For the final assignment, I applied learned knowledge in 3D shapefiles and advanced manufacturing techniques to create four mold and cast chess pieces. The mirror positives were produced using CNC machining and 3D printing.

First, I found a 3D file of a chess pawn piece uploaded by user Tetralite https://www.thingiverse.com/thing:378322. I downloaded the file and proceeded to scale it up by 1.5x and 3D print using the Bambu machine. Afterwards, I uploaded the pawn piece 3D file into Meshmixer to preprocess. I sliced the shape in half by using the  “Edit” → “Plane Cut” feature and since it is a symmetrical object, I discarded the second half and saved it as a binary file. I made sure to reduce the mesh, keeping it at around 1000 triangles on the Triangle Budget.

To further preprocess, I uploaded the binary file into Solidworks where I would add the mold base provided in Canvas to the half pawn piece. This is in order to add geometry that will allow for cast pouring and molding. Using the “Scale” and “Measure” features, I scaled the object up by 1.5x to match my  previously printed 3D object. I made a note of the dimensions of the object as well. Using the Plug and Play method provided in the homework instructions, I created an assembly of the half pawn piece and the mold base using the “Mate” feature. Since the base was open and flat, I concluded that adding a pour hole was not necessary thus, I proceed to save the file as an stl. After preprocessing in Solidworks, I proceeded to 3D print the object using the Bambu printer, creating the first positive mold.

Next, I created a negative silicone mold from the 3D printed assembly. First, I created a box of indeterminate size around the shape using four cardboard pieces and a hot glue gun. Once I determined that the box was sufficiently sturdy and water-tight, I proceeded to mix the silicon together. In order to determine the amount to use, I measured the dimensions of the box: length (9 cm), width (6 cm), and height (height was determined 1 cm above the highest point of the shape – 2.9 cm). I obtained the volume of the box this way (156.1cm). I determined the volume of my 3D printed pawn piece by using the density-volume equation. Knowing that the density of PLA filament used is approximately 1.25 g/cm3 and I measured the mass of the piece using a scale (26g), the volume was determined to be 20.1 cm3.

The following calculations were made to determine the amount of silicone Parts A and B to pour. Part A was measured by volume and Part B by weight using a scale.

Once I measured and mixed both parts, I poured the mixture into the box and left it to set. Knowing that silicone takes about 14 hours to set completely, I returned to the OEDK 24 hours later to retrieve the mold, making sure to clean up the area as well.

The next step was to create the CNC mirror positive mold. Using the Nomad3 computer, I uploaded the assembly file into V-Carve and set up my workpiece according to the homework instructions. I measured my wood pieces and imputed  the dimensions in the job setup tab (7.5” x 3.5” X 1.5”). I adjusted the position and scale of the object by carefully aligning the pawn piece-mold base assembly on the wood work piece and zeroing the depth below top. To create the toolpaths, I adjusted the roughing toolpath by importing the #102 tool and the finishing toolpath by importing the #111 tool. I saved they-code for both toolpaths into a single file and prepared to cut.

Once I imported the g-code into Carbide Motion in the Nomad3 CNC machine, I set up the machine by clamping my wood piece, fastening the ⅛” Ballnose Endmill placing the homing device on the bottom left corner, and probing the machine tool. Once this was complete, I selected “run job” and began cutting the shape. After the roughing toolpath was complete, the machine prompted me to switch out the endmill tools. I thereby fastened the 1/16” Ballnose Endmill and continued the cut. The cut took 48 minutes to complete.

I created a cardboard mold box around the shape of the cut out assembly in the wood. Afterwards, I poured the silicon mixture onto the shape using the calculations that I obtained earlier. After 14 hours, the silicone mold was set and I proceeded to remove it (with great difficulty and help from TA Luke). One lesson learned here is to apply clear coat spray into the shape prior to pouring the silicone in order to allow for easier release of the mold.

After I had both molds, I assembled them using the opposing plugs and holes, as well as rubber bands to make a tight, snug single mold. I made the polyurethane molds by combining the Part A (along with 2-3 drops of the chosen dye color) and Part B liquids into a silicon measuring cup and subsequently into the combined molds, making sure to avoid spills, air bubbles, wobble, or uneven surfaces. The polyurethane took about 4 minutes to set each time. I then made 5 chess pieces of colors white, pink, brown and black. Once removed from the molds, I removed the imperfections and dross. I also sanded the surfaces of the pieces using 220-grit sandpaper, making sure to avoid over-sanding.

 

Some problems encountered during this assignment were great opportunities to do better in the future. One instance is that with future CNC machining projects, if precise dimensions are required, I would scale my object up slightly. Since I did not do this for my final homework, the CNC negative mold was slightly smaller than the 3D silicone mold. Further, some waste was generated since I poured some pieces which were discarded due to staining by unwanted dyes. I also poured some pieces with inconsistent shapes due to spilling from not fastening the silicone negative molds tightly enough. In the future, I will apply more careful consideration prior to pouring the molds and use materials more judiciously.

 

The project cost about $115 to produce, including labor and materials. Looking forward, in order to cut some costs, I have learned that precise measurements and judicious use of materials are important to cast and mold projects.

Cost Model:

Cost Type	Cost	Price	Source	Quantity	Total
Materials	Bambu PLA filament (basic matte)	$19.99	Bambulab.com		$1.99
	Platsil 73-25 Silicone kit	$305 per 16lb kit	Ploytek.com	24 oz	$28.6
	Polyurethane casting kit	$40.99 per 30 lb kit	Amazon.com	12 oz	$8.2
	Hot glue sticks	$1.27 per 10 sticks bag	Walmart.com	3 sticks	$0.381
	220-grit sandpaper	$2.69	Amazon.com		$2.69
	Popsicle sticks	$.97 per 50 pack bag	Walmart.com	10
	1/2 in. x 16 in. x 4 ft. Softwood Boards	$15.97 per board	HomeDepot.com	1 3.5” x 7” piece	$5
Labor	Prototyping Engineer (Thingiverse user: Tetralite)	$10			$10
	Prototyping Engineer (You!)	$10/hr	Self	10 minutes	$1
Overhead	Facility Cost (Machine Time)	$5/hr	OEDK Bambu 3D printer	0.5 hrs	$2.5
	Facility Cost (Machine Time)	$7.50	OEDK Nomad3 CNC machine	2 hr	$15
	Quality Control	$5
Design	Engineering and Development	$10/hr	Self	4 hrs	$40
	Iterations	3			$20
Misc.	Waste and Scrap				$15
Total					$115.361