This assignment involved making wall-hooks of of fingers that can be screwed into a wall for hanging objects with molding and casting techniques.
First, we created the mold out of alginate. This involved mixing a 1:1 ratio of the alginate to water. I used appx. room temperature water. After combining the 1:1 alginate to water, I began to immediately mix the combination for about 4 minutes. After mixing for 4 minutes, I inserted my finger into the now gelatin-esque mixture. I noticed that when I initially started mixing the alginate turned from white in color to pink in color, but it again returned to white right around after I inserted my finger (~4-5 minutes after mixing).
I was a bit concerned that I did not use enough alignate/water to create a successful mold and it would just turn out to be a stub of a finger, but I was able to reach most of my index finger into the mixture. I noted the angle that I inserted my finger so that I would be able to hopefully repeat the same design. After about 5 minutes, I pulled my finger out slowly to preserve the mold. I then worked on inserting the plaster. I mixed the plaster in an approximately 2:1 ratio of plaster:water for about 3 minutes before pouring it into the finger mold. The plaster seemed quite runny, but I decided to proceed with the initial 2:1 ratio. Placing the screw was quite difficult since the plaster mixture was so runny. I used tape to attempt to hold the screw in-place. It worked to keep the screw positioned upright, but I don’t think that the positioning was optimal.
For the second iteration, I used the same technique and timing for the alginate mold. For the plaster, I used a ratio closer to a 4:1 ratio of plaster:water since the previous iteration was so runny. I noticed that the screw was easier to secure in-place since the plaster mixture was thicker, but it still proved to be a challenge and required the improvised tape holder. A future modification could be to laser cut a screw holder that could go over the top of the cup and hold the screw in-place at the appropriate height.
After around 25 minutes and then again at 1 hr, the plaster still had not set for both the runny (v1) and thicker (v2) iterations. I came back after about 3 hrs and found that the plaster had set nicely. I was able to successfully remove the finger hooks from alginate molds by carefully ripping the alginate around the plaster.
I noticed that in the runny v1 iteration, there were minimal air bubbles but the screw was clearly not as upright as it would be ideally. In the thicker v2 version, the screw was better-placed but there was a larger air bubble that could be seen. From these observations, an optimal combination could be thinner plaster mixture with a structured screw holder.
To post-process, I spray-painted the finger hooks with matte clear spray paint and let them dry.
Cost Analysis:
- Plaster of paris – $17/25 lbs (from ENGI 210 workbook)
- Alginate – $35/3 lbs (from ENGI 210 workbook)
- Screws – $8/250 screws
- Spray paint – $5/1 can
- Cups, water & popsicle sticks – minimal cost
- Labor Cost – $10/hr, 2hrs of labor
Therefore, to buy the base products required, the total cost to create one (not-scaled) finger-hook mold would
be $17 + $35 + $8 + $5 + $20 = $85.
This would decrease significantly with scale as the screws, plaster of paris, spray paint, and alginate cost would all decrease significantly with more units manufactured per purchase of bulk materials. If each of the materials were used to their full capacity, I would anticipate that the scaled cost/unit would be closer to the labor cost of $20, plus additional materials costs that become fairly minimal in comparison to the labor cost.
