Our Chess piece project’s original file is download from:
https://www.thingiverse.com/thing:1291983
We decide to make a cute fox because we have Fox in our team.
The primary scale was set 66% to fit a proper size that is not too big for the material size or too small for the details to be shown. The first 3d-printed model was only 40% in size so we made that change into 66%.
For gate 1, we need a positive 3d printed mold. Because the 3d-printed side can show more details, we 3d printed the front half for the fox face’s details.
With Meshmixer, we cut the fox into halves, reduced the angles into 10000, and downloaded them separately.
We used the 3*4 inches mold base file on canvas, and combined the two parts with Solidworks. Because the fox’s base is not flat, we create a hole at the bottom, which is also a positive part in this file.
Then it was the step to make a silicone negative mold.
We used hot glue to fix the cardboard around our first half mold. It is important to check there is no gap between the cardboard so that the liquid will not leak off, so we used more than enough glue around the cardboard and the mold.
We calculated the volume of our file. It was about 28ml, so by subtracting the positive parts we need 198ml of silicone. We measured 99ml of part A with weight of 123g. Then we measured 123g of part B. Then we stir part A and B together, pour on the positive mold, and wait for several days for the silicone to be cured.
For gate 2, we created the back half of the fox with Meshmixer and Solidworks. This mold should be CNC cut, and their should be first a rough cut and then a finish cut, otherwise the cut will fail.
We chose to use the 1/8′ end mill first, but the time estimation was 6 hours, so we chose 1/4′ end mill. Then to make More detail we tried to use 1/16′ end mill for the finish cut. However, accidentally the mill was broken because the level cut by 1/4′ mill was too steep. So we finally used 1/8′ end mill for finish cut.
Similarly, we added cardboard and hot glue to the mold and used the same amount of silicone for the negative part. However, there was a problem that the negative mold was too sticky after a 2-day curing. It might be caused by wrong measurement of the ratio of part A and B, but we don’t have time to remake another.
We immediately started to make a test piece of the final PU chess. The total volume should be around 54ml, so we measure 27ml of each part A and B. However, some liquid accidentally leaked off, so even the bottom was not filled. Also, there were some air bubbles on the surface. We learned that we should move our negative mold around after we pour half of the PU inside the mold. Then we pour the remaining. This is a way to reduce the surface tension of the liquid to make the mold completely filled.
After 3 more days curing, the CNC negative mold was cured and no longer sticky. We started to make the four formal chess pieces. To ensure the volume, we measured 30ml of each A and B. We chose to use different colors when mixing.
This time there was a hump at bottom of each chess after curing, so we used the bandsaw to cut this part.
Workspace when finished:
COST ESTIMATION:
Material:
from Amazon:
Silicone: $33/37oz * 246g = $7.73
PLA: $15/kg * 80g = $1.2
PU: $135/15lbs * 60ml = $1.43
1.5′ thick Wood: $7
sandpaper: $10/12 *2 = $1.67
Machine:
CNC: $100/h * 1h = $100(https://www.sigmatechnik.com/cnc-factory/the-hidden-costs-of-renting-a-cnc-machine-how-much-does-it-really-cost?)
3d print:$299/month (https://engineering-update.co.uk/2021/11/01/how-much-does-it-cost-to-rent-a-3d-printer/)
$299*1/240 = $1.25
Labor:
Houston Average wage 2 * $30/h * 5h = $300
Total：¥420.28
