box” of the mold and then subtracted the volume of the half chess piece of 18.23 cubic centimeters. After some quick conversions, we determined that we’d need 125 g of Part A and 125 g of Part B for each mold. There were some bubbles formed, but most of them disappeared on their own. We created the cardboard encasing to contain the solution and added duct tape and hot glue to prevent leaks. Unfortunately, we later found that adding hot glue to one of our molds prevented it from curing fully, which created some unwanted texture that did not allow our molds to align and close perfectly. 

Casting the Pieces

After removing the silicone molds from their 3D printed/CNC milled counterparts and pressing them together, there was a tiny hole at the tip of the king’s top because the hot glue ripped some of the silicone away. To close this hold for the casting process, we used a clamp to squeeze the tip shut. Our clamp for our first cast piece was too tight, resulting in an oblong shape, so we found a clamp tightness that closed the hole but resulted in rounder pieces. We put duct tape around the bottom of the mold to catch any spillover we had. We attached the rest of the mold with rubber bands. To estimate the volume of our piece, we used the SolidWorks calculator, which ended up being just shy of 40 mL. Unfortunately, some of the leaking we experienced resulted in some pieces being shorter than others.

 

After creating our 4 white chess pieces, we decided to create 4 green chess pieces with varying intensities of color. We sanded the edges where the molds met on each piece, as well as the bottoms so they didn’t wobble. Each of us cast 4 pieces, and after sanding, they look pretty nice!

Cost Analysis:

Cost Type	Cost	Price	Source	Quantity	Total
Material	PLA filament	$30/kg	Prusa	~320g/hour	$24
	4×4 plank	$3.56	Lowe’s	1	$5.48
	PlatSil 73-25	$20.63/lb	Brick In the Yard	1.1 lbs	$22.69
	EasyFlo 60	$9.87/lb	PolyTek	320 mL/0.77 lb	$7.60
	Green and white dye	$9.99/pack of 8 colors	Amazon.com	2	$2.50
Labor	CNC Mill Machinist	$25.10/hr	Indeed	1 hour	$25.10
	3D Printing Technician	$21/hour	ZipRecruiter	1	$21
	Molding and Casting Technician	$19.37/hr	Monster.com	4 hr	$77.48
	Quality Engineer	$32.50/hour	Salary	0.5 hours	$16.25
Overhead	CNC Mill	$50/hour	Wood-cutting CNC mill estimation	1 hour	$50
	Prusa 3D printer	$0.21/hour	Prusa Forum	2.5	$0.53
Design	Etsy	$1.80	Etsy	1	$1.80
Waste/Scrap	EasyFlo 60	$9.87/lb	PolyTek	40 mL/0.096 lb	$0.94
TOTAL					$255.37