The main squeeze. Built in a 20 gallon steel trash can, with a 3" tuyere (pronounced 'tweer') and 1" drain hole in the bottom. 8" inside bore, 3" walls. A great piece of furnace! And yes it consumes the wood pile seen to the left. I moved from expensive, messy briquette charcoal to easier-to-burn wood.
I patched the inside last month after at least 20, maybe 50 burns. By and large, this stuff holds up very well, however thermal cycling stresses it - the area in front of the tuyere and the lid are taking a bit of damage, though nothing a bit of furnace cement hasn't fixed yet. (I'm always taking the lid off to put in more wood, this puts it from 2,000°F+ on the furnace to < 100°F on the ground; while I'm messing around inside, I turn down the air blast, so the tuyere cools down a bit too, and gets the same kind of stress.)
If I recall correctly, the recipie is three parts wood ash, one part sand, one part rubble (see below) and one part Portland cement to bind it all together.
11/25 (hmm that's the first time I've ever indicated a date... for reference, this page was created on 3/27/03.) With the propane it only runs maybe 1400°F inside the whole thing, and that's with the big burner on high; it isn't really all that good stuff. But I'm not paying $175 to redo it with commercial refractory, so I'll keep it.
Made this fall 2004. As the above furnace is too big, too bad an insulator and too worn out (I never realized the ash content is actually a flux...), I now use this guy for a lot of work. For casual aluminum melts, I get out a reverb. For bronze, they melt slowly, can't get quite hot enough and leave the bronze gassy besides, no good for casting. This thing does it flawlessly. I also use this for controlled heating such as when making master alloy or firing ceramic.
My main man. I use this almost exclusively now. In fact the only times I haven't used it were when I was low on propane and had to burn charcoal in the trashcan furnace above. It has about as much capacity as a tomato-can crucible, 6 pounds of molten aluminum.
When I need to melt a lot of aluminum, this guy gets going, and it gets going great. Holds 15 pounds of aluminum, molten in a little over a half hour. O maker of ingots, enemy of dirty scrap everywhere!
Not much larger than the minifurnace, this is just two hollowed-out firebricks - but it gets the (small) job done. Lots more details on its page. The only time I've got this out recently (~02-2004) was for another small bronze melt. 03-2005: Basically dead now. My crucible furnace has taken over the duties, with higher quality to boot.
Built in a coffee can, this cute guy sports a 4" bore, and is light enough to hold in one's hand. I use this for small melts - zinc for instance - firing it with small-sized charcoal (left over from either the big furnace or the fireplace), or as the oil burner for the big furnace above. Its original purpose was to test the new refractory recipie used in the big furnace, and so far it has shown good promise.
I also heat-treat small blades in it, but that's a story for another section of this website! :)
The new design based entirely the perlite/furnace cement refractory. This baby got me through a bit more melting, but I soon realized I'd need a larger furnace; 6" bore is too small.
I soon tired of patching this furnace, and eventually did an autopsy when it got a fatal blockage in the tuyere. This wasn't the first - one time I had got some zinc too hot, it burned through the crucible and spilled into the furnace, and not having a drain hole it ran into the tuyere, and since the tuyere is made from galvanized sheet steel, it soldered itself right in. This was a loss of a good bit of zinc, but not fatal to the furnace.
The fatal blockage was when I was breaking up some large chunks of aluminum; it melted, and not having a crucible to hold it, ran down into the tuyere. This aluminum (being right at the melting point) froze much earlier, bunching up and eventually clogging the tuyere.
As a final rite, I broke up the refractory. Then the thought came to me to put the rubble in the new furnace! So indeed, the old furnace lives on.
The original, what I built when I first got into casting. The very first model used wood ash for insulation - pretty good stuff, but obviously won't hold its shape - so I used two stacked coffee cans for the inner form. This wasn't workable in the long run since I was replacing the inside every time, as it got very crunchy and oxidized (but proof that it was getting quite hot inside).
Pictured is the first burn of a slight variation - I used perlite-and-furnace-cement-based refractory, plastered on a cardboard form (which obviously burns out) with ash packed in around it. Unfortunately this also cracked up, so I was again out for another design.