Process

This assignment was well-introduced to us during class, which minimized a lot of the normal troubleshooting. To start, I mixed alginate and water into a mixing cup, using a ratio of 33 grams of alginate to 150 mL water. After mixing thoroughly, I stuck the middle and index finger of my left hand into the alginate, being careful that they were sufficiently far apart both from each other and from the sides of the cup. I then waited for the alginate solution to solidify, and carefully took my fingers out of the alginate.

In process of molding fingers in alginate

Next, I prepared the rig for adding screws into the plaster fingers before preparing the plaster. I taped two screws to two popsicle sticks, and carefully taped the popsicle sticks to a jig that fit over the top of the mixing cup. This step was done very carefully, as the set-up was not particularly stable and it was important that the screws entered the plaster at an appropriate depth and also approximately in the middle of the fingers for the sake of stability.

Rig for solidifying plaster around screws, pre-plaster being added

After confirming that the rig was set up well, I removed the rig and prepared the plaster solution in a different mixing cup. While the plaster packaging recommended a 2:1 plaster to water ratio, I used closer to a 3:1 ratio based on advice from a classmate. After preparing the plaster and mixing thoroughly, I poured the plaster into the holes left from my fingers. I could tell there were air bubbles left, so carefully used the popsicle stirring sticks to try and release the air bubbles. After pouring, I added and readjusted the rig then let the plaster harden for four hours, before carefully removing it from the alginate.

Plaster and rig during waiting step

After removing the fingers, I noticed that in one of them there was a slight concavity due to an unremoved air pocket.

Concavity due to air pocket

To fix this concavity and restore the shape of a finger, I prepared more plaster and carefully ‘painted’ it into this cavity. I then let this new plaster dry overnight.

Concavity filled with repair plaster

After all the plaster was hardened, I could post-process the fingers. I chose to spray paint the fingers green, adding two layers of spray paint.

Spray-painted fingers

After these coats were added, I added a coat of a clear sealant to complete the assignment. After, I made sure the workspace was clean (forgot to take a picture but remembered to clean…).

Finished Finger hooks.

Cost model

Cost Type	Cost	Price	Source	Quantity	Total
Materials	Skullduggery Perfect Molding Material	$13.99 /28 oz	Jo-Ann Fabrics	2 oz (1/14	$1.00
	Dap® Plaster of Paris	$7.99/4 lb	Michaels	0.25 lb (1/16)	$0.50
	Silicone mixing cups	$8.02/5	Amazon	2 cups	$3.21
	Screws	$11.47/100	Home Depot	2 screws	$0.23
	Spray paint	$5.98	Home Depot	1/5 bottle	$1.20
	Coating spray paint	$5.98	Home Depot	1/5 bottle	$1.20
Labor	Molding and casting worker	$8.28/hour	CareerExplorer	1.5 hour	$12.42

Total: $19.76

This assignment had far fewer considerations for the cost model than typical, largely due to the simplicity of the assignment and lack of need for any specialized equipment or facilities for it to be completed. In fact, this entire assignment could readily be completed in the average home, which is why I omitted the typical facility costs from my cost model. Additionally, due to the lack of complex or novel design elements, I omitted the need for any design consulting or prototyping engineer in the cost model. Remaining, the greatest driver of costs were material and labor. Material costs in this assignment were already fairly negligible, and even with increased production would be expected to be driven down further, although with increased production, paying for facility use might become warranted. Labor costs were the most substantial driver of costs in this model, and would be expected to scale somewhat linearly in the case of increased production due to how I estimated hours spent, although certain steps could be done in parallel (ex. spray painting and production of plaster and alginate), making the projected costs slightly less than the linear prediction.