Another safety note: you're working with a big container of potentially explosive gas, high pressure gas, and lots of potentially leaky connections. If you don't know what you're doing with gas plumbing, I *strongly* advise you build yourself a charcoal-burning furnace, as Dave Gingery originally intented, instead. Propane is very nice: it is hot, clean, and fast. However, it has a vastly higher potential for being dangerous. Don't work with things that can kill you unless you know what you're doing.

My burner is copied fairly closely from the burner developed by Ron Reil for use in forges. It consists of a foot-long piece of 1 1/2" black iron pipe, threaded on both ends (only needs one end threaded.) Onto the threaded end, is screwed a 1 1/2" - 3" adaptor (bell adaptor) which serves as the air intake. This bell adaptor has a 3/8" hole drilled in it, crosswise, in the 3" end, so that a pipe can cross the bell.
The cross pipe is a 5" piece of brass, capped on one end, and with a sensitive valve on the other. The valve leads to a hose, which leads to a regulator, which is in the top of the propane bottle. In the cross pipe, I've drilled a #60 hole, midway along the pipe, so that the hole faces directly down the iron pipe. The propane shooting out the hole sucks air down the pipe, they mix, and burn at the end of the iron pipe.
I feel strongly that the regulator and sensitive valve are really important parts of this. You want a good, safe, and adjustable setup. You also need to use sealer tape on all threads to prevent any gas leaks.
The cross pipe is held in the bell adaptor by drilling two small holes from the 3" face of the bell adaptor into the holes that the cross pipe will go through (*without* the cross-pipe in place.) These are tapped, and small set-screws go into them to pinch the cross-pipe. I also filed flats on the cross-pipe for more positive grip. It is pretty important to make sure the hole in the cross-pipe points directly down the burner pipe.
I light this by putting the burner in the side of the furnace, putting a handful of kindling (pine needles) in the furnace, lighting them on fire, then turning on the gas. It should make a roaring sound like a jet aircraft, a deep howl, and the blue flame should be fairly stable at the end of the iron pipe. If you don't have sufficient gas pressure, the flame will suck back down the iron pipe, making a high-pitched whirring sound that sounds like a cat hacking up a hairball inside a barrel. Cut the flame, drop some newspaper or pine needles into the furnace, and when they burst into flame, hit the gas again. Don't try and blow the flame back into the furnace by adding gas; it won't work. If the flame goes entirely out because something briefly blocks the burner nozzle, like a dropped piece of aluminum or a misplaced crucible, kill the gas, put some kindling in, and restart. Never let the gas run into a hot furnace; when it does ignite it does so with a highly invigorating WHOOMP. Don't do this.

I have a wooden rest that the burner sits on, made of a 2x4" scrap, so that it's not cantilevered out of the side of the furnace. I also have put an old nut can over the bell adaptor so that it is sheltered from gusts of wind; the open adaptor end is highly suseptible to gusty conditions and the flame stability suffers heavily. Open-cell foam would make a much better air filter.

This page written on 12/15/00, last modified 23 May 2023.

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