I built this furnace with some friends. We really didn't know much about metal working. We also had a very tight budget. This furnace was built out of normal house brick. The bottom of the chamber is rock to hold up the fire and to let the air flow up in to it. We used a hair dryer as the air source and charcoal briquets as the fuel source. The crucible was a stainless steel cup. Our goal in building this was to melt some copper. With this setup we could melt some of the lower melting point metals. Metals such as zinc and lead.
Here we updated are furnace using a number 10 can. Having a small space to heat helps us to get to higher temperatures. Also the hair dryer was blowing up a pipe made from smaller cans. Having the air flow more controlled also greatly helps in raising the temperatures. Now we could melt aluminum. Also the stainless steel cup was now to small, so we got a larger crucible. We used cans for aluminum but found that they would fall apart just as the copper started to melt. We tried making a crucible out of half inch pipe, sadly, because of are limited equipment. It was not sealed at the bottom. So when the copper melted it came out the bottom. Also the bottom of the crucible, being covered in molten copper, started to melt as well.
Finally to reach are goal of melting copper, we chose to got a crucible from a friend. They had ordered them online. They were made of graphite and after tempering them the best we could, we used them in our work. They work perfectly and we melted copper in a furnace made of scrap around the house and briquets. After doing this, I have to say it was a lot of fun. Trial and error was a fun way to learn. Lastly if there is something you want to try. Just do it and don't stop until you find the way to make it work.