:: dogiChow ::

09 // Molding & Casting :: Interstellar volcano

This week we needed to get our hands dirty with some heavy duty molding. The last time I played with hydrostone I burned myself pretty badly so I knew that I had to use it again. I decided that I will make a volcano out of concrete (here hydrostone) that will have fiber-glass embedded inside, so the volcano can light up. Originally I wanted to hook it up to last week's EEG, so you could make the volcano erupt, but due to the problems with my circuit (it measures the number of squirrels sitting in the park, not my EEG signals) I just use a big LCD screen to make the fiber glass dance in colors.


I am seriously starting to like Rhino, once again I designed my pieces in it with the help of Shelby and Ella ^_^. The tricks are the following:

  • You need two holes on your mold: an air-hole (to get air OUT) and a hole where the casting material enters. Failure to provide those holes will waste your time :(.
  • If you don't make alignment pins to fit your parts together perfectly it will be hard, but not impossible to make a nice mold
  • Exothermic processes heat up materials. A lot.

After my design was done I had to choose between the Modela or the ShopBot. Since I hate the Modela I chose the ShopBot. The two parts needed two approaches: the bottom part was just a simple pocket, the 2D software of the ShopBot did the job easily in less than 15mins. The only limit in scaling my object was that the longest bit that we found with Tom was 2 inches long. That's the height of my volcano. I machined it out of foam which rips into small flakes that take forever to clean up.
The top part was machined with the 3D software that comes with the SB. It divides the process into roughing and smoothing. First it roughs the surfaces out with the process that we observed before in 2D and than it does an extra pass with a ball shaped end mill that smooth out the surface on a raster.


Hydrostone was the material of choice, which is great to work with, because it's cheap, not really toxic (I hope, but don't take for granted). You just mix it with water...you want to achieve Yogurt mixture, which comes around 1 : 5 :: water : hydrostone - ratio. Before mixing the hydrostone I embedded my fiberglasses into the top and the bottom of the molds, so that I they will be casted into the material.

Casting went smoothly. IMPORTANT: if you cast directly into foam, you want to put oil/soap on the surface of the foam, so you will be able to separate after it cures. The oil worked amazingly well, the volcano almost fell out of the foam when I applied force.

Some more pictures:

I wrote a little processing sketch to make some fake volcano fire: And some files to play around with (STL, DXF, PDE) FILES
Dögi's How to make almost anything? photoset Dögi's How to make almost anything? photoset