The theme of this week was molding, casting, and composites. The assignment was to design and machine a mold, then cast something in it. It sounded easy, until I realized I have very, very poor 3D reasoning skills. I mean, negative molds I can reason about, but positive molds? I need a mold that’ll cast a mold that’ll cast an object, right... And don’t even talk to me about 2 part molds!

Half an afternoon of playing with molding clay later, I finally had a good grasp of positive molds. I was going to make a labbit, but then decided to make my own design instead. This is what I came up with:

I exported my cat model as a .stl file, and took over to the Modela.

This is where I learned about 3D tool path generation. There are two passes involved. First, a rough pass that cuts in the xy plane, then a finishing pass that cuts in the yz and xz planes.

Unfortunately, being the first one to use the Modela, we didn’t realize that we can turn the speed setting all the way up to 20 mm/s (I should have reviewed my notes from class!). So, the Modela chugged along at a leisurely 3 mm/s.

About 4 hours later, I had the rough cut finished.

I did the finishing cuts using the proper 20 mm/s speed, which took another hour or so.

Here’s the finished mold, together with my initial clay model. The finishing cuts gave a really nice finish on the wax!

The casting part was a blast. For once, there are no machines involved. Just good old fashioned mix n’ pour. It reminded me a lot of baking, actually.

Here’s the negative mold, done in Oo-moo (a kind of silicone).

I cast the cats in both drystone and hydrostone. The hydrostone ones are gray, the drystone ones are white. They’re cute, aren’t they?

I embedded magnets in some of the cats as well. My initial design was to make cats that would want to kiss each other. The magnets ended up in all sorts of directions, so I had cats that disliked each other instead. Still cute.

Then, I thought, why not decorate the cats? I gave the cats a coat of varnish using clear nail polish, and decorated them with sharpies.

And of course, the assignment wouldn’t be complete without something edible.

I got some food-safe silicone from Natalie, and made some chocolate cats.

For future reference, molding chocolate cats is such a pain, it’s not worth the first. First, one must temper chocolate to align its crystalline structure (heat to 118F, cool to 81 F, then heat back up to 86F). Then, the cat tail inevitably breaks off during the unmolding process. Urgh.

Modela Settings

Rough cut:

overlap: 0.75

speed: 20 mm/s

3D settings:

1. -select xy cut
   

2. -z step: 1 mm
   

3. -z top: 0 mm
   

4. -z bottom: -31.75 mm (the height of the wax)
   

5. -top intensity: 1
   

6. -bottom intensity: 0
   

Finishing cut:

overlap: 0.1

speed: 20 mm/s

3D settings:

1. -select xz finish and yz finish
   

2. -z step: 1 mm
   

3. -z top: 0 mm
   

4. -z bottom: -31.75 mm (the height of the wax)
   

5. -top intensity: 1
   

6. -bottom intensity: 0