Molding and Casting

Design

This week, we were instructured to design and mill our own mold and then cast it. I wanted to do something related to my project, but I couldn't think of a way to integrate a cast item into the bag. Therefore, I decided to cast an accessory for my Halloween costume, a soot sprite from "My Neighbor Totoro"

I found the above mold from this website and decided to try to replicate the design in OpenScad. Most of the work involved individually tweaking the eyes.

Although we were warned multiple times in class, I inverted the first mold design. (I wanted the eyes to "pop out" and I had them "popping in" in the design.

I also had to change the design to make the edges smoother and change the orientation of the cuts. At first, I had all the cuts between pieces be directly straight down. I had to change that due to the design rules, so that the cuts were slightly slanted. In order to do that, I had all the cylinders have a larger top radius. I originally wanted the edges to be spikey, so I randomly chose a set of rectangles to cut out. Again, due to the design rules, I could not make sharp turns in such a small area, so I changed the cutouts to be cylinders, which looked nicer. The eye pupils also had to be expanded to have a radius of .06 of an inch, (.12 diameter) so that it would be sufficient for the 1/8th inch endmill.

Milling

When I was ready to mill, I exported an STL file from OpenSCAD as input. The STL generated in OpenScad is not great, so the first thing we did was load it to the mill computer and make it a binary STL file. I did one rough cut (with a 1/8 inch balltip endill) and one finer cut with the same endmill. This was at the TA's recommendation. I used the Shark machine.

We did have a couple mishaps. Firstly, we didn't center the design at the lower lefthand corner in the software. Therefore, we had a couple hiccups. We also forgot to turn on a part of the machine so it got stuck.

Molding

Once I milled my machinable wax, I had to clean the wax; a lot. For some reason, a lot of the wax bits got hot and stuck around. I went in with a sharp object (needle-nosed tweezers) and tried to scrape out as many pieces as I could.

Although the OOMOO says to do equal parts of solution A and solution B, that is per volume. It is actually 1 part of solution A and 1.3 parts solution B by mass. I slowly poured in the solution and let it sit for 2 hours.

The final mold looked pretty good! The eyes even came out!

Casting

Unfortunately, some of the outline features did not come out on the machinable wax, so I had a few places of leakage on the molding sides. To deal with this, I clamped a couple wood pieces on the sides.

The final cast looks ok! I wish it had a bit more details, but I ran out of time.