First, we looked on Thingiverse for a chess piece and we found a squirrel knight with a helmet that we thought was the cutest thing ever. After getting it checked, we 3D printed it to scale at 2.5 inches tall. 

Next, we opened the .stl file in mesh mixer to cut the squirrel in half in order to start creating the 3D print vs CNC halves. In order to make the creation of the top of the helmet easier, we sliced the squirrel down the middle just to the left of the helmet. The side with the helmet would be 3D printed, and the side without the helmet would be CNC machined. 

Then, we used the half squirrel .stl file and started to work on making the base using solidworks. We sketched a square around the squirrel and then added in equally spaced holes and pegs which would be useful for the casting steps later on. We repeated this process for the other half of the squirrel. 

 

Once the file was ready, we 3D printed the squirrel half with the helmet.

After, we calculated the amount of silicone we would need to pour into each half in order to make the negative molds of the squirrel. Calculations:

3d print dimensions: 2.939 x 2.581 x 2.094 in

Volume 3d print box = 15.885in^3

Volume 3d print squirrel = 1.727in^3

Volume silicone needed = 14.158in^3 = 232mL

To prepare the 3D print for the silicone pour, we hot glued a cardboard box around it and applied glue along all of the edges to make sure none of the silicone would leak out. We measured out 116mL for both parts of the silicone, mixed them, and poured it into the box to let it cure for 24 hours. 

While the silicone was curing, we switched over to making the CNC squirrel half. We took the .stl file we made in solidworks and imported it into VCarve. We set the dimensions of the 3D part and placed it in the center of the wood block. Then we chose the drill bits and created the roughing (¼’’ bit) and finishing (⅛’’ bit) toolpaths. 

Once the file was done, we exported the G-Code and uploaded it to Carbide Motion. We followed the steps to set up the Shapeoko and attempted to secure the 3.5 x 6 x 1.5in wood block to the platform. We struggled to place any of the clamps on top of the wood to hold it down so we used clamps along all 4 sides. Once the cutting started, the wood block was dislodged so we had to start over. We attempted to secure the wood block again, but it was rocking back and forth a lot during the roughing cut, so we stopped and reached out for help.

 

Professor Bisesti kindly offered to help us secure the piece to the Shapeoko, however even with her help, we were unable to fully secure the wooden blocks (this is most likely due to the shape of the clamps which are not well-made to secure a wooden block of this thickness (1.5’’). After several frustrating attempts, Professor Bisesti suggested that we switch to learning how to use the Carvera.

We pulled out the instruction manual, and a few YouTube tutorials, and set up the VCarve file on the computer attached to the Carvera. Since the Carvera did not have many larger drill bits, we completed the roughing step using the 25mm flute drill bit.

 

This smaller drill bit gave us enough detail in the carved part, that we actually didn’t even need a finishing toolpath step.

The Carvera finished creating the piece, and then we attached cardboard around the edges of the cut to prepare for pouring in the silicone.

After the silicone cured on the CNC cut half, we de-molded it and noticed that the 3D printed half and the CNC half looked suspiciously different. Something had gone wrong with the scaling of the CNC half (possibly during the SolidWorks prep step), and it was at a slightly smaller scale compared to the 3D printed half.

In light of this little hiccup, we persevered, after all, we are engineers. We lined up the silicone molds as best we could (trying to keep the squirrel’s front facing features aligned), and rubber banding the negative silicone molds together, while using popsicle sticks to level out the size difference between the two mold sides. 

We mixed the polyurethane parts together (1:1 ratio) with a little bit of dye and poured the polyurethane into the pour hole, waiting approximately 15 minutes before de-molding.

This worked surprisingly well on the very first attempt! And we were quite pleased with the outcome! We continued following this alignment, rubber band and popsicle stick placement for each new piece. The results were fairly consistent, and we are super happy with the finished products!

 

After assessing our squirrel pieces further, we realized that this scaling difference between the two halves can be seen as a beautiful mistake, which can bring new meaning to the finished product.

The side with the knight helmet (created by the 3D print mold) is slightly larger, showing how the squirrel feels big and proud while he is in his uniform and has a strong purpose in life. However, the side without the knight helmet (created by the CNC mold) is slightly smaller, showing how without his helmet, he loses his purpose and consequently stands a little lower, and feels a little smaller.

Cost Analysis

Cost Type	Cost	Price	Source	Quantity	Total
Materials	PLA Filament	$13.99/kg	Amazon	1	$13.99
	Wood Block (3.5’’x6’’x1.5’’)	$19.99/6-pack	Amazon	1	$3.33
	Silicone	$40/ 84oz	Amazon	16 oz	$7.62
	Polyurethane	$37/ 32oz	Amazon	2.5oz	$2.89
Labor	3D printer operator	$19/ hour	Zip Recruiter	3 hours	$57
	CNC operator	$22/ hour	Zip Recruiter	7 hours (this is because we are novices and wasted lots of time doing things incorrectly at the start)	$154
	Casting	$18/hr	Zip Recruiter	4 hours	$72
Overhead	CNC machine	$100/hour	ClickLease	7 hours	$700
	3D printer overhead	$10/ hour	Reddit	3 hours	$30
Total					$1,040.83

The time we spent with the CNC machine inflated the cost of this project. We were learning and making a lot of mistakes. In the future, this would cost much less because the overhead to use the CNC would be reduced.

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