I made one of these a few years ago. After watching James may's Manlab. I found a set of books called Build Your Own Metal Working Shop from Scrap. The first book in the series is the charcoal fired foundry. It'll be a great project for retirement.
I haven't made anything in anger with it yet, but I had a go at making some zinc ingots from old wheel weights. I was using muffin trays as moulds which will give about 30mL ingots to make it easy to work out how many you need once you work out the volume of your piece that you're making. I got the used wheel weights from the local tyre dealer for nix.
I learned a couple of valuable lessons that day. Firstly not all wheel weights marked as zinc are fully zinc. some are just zinc coated steel. While melting them I was looking in though the furnace exhaust and stirring with a steel rod to check when they melted. They weren't melting so I kept the furnace getting hotter and hotter, and then finally decided to pour what I had.
The zinc poured out, and proceeded to weld itself into the muffin trays, so I destroyed them trying to get the ingots out.
Obviously too hot. If I'd only just melted the zinc it should cast in the muffin trays without a hitch.
The other little thing to watch for is the first time you fire it up to cure the refractory. It needs to be fired slowly so the moisture in the refractory doesn't explosively turn to steam. The other thing with these simple furnaces is you don't have a lot of control over the rate of combustion.
I fired mine up to cure the refractory with it set up about 10m from each of the house and the shed. At first it's not too bad, but the furnace is design to run with a reducing flame (i.e. not enough oxygen for complete combustion) so that the metal in the furnace isn't corroded. When it gets warm enough, the CO produced from the incomplete combustion ignites at the exhaust! This results in a 2-3m tall translucent blue jet of flame and a roar that is quite terrifying when you don't expect it!
10m from the house and shed was way too close IMO the first time I started it - but what could I do? It was alight, making scary noises, throwing sparks, and potentially heating the refractory too fast and could explode any minute... what could possibly go wrong?
It will emit heaps of sparks which are blown high in the air by the jet and these can travel a fair distance. Remember the sparks can still start fires at temperatures as low as 260°C which is a lot cooler than glowing, so you have potential to start unwanted fires very easily. I only start mine in winter, outside of fire season.
Now that the furnace is cured, and I know what to expect it's not so bad.
I'm happy to stand next to it and look in through the exhaust to judge temperature and the rate of melting.
What ever you do make sure you make a DRY sand area to work in when handling the molten metal. Concrete has too much moisture in it even then it is set - it you drop molted metal on the concrete it will explode and spray the molten metal everywhere - likely starting fires. You can't use water on a metal fire. You have to use DRY sand.
Because I hate what cats do to exposed sand, I have a long steel tray about 600 wide and 3600 long that I made a lid for. It is full of dry sand and I set the furnace up at one end, have an area to place the furnace lid and place the mold at the other end. If anything goes wrong I can just dump the molten metal in the dry sand.
I also have the full protective gear - face shield, leather boilermaker's jacket and apron (another reason to do this in winter). Make sure you wear leather boots! The last thing you need is a splash of metal igniting a synthetic shoe or boots which proceeds to burn and melt on your foot while you are trying to concentrate on doing technical things with a couple of kilos of molten metal!
No doubt about it, it's a MAN's hobby! Enjoy!
BTW there are a number of forums and groups on the web where you can pick up all sorts of info. The setups some of these guys have is amazing!
Al.
made lots of great counter weights though.
