For this week’s blog I was tasked with molding and casting two prints of my finger that could be used as wall hooks. For this task I utilized alginate to create a mold of my finger and then utilized plaster of paris to cast the mold. To begin creating a mold of my finger I began mixing 33g of alginate with 33g water, for a 1:1 ratio, in a silicon container. Then I utilized a popsicle stick to mix the mixture until it was homogenous and then put my finger inside the mold in a slightly curled manner.
The alginate mixture in a silicone container ready to create my mold.
An image of my finger resting inside the alginate mixture to create the mold. For this mold I used my ring finger as I had paper cuts on both pointer fingers of each hand.
I left my finger within the mixture for 10 minutes until the mold had cured. Afterwards I began mixing a plaster of Paris mixture within a different silicon container. The ratio for this mixture was 2g of plaster : 1g of water. So for this mixture I mixed 20g of plaster with 10g of water and then mixed the solution until it was smooth with a popsicle stick. Next I poured this plaster mixture into the mold I created previously. Using the 3d printed screw holding jig given to us I inserted a screw, head first, into the top mold.
Plaster of Paris mixture before being mixed and poured.
After pulling out my molded finger I created another mixture of plaster and poured it into the mold once again, placing a screw into the mold with the jig once again, and waited another 12 hours for it to set. Then after letting the second poured cast sit for another 12 I took it out of the mold.
An image of my nail set up with the provided screw jig. This is an image from my first attempt of creating a mold of my finger. My mistake was not inserting my finger far enough into the alginate resulting in a cast of only a quarter of my finger.
An Image of what one of my fingers looked like after taking it out of the mold. Notice the excess plaster on the base of the finger, which was removed during post processing.
POST PROCESSING:
Next came the post processing cycle of this project, where I took both molded fingers and used 80 grit sandpaper to remove the excess on the base of the finger. After removing the excess came spray painting the fingers. For this I used black and white spray paint, I was aiming for a chalkboard theme so I started with an initial layer of black spray paint followed by some light sprays of white spray paint.
Post processing the excess off the base by sanding with 80 grit sandpaper.
An image of both my sanded fingers ready to be spray painted.
Images after spray painting both fingers. The coloring of this project was inspired by chalk boards and chalk dust.
The following cost model is created for such a project below:
| Cost Type | Cost | Price | Source | Quantity | Total |
| Materials | Sand paper | $9.04 | https://www.homedepot.com/ | 1 | $9.04 |
| Screws (110 pk) | $12.38 | https://www.homedepot.com/ | 1 | $12.38 | |
| Alginate molding mix | $11.99 | https://www.hobbylobby.com/ | 1 | $11.99 | |
| Plaster of Paris | $7.49 | https://www.hobbylobby.com/ | 1 | $7.49 | |
| Spray Paint | $9.99 | https://www.michaels.com/ | 2 | $19.98 | |
| Silicon Container | $8.99 | https://www.amazon.com/ | 1 | $8.99 | |
| Labor | Prototyping Engineer (You!) | $36.48/hr | https://www.ziprecruiter.com/ | 3/hr | $109.44 |
| Overhead | N/A | ||||
| Design | Engineering and Development | $60.70/hr | https://www.talent.com/ | 1 | $60.70 |
The total cost for this project was $240.01 according to the cost model above. There is no overhead cost included within this model as there was no special machinery used within this project. Overall this project was very successful, however in one of the fingers there were some small holes, which indicates that there were a few air bubbles present when I let the plaster of Paris set in the mold. When doing this project over again I believe the time that it would take me would be about the same but I would be able to produce a product with less defects. Below is an image of my finished products and my clean working space.
My final deliverable.
An image of my working space after cleaning it.
