Project 06: Molding and Casting

For this week, I knew I wanted to make a chocolate mold. My initial idea was to create a chocolate shot glass, but this proved a poor fit. While I did come up with a few ways to create a positive out of wax (one for a two-part mold, one one-part), they were all inordinately difficult and complex compared to just creating my mold from an actual shot glass.

Instead, I decided to make something simpler: chocolate lego bricks. I made a simple one-part mold, rather than deal with making a two-part mold that would allow them to stack.

My model turned out to be a very instructional example of what not to do in many different ways:

• The space between the brick pegs was on one axis narrower than the tool size, meaning it wasn't possible to do a clean cut
• The design was large enough that it didn't leave room for walls, meaning I had to improvise. I designed around this originally, but didn't leave enough space between bricks and needed to adjust on-the-fly, creating this problem. Humorously, I improvised and used PCBs to create the walls (rather than be wasteful, I was able to wash them and return them to the bin when I was done.)
• I used a ball end-mill, which for my specific design meant the crisp edges I designed didn't come out properly. I should have used a flat end-mill.
• Although this isn't a problem per se, there wan't anything about my design that couldn't have been accomplished with 2.5d path planning; 3D path planning wasn't strictly necessary.

I did design a second model that fixed these issues, but didn't take the time to mill it.

Since my hope was to make chocolate, I needed to use food-safe material. I used Sorta-Clear 37, which was incredibly convenient: it mixes in equal parts by volume, making it very easy to prepare, and it has a pot life of 25 minutes and a cure time of only 4 hours.

That being said, it was significantly more difficult to work with than Oomoo would have been. It is incredibly viscous, and turns out to be very prone to bubbles. We ended up placing it inside the vacuum three separate times: as separate unmixed parts, after it was mixed, and after it had been poured into the mold. Even with all that, I was worried, as it still looked very bubbly on the surface.

I had no reason to worry, though. After curing, even though the top surface was still very bubbly, the rest of the mold turned out beautifully. Finally, the name "sorta-clear" was apt!

Shot glass!

After completing this, it hit me that we were going about the shot glass idea the completely wrong way. So Eric and I gathered again in the fab lab to do something far simpler: we made a mold using an actual shot glass!

This time, to help it come out even cleaner, we left it in the pressure pot overnight.

The result was absolutely gorgeous. A perfect mold. A quick cook in the oven to make it properly food-safe, and it was good to go!

As an initial test, I used it to make an ice shot glass. The ice itself wasn't great - making perfectly-clear ice is a project in and of itself - but the shape turned out great!