Week 6

1. Preparing the wax mold

For this week, I have a choice of using SLA 3D printers or milling the wax block to get the mold for casting silicone. Although SLA printers are easier to achieve more complex shapes and more straightforward, and I can imagine myself using this way more often in the future, I do want to learn how to use a table top milling machine, so that’s the way I chosen for this week.

I’ve planned to use the food-safe silicone to cast some chocolates. I want to make something interesting with simple geometry, as I am still learning and am very bad with Fusion, and want to just start with a one-part mold. As a result, I CAD a cat/dog bowl, which I imagine you’ll be able to pour in a tiny bit of milk in the middle and eat it with the chocolate, which should be fun and delicious.

The design with the block of wax looks like this:

Then I need to generate tool paths for this, setting up adaptive clearing with the 6.35mm flat endmill, and parallel finishing with the 3.175mm ball endmill. Since I want a smoother finish, I set up two parallel finishing, one along the x-axis and another along the y-axis. After checking the generated tool path and simulating the milling result, which looks fine, I sticked the block on to the copper board and clamped it down on Genmitsu. After setting up the origin of my block, it’s ready to mill.

The rough pass took ~35 mins, and each of the fine pass took ~14 mins, which can be a little bit faster if I have raised the floor of my design a bit, since I originally planned to make it taller, and at the end the top layers (the first 10 mins of rough pass) are kind of just a waste. No matter what, the final result looks pretty nice! The finishing surface is pretty smooth and it’s just nice when it milled as you’ve intended to. (The first try was not succesful as I CAD the stock body wrong, and I didn’t check the simulation result, and the mill started at a wierd position milling out a deephole, which I quickly stopped the machine and redo the design. Forgot to take picture of it so just documneting it with texts)

2. Making the silicone mold

I then casted it with Sorta-Clear 37 which is a food-safe 2-part silicone rubber. It is very gooey and traps many bubbles, and the vaccum is not strong enough to get rid of all of them. I decided to just pour the bubble-rich top portion first into somewhere not important, and pour the better ones as the first layer of my model and hope it turns out fine. After waiting overnight I’m very glad to see the silicone mold curing nicely and none of the bubble ruined the surface!

3. Making the chocolate

I am aware that the wax and the endmills mat not be food-safe, but I think it should be fine if the food-safe silicone is cleaned thoroughly(which I did), maybe I can’t sell these chocolates but I am pretty comfortable eating them myself. I microwaved the chocolate chips at a 30 sec interval until it’s homogenous and in the liquid form. I then poured in into the silicone mold and put it into the freezer for 8 mins. There are some bubbles on the rim though, but after some inspection I confirmed that it is not the mold’s problem it’s just the casting of chocolate, which is not a huge problem. After some more batches of practice, the yeild rate of making a perfect rim is still pretty low, which I think can be significantly improved if I keep the chocolate warmer or even preheat the silicone a bit, since I don’t really know the pot life of the melted chocolate in room temperature, and the best bet might be keeping everything warm. The majority of the chocolate turned out nice though, which I am happy about it for now.

I just made the chocolate before class, and I’m testing it in class with milk, hope Neil trust the food-safe process enough and try one as well. I also brougt a sterile syringe for transferring the milk to the bowl.

4. Group Assignment: Casting with Marcello

For the group project, Marcello showed us how to cast the silicone rubber and we made Oomoo-25 silicone mold of the CBA keychain. After curing we then poured Smooth-Cast-326 to make the keychain itself.