Picking a design
Both of us being mechanical engineers with SolidWorks experience, we decided that it would be fun to design our own chess piece. We started out wanting to do a geometric design, but got inspired after seeing this spiral design on Pinterest:
Based off of this, we made our piece:
Prepping the files
We prepared the top and bottom as separate pieces. first, we split them in half on meshmixer, then added a base and pegs/holes in SolidWorks. In hindsight, we didn’t need to use meshmixer at all; our part was a SolidWorks file to begin with and could have been cut locally. after printing the front half, we realized that we dimensioned our pegs/ holes wrong. Holes on the positive have to be small and pegs have to be big so that they can fit when reversed (making smaller pegs and bigger holes).
Then, we imported the parts into fusion 360. we were hoping to do it on SolidWorks but the tool directory and interface were not intuitive and having step by step instructions was too tempting to pass up. in Fusion, we set up our tool path correctly, or so we thought…
Carvey chaos
After waiting an 1 hour 45 minutes, the rough cut was complete and looked pretty good. Then, we started the smoothing cut. The bit immediately started hitting the edge and wrecked some of our holes/pegs. Then, we paused the cut, added a bounding box, and started over. It did work, it was just 100 times more ugly than the rough cut.
So we started over and stopped at the rough cut, not wanting to mess up another adequately smooth surface.
molding + casting
First, we made our molds. To keep the silicone from oozing all over the table, we made cardboard boxes around our positive halves. We then poured in the silicone mixture and waited a day.
Then, we poured in the plastic. Unfortunately, we ran into two problems:
- the rough cut was bigger than the 3d printed half, making an obvious divide between the two halves. We were originally planning to do a second attempt of the smoothing pass, but since the carvey was down that was no longer an option for us.
- The geometry of the part was such that air bubbles formed easily and frequently in the narrow edges of the piece. After making six pieces, we decided that any more would be a waste of materials, despite there still being prominent air bubbles in all of them.
We did try pouring in extra plastic into the mold and then putting the piece back in to fill out the bubbles but that was unsuccessful (see below)
We picked the best two pieces to present as our final product:
I do wish we could have gotten the casting to be cleaner. The air bubbles are very noticeable, as well as the transition to the CNC half. A few of the other groups used a dremmel to smooth out that edge, which worked quite nicely. We also could have made our geometry thicker to decrease the number of small pockets for air.
cost analysis
3D printed positive half with base:
⁃time: 2hrs
⁃2x prints: $1.62 in total
CNC Machine:
⁃time (preparing file): 2hrs
⁃1x unsuccessful carving: 2hrs
⁃1x successful carving: 2hrs
Silicon mold:
Considering two full bottles of blue+yellow weigh about 7.5kg and cost approximately $300, the 290g we used to create two halves of our mold amounts to $11.60.
⁃material cost: $11.60
⁃time: 30mins
Casting material:
The liquid plastic set <https://polytek.com/products/easyflo-60-liquid-plastic> we used costs $132.88 for 15.2 pounds (6894.6g).
Each of our casted pieces weighed about 26g, which amounts to $0.50 per piece.
We made 6 attempts at casting in total, which cost $3.00 in total.
⁃material cost: $3.00
⁃time: 1.5hrs
In total, our project took approximately $16.22 in material cost and 10 hours of labor. Applying a rate of $20/hr, the chess piece project cost approximately $216 in total.
