For the final project of the course, Callum and I worked to mold and cast 8 chess pieces of a blobfish. One side of the piece was molded from a 3D-printed source, and the other was sourced from a CNC-machined part in wood.

PHASE 1: dESIGNING THE PIECE

The first gate of the project required for a 3D-printed chess piece to act as a reference for what the final product may be. As such, Callum and I had to brainstorm a design for the piece. To keep in with the theming of Callum’s projects this semester, our piece was going to be a pawn with its top being a blobfish. The model used for the top was sourced from Thingiverse and imported as an STL into SolidWorks. Callum created an assembly of the first design with a base piece they designed to create a complete part to 3D print. They pointed out some issues with importing the STL file, but in the end, it worked out.

The part design in SolidWorks

PHASE 2: 3D Printing the reference piece

As stated, Gate 1 required a 3D-printed whole piece, so with our model done, we went to 3D-print the piece. We used one of the Prusa machines to FDM our model.

Below are three views of the 3D-printed piece.

After meeting with Dr. Wettergreen for the Gate 1 check, he noted that the main body of the piece was not the most proportional, so that piece was then redesigned to be more proportional before moving on to creating the molding templates.

Revised blobfish piece

PHASE 3: Preparing mold positive models

To create the molding positives, the process was split into two. One half of the piece would be created using 3D-printing, and one would be CNC-machined. To do this, some preparation had to be done with the model.

To establish where the model would be split was dependent on how the piece is structured. Upon analyzing our piece, it was decided that the tail would be 3D-printed, and the face CNC-machined. This decision was based on the tail having overhanging geometry that would not allow for a proper CNC cut.

Our STL file would then be split in half using MeshMixer. There were some optimization issues with the program, so it was a bit of a challenge getting the proper polygon count to import into SolidWorks.

These halves would then be implemented into SolidWorks to model the surrounding base for the piece in order to mold it. With Callum and I both having CAD experience, we both made the surrounding piece from scratch, with me working with the face and Callum with the tail. The process went well in creating the models.

After some comments, this base would be reduced in height to be more compact. Furthermore, Callum pointed out that the pegs and holes needed to be repositioned so that the molds could meet whenever created, so that was also adjusted.

PHASE 4: Process for 3d-pRINTED MOLD

For this phase, the base with the tail side was 3D-printed using a Prusa FDM printer to create the positive for the mold.

From there, the piece was used to create the negative silicone mold for the 3D-printed side. To complete this process, a cardboard box was created around the part to house the silicone mix that would be poured over the piece. It was recommended for the silicone mix to fill about 1 centimeter above the piece. The volume of the piece and the box were calculate to get the proper measurement for the pour.

The silicone mix was made with a 1:1 Part A and Part B ratio by weight, so conversions from the volume to the weight were done to mix half and half of each. Part A was poured to a certain weight, and then Part B was poured on top of A to contribute the other half of the weight amount. The two parts were mixed well and then poured into the box to cover the piece.

After the pouring, the part was left to set for some time, and then de-molded. The mold came out very well! Below are some images of the mold.

PHASE 5: process for CNC mold

For Gate 3, the second negative mold would be created from a CNC-machine half. To do so, we had to CNC the part on the Shapeoko XXL. This involved importing the part into V-Carve and setting-up 3D-tooling paths to carve out the piece.

In V-Carve, the front-side STL part was imported and proportioned. There were some slight issues in setting the cutting plane, but that was later adjusted.

Callum set-up the plan of one rough cut using the 1/4″ end mill, and a smoothing cut with the 1/8″ ballnose mill. However, they were noticing our smoothing cut estimated at around 2.5 hours, which would not be viable given CNC reservation limits. Here, Cris helped in pointing out that the RPM of the spindle and amount of material coverage of the cut could be changed, which we did to reduce out estimated time to around 40 minutes.

Below is the model in V-Carve’s preview:

In our first attempt to carve out the piece, the roughing path went well, but there was not enough time time to complete the smoothing pass. I would come in later to run the smoothing pass, but I would run into the issue of the homing not being accurate enough to complete the cut. This resulted in the mill cutting into the piece. It was deduced that the roughing and smoothing cuts would have to be done in one sitting to avoid having inaccuracies in re-homing during separate cuts.

