Project Overview:

For our final assignment in ENGI 210 we were assigned with making a silicone mold and casting 8 identical chess pieces. To do this we had to pick a part off of thingiverse and then created two halves of a positive mold, one was required to be 3D printed and the other CNC routed. This submission is for both Leticia and Walsh and we worked in a pair for this project.

 

The Process:

We started by picking a design for our chess piece. We thought about doing a cinder block, a penguin or a frog. We ended up 3D printing both the cinder block and frog to see which one we liked better.

When we printed the frog we sliced it and scaled it to twice the original size. 

Printed cinder blocks

Printed frog

 

We ended up choosing the frog!

We downloaded the stl file and uploaded it to meshmixer, cut out shape in half and reduced the triangle count of the mesh. Then we uploaded this new final in Solidworks where we added a base, two pins, two holes and an air hole.  

We uploaded this new file to the printer, uploaded and printed it. 

We did this same process with meshmixer and solidworks for the back half of the frog and changed the pins so that both halves would fit. 

Printed pieces (only using the bottom, top is just for visualization)

 

We took this back half file and uploaded it to Vcarve. Here we changed our woodstock size and added three toolpaths: Roughing, Finish, and Finish final. We opened this file on the OEDk computer and sent it to the Nomad 3. 

CNC file prep

CNC physical prep

 

After probing the Nomad we ran into the error Switch Limit which we later found out was a loose magnet. Then we also ran into the issue of it being very loud and moving at too fast of a feedrate. After troubling shooting with the help of the TA’s we got it to work well.

CNC

 

After we completed all the toolpaths of the file, we sanded the wood piece. 

Finished CNC piece

Now that we had both our 3D printed frog front and CNC frog back, we created a mold. We a frame made of cardboard around both pieces to create border to fill into. We made sure this box was sealed properly with no leaks using a good amount of hot glue. For the mixture we had to get the amount of Volume of silicone needed. We calculated this by the volume of the box we were creating, which went about a cm above the top of our shape, and subtracted the volume of our shape. This gave us a volume of 9.25 in^3 which converted to 152 mL. We measured part A and B by weight separately 1:1. Then we poured A into a cup and then B, stirred well and then poured our cardboard borders. 

Pouring silicone molds

Let molds sit

After waiting 6 hours for both molds to set, we carefully removed them. To attach them together we used the pins as guides and then two thin slats of wood and rubber bands to create compression. We had to ensure that our casting would be tightly secure.

Rubber band the molds together (ready to pour)

 

To create our casting mixture we measured 1:1 ratio of the parts of liquid plastic. We poured 25 mL of Part B liquid plastic, added some polycolor dye and then added 25 mL of Part A liquid plastic which made the volume of our frog chess piece. We did this 9 times, perfecting our pour to get all the details of the frog feet and testing out different colors and combinations.  Each cast took about 9 minutes to dry. 

  post pour (waiting 9 minutes)

Finished Frogs!

Reflection:

Things we would like to work on in the future:

• All of our casts end up a tiny bit overlapped and not perfectly smooth. We’d like to explore how to solve this/make it less noticeable
• Would have liked to explore creating a base for our piece included in the mold
• Experiment with colors a bit more

This project combined the skills we developed from our previous three. Using the printer, the CNC machine, and casting molds. Overall this was a really fun project to work on and we both had a good time. Despite sometimes running into problems with the router, or making a mess while casting molds, the entire process was relatively smooth and we had no real issues. We really had to plan our piece out ahead of time and used a total of 4 different file softwares to make everything!

Cost Estimate:

• Material:
  • wood: 4$
  • PLA (printer plastic): 3$
  • Platsil 73-25 Gallon Kit: 249$
    • Used ~200 mL: 0.0528344 X 249 = 13.2$
  • EasyFlo 60 Casting Resin (Gallon Kit): 109$
    • Used ~200 mL: 0.0528344 X 109 = 5.76$
  • Mold Release Spray: 6$
  • Cardboard: free scraps!
  • Dye: 16$
  • Misc (popsicle sticks, plastic cups, etc): 6$
• Time Cost
  • 8hr X 2 X 15$ =240$
• Machine Overhead
  • 150$
    • hours spent printing/CNC

TOTAL: 443.96$