It's easy and quick to make, I will show in this instructable the steps on how to make it using materials some of us have in our house. The only "big" money might be the refractory materials and characoal.
A few details about my furnace: I made it all 2" thick around including the furnace lid. I used Plywood, MDF, cardboard, chipboard all left overs from other jobs.
The furnace tools I made from a 5mm construction rebar, can of beans and old bathrooms hooks.
In the near future I hope to add to this instructable a few images of my first sand casting.
A few Saftey words: Coming into contact with fire and boiling melted metal can be very dangerous so always work safe using proper full body protection including respirator mask against toxic fumes and dust from mixing refractory materials. Never melt in a wet area or near water, if water comes in contact with the boiling aluminium it might "blow" in your direction.
Step 1: Furnace construction
I used scraps of plywood, MDF, chipboard, soft wood, cardboard all screwed together.
Start with the walls and the base. Optional: making small wooden angles for the corners will make the corners flat preventing them from breaking.
Drill a hole 2" from the base using a core bit for timber. The diamater of the hole should fit the size of the pipe you will use for the blower.
I used a cardboard pipe to form the opening for the blow pipe.