Another attempt was done, but the CNC machine turned off before the smoothing cut was completed as we ran out of time due to an issue with securing the main piece. Because of this, we developed a way to secure the piece using the clamps and other pieces of wood.

In-between planning another CNC session, Callum noticed that the sizing of the piece was not flush with the 3D-printed piece, so they re-sized it before making what would be our final CNC session as the part would be completed successfully.

After this part was cut, the same mold-creating process described in Phase 4 was followed with the silicone materials at a 1:1 Part A a Part B ratio. There were small adjustments to the volume calculations due to the different heights of the parts, but the part itself still contributed half a fluid ounce. With that, the negative mold for the face side was created.

PHASE 6: molding and casting the pieces

The final part of the project was to mold and cast the pieces. The goal was to create 8 pieces, 4 white and 4 dyed.

To do this process, urethane liquid plastic would be mixed in two parts to the volume of the piece and then poured into the mold to cure. For our specific piece, the tail and fins were of some concern due to their size and position in the mold, but Dr. Wettergreen noted that a part of the liquid plastic could be poured into the mold, and the surface tension broken up with a thin tool before the rest is poured in.

Callum also had the idea to let these sensitive parts cure before pouring the rest of the liquid, so they ran a small test and noted how a solid was still created doing this process. Therefore this is what we ended up doing for each piece.

Each mix of Part A and Part B liquid plastic would be estimated at around 1 fluid ounce as quite luckily the volume for the piece was 1 fluid ounce, and each part was left to cure for about 10 minutes.

Interesting things were noticed during this process. First, the exothermic process of the liquid plastic was interesting to feel as the molds and parts were noticeably hot. In terms of color, the pre-cured parts resulted in a darker shade of color than the remaining piece, so it resulted in some type of marbling color, and the material properties also changed slightly by become more transparent and soft. A tactic we learned when demanding was to bend the mold outwards strongly and have someone pull out the piece. This allowed for the smoothest exit for the casted piece.

Some issues noticed with some parts were detached back fins, so for about 2 pieces, they had to be glued on. Furthermore, some pieces were misaligned in the mold, but it was nothing too extreme. Overall, the pieces came out well!

Phase 7: Project completion

After the pieces were created, Callum and I worked to post-process them. To do so, 220-grit sand paper was used to sand down rough edges on the pieces, which was an interesting process at times due to having to distinguish between a rough edge and misalignment of the halves.

It was noted too that some pieces did not stand straight due to excess material at the base. To level the pieces, the belt-sander was used to flatten the base.

With post-processing done, the pieces were all complete! Bellow are photographs of the final 8 pieces.

PHASE 8: Reflection and cost estimate

This final project was a very neat send-off for this course. The concept and the process for it was very interesting to work through, especially with applying a lot of the skills we learned over multiple projects. I feel like it was a really good test of those skills and to also learn new ones, such as working with creating the molds. Callum also noted the project was a lot of fun and a great learning experience for their skillsets, albeit the process was rather time-consuming. Furthermore, discovering thing such as material properties was very fascinating too.

Overall, we thought it was a great project to work on with a very rewarding result in these 8 chess pieces. If we were to improve on our parts, we would try to better align the molds to avoid misalignment, and to try to aim for a more consistent look to the die for at least some pieces.

The following is an estimated cost of the 8 blobfish chess pieces:

• Material: 1kg PLA Pristine White spool (by Prusa): $29.99
• Overhead cost of Prusa machinery (Prusa Blog): $0.21/hr x 2 hours = $0.42
• Labor: $21/hr (national average for a 3D-Printing Technician by GLASSDOOR) x 2 hours = $48
• Material: Wood (full plank by Home Depot) $3.00 estimate x 4 = $12
• Labor: $23.32/hr (national average for CNC machinist by BLS) x 6.5 hours = $151.58
• Overhead Cost: $35/hr (for a 3-axis CNC Machine by RapidDirect) x 6.5 hours = $227.50
• Material: Silicone rubber: $1.56/fl-oz (Amazon) x 26.50 = $41.34
• Material: Urethane liquid plastic: $1.58/fl-oz (Amazon) x 8 = $12.64
• Labor: $17.50 (national average for Modeler, Shaper, Caster by Payscale) : x 4 hours: $70.00

The total cost of the 8 chess pieces was $593.47. To reduce this final cost of the pieces, a reduction of labor costs could be beneficial due to their high cost contributions. This would mean being very efficient with labor.