This project is something I have been itching to try for several years now, but have been a little to chicken to try. It has always seemed a little too ambitious, even for me. However, when I finally just decided to DO IT, it was really easy.
Looking at Backyard Metal Casting and other sites led me to a really cool set of books written by David Gingery. His premise was that anyone with enough desire and common hand tools could build their own metal shop it they wanted to. He has a set of 8 books that tells the reader how to do just that. His first volume -- The Charcoal Furnace, sets the stage. Using very common and inexpensive material Gingery shows the reader how to make a foundry to melt and cast aluminum. What is cool about his series is that the tool you make in volume 1 allows you to make the tool from volume 2, and so on... This leapfrogging of technology builds your skills to complement your shop. You never end up in a project that you don't have the skill to finish if you follow the progression of the series.
So on to the foundry...
I had an old popcorn tin lying around, and I bolted it to a lawnmower body I had left over from making my lawnmower generator. I drilled a hole about 2 inches from the base of the can so I could insert an air pipe later.
I then cut some circles of plywood using my table saw and built a metal tube to act as a form for my foundry. In the video below I tell you I used flashing instead of the sheet metal Gingery suggests in the book. I do that for two reasons -- the first was that I don't know anything about sheet metal, and the second was that I had a roll of aluminum flashing already. I find out later that Gingery used thicker metal on purpose. The thin flashing deformed as I rammed in the refractory. I repaired the mistake, but had I listened to the instructions I would not have had too.
For the refractory I went to the local big box hardware store and bought a hundred pounds of play sand -- that was less than 10 bucks. I also looked around for a bag of fireclay -- which I ended up getting at a local ceramics store. That was $8 dollars for 50 pounds. While I was driving I went to the goodwill and bought a hair dryer for $2.50. So using scrap I had, I spent less that $25 to have the capability to melt and cast aluminum.
I mixed the sand/clay mix in my wheelbarrow with a 2/1 ratio. I mixed this very well before I added water. It does not take very much water to do this. If you use too much water you will mess the mix up. Also wear a mask as the fireclay is very fine and makes a lot of dust. (I didn't and ended up coughing a whole lot). The idea is to make a very thick mortar. When you have just enough water sprinkled in and mixed so that you can make a ball of mix and break it into two clean sections you have the right mix. I then covered this mix with plastic and let it sit overnight so that the clay can absorb most of the water.
When I was ready to pound sand (LOL old military term), the first thing I did was to make a lid for my foundry. You have to make the lid first as you need to use it to finish the foundry. I did not follow the directions in the book exactly here either, but I don't think (at this point) I screwed up. I drilled a 4 inch hole in the center of the lid, and cut some flashing and bent it around the inside of the popcorn tin lid. I drove in some nails to point toward the center of the lid. I also punched some holes in the flashing and wove some wire between the holes like laying rebar in a concrete form. I also installed some u-bolts in the lid top so I would have a place to grab the lid. The next step is to fill the lid with your refractory mix, I tried to use a coke can as a form, but it deformed from the pounding I gave the sand to compact it. Once I pulled the can out of the lid, I used a piece of pipe to punch out the hole in the center of the lid.