Iterations on a Porcupine

Molding & Casting

This week was super fun! We experimented with designing in 3D, milling the shape, molding from the mill, and casting from the mold.


I wanted to use this week as an opportunity to experiment with CAD software. Adina gave me an awesome SolidWorks tutorial but after trying to install it on my Mac and realizing I needed to install Windows and run it in VM, I decided this was waaaaaay overkill for anything I was going to be doing in 3D.

I tried playing around with Inventor but finally settled on FreeCAD because it was the most similar to SolidWorks (and free!) I decided to make a simple form that invites people to touch it - like a porcupine with rounded quills that you want to pet.

After doing the Modela and the Desktop ShopBot workshop, I decided to mill it on the ShopBot because it was so much faster and I'd be able to make a bigger form.

It took about an hour and 15 minutes to make it on the Desktop ShopBot. I used a 1/8" ball endmill and put it on 3% stepover to try to get it to be the finest possible resolution.

Nice work Desktop ShopBot!

Another view.

So, I accidentally made my first mold with polyurethane. Why? Because the bottles were sitting on the table and I confused them with the silicone. Once I mixed it I decided to go ahead and try it out, however I think I got the ratios wrong. I did 1 Part: 1 Part B by weight but it should have been by volume. So I have a urethane mold but it's a little sticky and John was not happy with me. Also the urethane took forever to cure - I left it over the weekend.

I made a silicone mold and put it in the vacuum chamber to try to get all the bubbles out.

This worked great.

I started casting.

It was proving very hard to get the drystone to go into the tiny cones on the top of the porcupine. I decided to try a syringe.

This worked ok but I still ended up with some missing cones. Neil taught me the trick of pricking each cone with a sharp object to get the air bubbles to surface. I cast a couple doing both the syringe and the pricking technique.

And I forgot to say I was using tempera paints to color these. This worked more or less OK but the colors were kind of hideous Easter egg pastels since the drystone is so white.

More casting. It was pretty fun to just hang out in the lab this week and chat with people about their projects.

My last try. I really want to make ONE of these where the cones turn out properly.