Les Bonnes Choses

In case you're parachuting into the story and want to be able to easily jump through the narrative, here are links to the rest of my tale:
Prologue
Part 1
Part 2
Part 3
Part 4
Part 5

And so my story crosses over into March. If you're playing along at home, you're sitting there with a bunch of prototypes ready to multiply them like so many loaves and fishes. It turns out it's easier than it might look at first.

I researched the heck out of the mold-making process, and found a handy website run by Alumilite, a company based out of Kalamazoo that sells plastic casting materials. After a fair amount of research (I discovered them back in the fall but didn't buy the materials until January) I decided on their Quick Set silicone rubber (for the molds) and their Alumilite Regular urethane plastic resin (for making the tiles). Here's the tricky part: how much did I need?

High school math to the rescue (stay in school, kids). They have volume calculators on their website, though they only calculate volumes for squares and cylinders. I wouldn't care for them much anyways because they were all in imperial units, which are crap. I had done some displacement measurements on my prototypes and found they all came in at about 25 ml. By my count, I needed to make 110 tiles, so the most cost-effective option was the 1 gallon jugs of resin, which would yield over 200 such tiles. The silicone rubber purchase was more difficult, though I went with the 5 lb tub to ensure I'd have plenty. It turns out I used too much rubber in my initial molds anyways (and then accidentally melted them) so it was just as well that I bought that much.

Making a 1-piece mold involves placing your prototype in a cylinder (people often use PVC pipe) or box, and then pouring liquid silicone over top of it. After the silicone sets, because it is naturally nonstick, you can remove your prototype from the mold and remove the mold from the cylinder. You just need to make sure that you pour an adequate amount of silicone in your and place the template that the walls of the mold are thick enough (a half-inch or about 15 mm between the edges of your prototype and the walls of the cylinder or box and covering your prototype is fine).

I first used as a mold box a Crisco container from which I had removed the bottom using a can opener. Its diameter and the formula for the volume of a cylinder of a height equal to 15mm higher than the thickness of my tile was used to calculate how much silicone I would need for each mold (and can be used to estimate the amount of silicone rubber to purchase).

Mixing up the silicone was my least favourite part of the whole project. It has a similar consistency and smell to white glue or perhaps latex paint, and makes a mess. I didn't wear gloves, but often wish I had. It doesn't stick to anything after it sets, but the same can't be said for its component ingredients.

After mixing up the silicone, I set my prototype in the middle of a base (in this case, the lid of the Crisco container), fixing it in place with dabs from a hot glue gun.

Sealing the container over the upside down lid, I then poured the liquid silicone over the prototype, and jiggled the container for a minute or so to try to coax bubbles to the surface (bubbles and air pockets in your mold are not desirable).

Eight or more hours later, you've got a mold!

Flip your mold box over, remove the base and then carefully remove the mold from the mold box and finally remove the template piece from the mold.



In the end, I decided that three different types of molds would suffice. I'm sorry today's installment wasn't even notable in its geekiness. A necessary evil, I'm afraid, if I am ever to get to the chilling conclusion to my tale.