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Assignment 7: Molding and Casting

Molding and casting are harder than I expected. I only had one casting experience: when undergraduate I casted a mental gear with the mold made by sand. This week I experienced the whole process of this craft.

Mold design

Because I want to do a small table droid with an eye, I decided to design the movable eyelids and fabricate them. I designed two pieces of eyelids which can be connected and assembled.

Final project sketch:

Then I tried to place them into positive mold. I got super confused in this step. My geometry seemed to be hard to mill because the bottom was narrower than the top. Then I realized I was going to cast something with a thickness instead of a volume. When I am doing something with thickness I need to make a two part mold for that piece so I can cast the shape in between. Because of that I will actually need to produce multiple molds for each part. Taking one piece of eyelids as an example, I would need to mill the underside of the part so I can cast the spherical part. Then I will need to mill the top portion for the other spherical part.

Trying different molds:

In order to make the geometry clearer in my mind, I 3D printed the eye structure. That helped me a lot in molding placing. Finally, after adjusting some details, I made my mold in rhino and got ready to machine.

Mold dmachine

I used mastercam to set up my file, and CNC to mill. In "make something big" week, I learned to use mastercam to cut 2D geometry. However I was not that confident with the complicated mastercam at that time. This week, to set up the mastercam file took me half a day. Now I am comfortable with this software:

Important notes when setting up:

When the g-code from master is ready, machine set up is easier. Important notes:

Machining my file took one and half an hour. My wax mold turned out to be smooth!


There are two steps for casting. First, making negative by silica. I built a paper box for my mold, mix up the oomo, tapped them Then I used release on my mold, and then poured the oomo into the mold. I left them for one night. Actually, 60-90 minutes are enough for oomo to become solid.

The second step is gypsum. I chose the grey one. The proportion of water and gypsum is 1:3. Actually, for my project I only used a little gypsum. Before pouring, two important steps:

1) Applying release. Otherwise the gypsum would be hard to remove.

2) Tapping the mixed gypsum. After pouring, knock the mold for preventing bubble.

I left them for one afternoon. My final work:

The angles and curves are perfect! Compared with 3D print model, it lost some details, but I enjoyed the process of casting! Also, special thanks to Liz and Justin, they gave me a lot of very useful advices when setting up mastercam!