Cost Estimate: $374.47

 

Materials: $180.97

1. PLA for 3D printed mold
   1. 3DPrinterOS Estimate: $1.03
2. Cardboard
   1. Used: One 12”x 12” cardboard sheet  
   2. Found: a 48”x96” sheet for $2.94
3. Wood 
   1. Used: One 2” x 4” x 11” Lumber
   2. Found: 2” x 4” x 96” for $2.82 At Home Depot 
4. Hot Glue Sticks 
   1. Used: Four Hot Glue sticks
   2. Found: 30 for $3.99 at Target
5. Platsil 73-25 Silicone Rubber 
   1. Used: 12 liquid oz per mold 
      1. Density of 24.3 in^3/lb which means we used about 2 lbs 
   2. Found: 2lb kit for $36.99 on Amazon with $20.49 shipping
6. EasyFlo 60 Liquid Plastic 
   1. 20 grams of each Part used per cast
   2. Totals 320 grams of Part A and Part B
   3. Found: 3.8lb for $45.99 plus $20.99 Shipping
7. Rust-Oleum Spray Paint
   1. Used: Green spray paint << 1oz
   2. Found: One 12 oz can for $3.98 at Home Depot
8. Rust-Oleum Black Paint
   1. Used: A dab of black pain << 1oz 
   2. Found: 1Qt. For $9.98 at Home Depot
9. Dye 
   1. Used: So Strong Green Dye
   2. Found: All color sampling pack for $31.77 with free shipping on amazon

 

Labor: $193.50

Time: 10 hours

Average machinist pay per hour: $19.35

 

For our final assignment, we were charged with creating chess pawns using the cnc machine, the 3d printers, and casting/molding. For the purpose of this blog post, “we” refers to Kaede and Eunice, as we partnered together on the first day to complete the final. The process to create the piece was a complex one: starting with a premade file from thingiverse, we were supposed to scale it and cut it in half. To create a positive, we had to add a backing with pegs and holes to both sides. One of these halves would be 3d printed while the other one had to be created with the carvey cnc machine, which required that we create a g code for the piece. After both the positives were created, we had to cast a silicone mold negative, and from here, 8 plastic positives.

 

Our first step was To choose a chess piece and download it from thingiverse. We chose a peashooter from the game plants versus zombies:

   

Satisfied with this part, we scaled it and 3-D printed the entire thing:

This was meant to help us understand the peace more, and see which parts would be difficult to cnc. We noted that the leaves that serve as the Pea shooters feet would not be able to be machined because of the overhangs that they presented. With this knowledge, we moved to solid works. Many teams did these steps in fusion 360, but since we both had more proficiency in solid works we used that software. We cut the piece in half and removed the leaves. We replaced the base with a solid disc and cut it in half. Then we created the two planes which would be the edges of our molds. We also added the pegs, holes, and a pour hole:

From here we went ahead and 3-D printed the 3-D printed side. While that was happening, we started our work on The g code for the machine side. At some point during this process, we realize that we had made the holes larger than the pegs, as they would be if the pieces were to be put together as they were: 

However, because we were creating a positive that would be used to make a negative which would actually have the pegs in holes, we needed them the opposite way. Thus, we had to adjust and reprint the 3-D printed part:

and adjust the G code. We had a bit of trouble finding a piece of wood large enough to make our machine side, so we ended up having to cut down the side of the solid Works part that was to be CNC machined:

This meant that the G code had to be reworked again. After this we finally got started on the carvey. The first issue we had was that we had placed the g code to be printed on the very edge of the wood:

This severely limited the way that we could clamp the wood, so we had to redo the G code to accommodate for this: 

Next, we had a problem with how thick the wood was, and had to make sure to place the bit right next to the homing button so that it would not hit the clamps on its way over. This being done, we got started on the cut. Everything looked good until 93% through the 3 hour job. Because the bit was shorter, as the carvey tried to get the lower parts of the design, the top of the bit started to get shaved off. For this reason we had to stop the carvey, resulting in a failed cut: 

From here we had to redo the g code with a longer bit. At this point we ran into another issue. The longer bit with the thick wood mean that the carvey could not home at all. Thus we used a planar saw to cut the wood down and tried again. This time, the carvey cut the job perfectly:

Happy with this we moved on to casting both sides in silicone: 

Both turned out very well:

The next step was to cast the plastic into the molds. We had several unsuccessful casts, and generally had lots of alignment issues. Here are some of the unsuccessful casts and the associate reasons they failed. 

Air bubbles: 

Plastic wasn’t rolled into the smaller parts of the mold: 

Pulled the mold out too early (too excited to see how the first dye job turned out):

Extreme misalignment:

When we finally had done enough pieces to have 8 decent ones, we moved on to sawing off the pour holes and using the belt sander to clean the bottom:

We also sanded the intersection of the two parts. Lastly, to make them look more like the original pea shooters, we spray painted them green:

And used paint to give some of them eyes: 

As our very last step we gave them a clear coat so they can survive handling. 

Overall, this was one of the most multifaceted and difficult assignments this year but was incredibly rewarding. We both learned a lot about the different processes despite having been introduced to them before, and were happy to be able to produce such a smooth final product and imposing line of pawns: