For this week’s assignment, our class definitely topped the list of “creepiest prototypes seen around the OEDK”. After several days of molding and casting, the prototyping tables upstairs were littered with plaster copies of various fingers. Ignoring the obvious difference in material, the sight was a bit reminiscent of ‘House of Wax’.

Now, I am a horror movie fanatic. So I was pretty interested in this week’s assignment, especially since I had only done molding/casting once before. I had used alginate for molding and made a concrete copy of both of my hands interlocked. Yet for ENGI 210 we had to used slightly different materials, which would be a challenge.

I started out by making a mold with alginate and water. The instructions called for 4 oz (by weight) of alginate to 16 fl oz of water. Knowing that my hands were way too small for all that material, I decided to half the amount used. I mixed 2 oz alginate with 8 oz water in a cup and mixed until it had a milkshake consistency. One OEDK hack that made the process a lot faster was using a drill with a flat bit for mixing instead of a whisk. #unconventionalengineeringwisdom

 

As seen in the picture below, the mixture becomes bright pink when the two components are combined. This mixture is exciting in that the color changes to white when it is ready for molding. I placed my finger into the mixture when ready; however, because my hands are so small a couple of knuckles also joined the mold. This wasn’t a big deal since I knew I could simply cut the extra plaster off later.

While the mold dried, I tried to figure out the right combination for the Easy Flow. The bottles called for equal parts of A and B. After talking with Josh who had already finished the project, he told me that one half of a small plastic measuring cup (like those used for dispensing medicine) would suffice. I mixed the equal parts in a clean cup, stirred, and immediately poured into my mold. I had to act precisely and quickly as the set time is 2 minutes. I could easily see the cast beginning to form, and once the top layers began to solidify I inserted a screw into the mixture. The assignment called for this screw so that the piece could be used as a wall hook. Because, obviously, who wouldn’t want random fingers sticking out of their wall?

About 20 minutes later, I was able to remove the cast to see if I needed to change anything. Aside from the extra knuckle, it came out pretty well.

The only downside was that I wanted a slightly more curved finger in order to hold objects. Thus, I repeated the entire process over and molded my finger at a better angle. After waiting for the cast to dry, I demolded it and ….

it was awful. Apparently, the Easy Flow must have combined with previous reactants in the cup and not reached the right consistency. The cast appeared almost cloud-like when I poured it, and it never solidified fully which made the piece break immediately. Using a new cup, I tried the Easy Flow again and made a slightly better cast. Even though I had poured slowly, an air bubble still got trapped in the mold so the underside of the finger appeared dented. But with the deadline approaching, I decided to move on to post-processing and just admit my prototyping failure.

 

For post processing, I used a dremel to cut off the extra knuckles and smooth the base. I then gently used a rasp to make the base less jagged. I finally used some sand paper to even out the base again. I decided not to post-process the finger itself for fear of messing up the details.

Overall, this was a fun assignment. I learned that molding/casting procedures must be followed exactly in order to create an accurate piece. Pouring too soon or not mixing well enough could make the piece extremely brittle or inaccurate. It was a good lesson in patience, and I only wish I had allotted more time to the assignment to really perfect the pieces.