Introduction

Hey y’all,

We are Samuel and Steven, and for our final project, we decided to select a design for Steve from Minecraft to serve as the chess piece we create. Through this process, we implemented various fabrication and post-processing methods that we developed throughout the semester, including molding and casting, CNC, CAD, and many more. This blog documents the journey of our project from start to end, including the setbacks and successes.

File Setup

We began by selecting the file from Thingiverse and removing the excess features within it, which included a creeper and a skeleton from Minecraft. Then, to process the design, we used Meshmixer to cut the object in half, allowing us to use the CNC on it. We also used SolidWorks to generate the two halves of the project: one for the CNC process and one for the 3D printer. After printing the first version of the chess piece, we realized it was too small, so we scaled it to a factor of 1.8. A version of the chess piece, we realized, was too small. We selected the back half of Steve to be the part that the CNC would cut out, and the remaining half to be the part where the 3D printer would generate the positive part of the mold.

3D Printing

The first thing we did was to print the 3D part and make the silicon mold. We did so in class by constructing a cardboard box of indeterminate size and applying a large amount of hot glue to solidify the box, ensuring there were no gaps for the silicon to slip out of. After measuring out the correct ratio for the silicon base, we mixed parts A and B for approximately 1 minute before pouring the mixture into the box. When pouring into the box, we did so slowly and with caution to ensure that no air bubbles formed when the silicon solidified. 

However, after an issue arose during the CNC processing, which will be discussed later, we had to recreate the mold using the same procedure as before, but with a smaller 3D-printed piece.

Smaller than the first mold.

CNC Machining

Following the completion of the first silicon mold, we then proceed to cut out the negative part of the project using the CNC. We achieved this by uploading our file into V-Carve to generate a G-code, which enabled the CNC (Nomad Pro) to recognize the correct toolpath to follow. Once we began cutting, we realized that our original design was too wide, as it was wider than the block provided to us. To remedy this situation, we had to decrease the platform on which Steve rested. We used Solidworks to recreate the CAD files for both the 3D printed and CNC parts. For the CNC cut, we ran both a roughing pass (using a ⅛ in flat endmill) and a smoothing pass (using a ⅛ in ballpoint endmill) to create our CNC block.  This process went pretty smoothly and the only issues were the difficulty in getting all of our files set up properly.  

Once the CNC had cut out the corrected negative mold, we then followed the same procedure for pouring the silicon into a positive mold, but into the negative part of the CNC. And produced the negative silicon mold!

Curing Process

Now that both silicon molds were complete, we were able to start the curing process and create our chess pieces. In class, once we removed both silicon molds, we realized that our molds were made out of two different types of silicon, such that one mold was noticeably firmer and resistant to pressure than the other. Although it presented a challenge, we resolved the situation by attaching two thin pieces of plywood to the exterior of both molds to prevent deformation during casting, and we secured them in place using rubber bands. We followed the correct procedure outlined in class for formulating the proper volume of the polyurethane mixture. Once we determined that we needed 23 milliliters of both Part A and Part B, we mixed the two substances and poured them quickly, as the mixture cured incredibly rapidly. Our first cast chess piece was flawed; we had forgotten to dry the inside of the molds before pouring the polyurethane, resulting in air pockets within the piece.

Once we realized the error of our ways, we quickly addressed the issue and created another piece that turned out better, but still resulted in many air bubbles on the surface of the cast. To combat this, we decided to swirl the mixture around within the mold to ensure all surfaces within the mold were in contact with the polyurethane. This proved to mitigate the problem, but it was not enough to eliminate the issue. However, we found that swirling the mixture within the mold, frequently and evenly, yielded the most favorable results.

Once we had learned from our errors, we quickly began mass-producing our four chess pieces, all with different colors. We did this by mixing the dye when we stirred together parts A and B of the polyurethane. These pieces represented a significant upgrade from our initial attempts.

Final Results

After we finished casting all four pieces, we still had to post-process and touch up some faulty parts. First, we achieved this by removing the excess polyurethane at the point of connection between the two molds, specifically at the thin lips. We also removed the fill hole we created at the bottom of the piece and finally sanded down any uneven, patchy, or otherwise unattractive parts of the chess pieces. We made use of the bandsaw and the belt sander to help with post processing.  Once we post-processed everything, we had created four identical (almost) Steve chess pieces!

Cost Analysis

Labor:

Labor: $145

20 hours (At Texas minimum wage) = $145

Equipment: $25

Maker Space One-month membership, includes all the tools and machines (CNC and 3D printer) used to construct this project, and scrap material such as plywood, rubber bands, cardboard, popsicle sticks, plastic cups, and hot glue sticks. $50 per month, use for half a month.

Materials: $34.69

PLA: 50 grams @ $0.02 per gram = $1

Silicon (Parts A and B): 5 oz @ $1.95 per oz = $9.79

Polyurethane (Parts A and B): 8 oz @ $2.23 per oz = $26.78

Dye: ~10 millimeters @ $0.00837 per millimeter= $0.09

Wood Blocks: 2 blocks $5.97

Total = $204.69

Conclusion

Through this final project, we learned many things regarding file setup and preparation, creating molds and casts with various substances, enhancing our existing skills developed earlier in the semester, and further developing our soft skills. We did not anticipate that the correct setup and preparation for this file would consume most of our time compared to the rest, but we learned a great deal from that experience, and we are pleased with our final results. 

Throughout the semester, EDES 210 has taught us the prototyping and fabrication methods advertised in the class description, while also introducing us to much more. EDES 210 was filled with numerous grueling setbacks, but at the end of all these setbacks were learning opportunities that propelled our knowledge and understanding to a new level when it comes to designing, manufacturing, and processing a given project. We are both extremely grateful for all the learning opportunities EDES 210 has provided us and will definitely utilize them in future endeavors here at Rice.

 Pictures of Cleaned Workspace