Molding and Casting – Fingers
This week in BIOE 555 students were tasked with creating a wall hook of their chosen phalange. This process required us to make a mold of our finger, cast it with plaster of Paris, and customize it.
To make the mold, I measured and mixed 33g of alginate powder and 125 mL of water. Using a popsicle stick, I made sure the alginate powder was fully incorporated into the water.
Figure 1. Scale and Materials for Measuring Alginate Powder and Water.
Figure 2. Plaster of Paris Used for Casting.
The first time I tried this (as a whole class outside in partners), Gabby and I took too long stirring our mold mixes so parts of the alginate cured before we dipped our fingers in. This resulted in a crappy mold that broke after pouring the plaster of Paris in to cast the finger. This iteration looked like a weird rock or some Pompeii ash mummy relic. This trial also broke because the plaster was very soggy and gross from sitting in the alginate slurry so I do not have any photo documentation of this result. See Figure 3 for the WRONG consistency (chunky like oatmeal) of the alginate and water mixture for the mold-making process.
Figure 3. Demonstration of First Attempt.
Figure 4. Resulting Alginate Mold.
The second time around, I used more alginate powder to 125 mL of water, mixed it properly, and sat with my finger in the alginate to impress for about 6-7 minutes. After I felt some resistance when moving my finger, I carefully removed it and started mixing two parts plaster of Paris (Figure 2) with one part water. I poured this plaster into the mold and set my screw into where the base of the finger would be. I left this to dry overnight at the OEDK. This attempt was successful and is shown in Figure 5. The molding and casting process captured my finger in great detail and I could see most of my fingerprint. However, the alginate mold broke while I was removing this pointer finger. Since we had to make two identical fingers, I decided to just make another mold, this time, of my middle finger. These two casts are demonstrated in Figure 6 and have great details like the pointer finger.
Figure 5. First Successful Finger with High Resolution.
Figure 6. Successful Middle Finger Casts.
CUSTOMIZATION
To add some pizzazz to my fingers, I spray-painted them purple and I planned to superglue a fake nail on my plaster nail. I sadly forgot to grab my fake nails from home (which is a couple hours away…) so I just did a second coat of color on each finger to prepare it for grading. At this point, I had lost the 3D-printed supports for the screw so I had to screw the fingers into popsicle sticks to make sure they could dry correctly.
Figure 7. Spray painted Fingers (Middle fingers are Purple and Pointer Finger is Silver).
Figure 8. Spray Painted Fingers Drying After Second Coat on Popsicle Sticks.
Figure 9. Final Product – First Cast (right) and Second Cast (Left)
Figure 10. Clean Work Space.
DISCUSSION
Overall, this was a simple, relatively quick process that was able to capture my finger in great detail. Kind of strange to see your disembodied finger on a screw but it was fun to play with the goop required to complete this project. I was able to leave the fingers to dry after a quick but often messy set up so this project allowed for some flexibility in my schedule. The first finger came out more detailed than the second since the alginate is fragile once dry and can sometimes tear away or break apart as the first cast is removed. Both first casts of my pointer and middle fingers captured great details in my finger.
COST ANALYSIS
| Cost Type | Cost | Price | Source | Quantity | Total |
| Materials | Alginate Mix | $11.99 | Hobby Lobby | 1 bag | $11.99 |
| Plaster of Paris Mix | $7.99 | Michaels | 1 tub (4 lbs) | $7.99 | |
| Spray Paint | $10.99 | Amazon | 1 can | $10.99 | |
| Popsicle Sticks | $0.97 | Walmart | 1 bag | $0.97 | |
| Silicone Measuring Cup | $8.99 | Amazon | 2 cups (1 set) | $8.99 | |
| Scale | $9.92 | Walmart | 1 unit | $9.92 | |
| Labor | Operator
(starting level molding and casting worker) |
$6.22 | Career Explorer | 2 hours | $12.44 |
| Prototyping Engineer (You!) | – | – | – | ||
| Overhead | Facility Cost (Machine Time) | None | – | – | – |
| Quality Control | $6.22 | Self (part of operator rate) | 1 hour | $6.22 | |
| Design | Engineering and Development | – | My own finger | 22 years to grow a finger? Haha | – |
| Iterations | 3 | Self (part of Quality Control) | – | – | |
| Misc. | Waste and Scrap | Alginate molds and failed casts
(material waste) |
Self | – | – |
Total: $69.51
COST ANALYSIS SUMMARY
This is the cheapest project we have analyzed so far and is relatively easy to complete. The total of my cost analysis came out to about $70, which included all of the materials and equipment. All of the materials are also easily accessible to anyone. I was surprised that there were sources for the rate for a “Molding and Casting Worker”. The top-level molding and casting worker earnings begin at $11.02/hr, but since this is my first time trying this process, I used the starting rate for a starting-level molding and casting worker at $6.22 per hour.
