This is my natural gas burner. It's overall length is 40 inches, seems kind of long but after days of experimenting this is what worked. It had a flame sensor inside the 1-1/4 pipe and worked well, too well, the sensor would also see the hot refractory. I removed the whole 1 1/4 section, which made the burner worse, so I put it back without the sensor.

The shinny disk is a vacuum switch; it's purpose is to shut off the gas in case the fan stops working. If the fan stops, the flame will shoot out the back which is no good. The fan, electric gas valve and vacuum switch are from a power vent hot water heater. The gas mixture is controlled by a damper on the fan and a gas ball valve. The gas hose is made for a natural gas barbeque.

This burner works great. I light a torch and hold it next to the tuyre, flick the switch and when the fan comes up to speed, the vacuum switch engages the gas valve and the burner roars to life. The 3/4 pipe can be easily swapped with a 1 in pipe for a larger flame. Good Bye Charcoal!

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The furnace is made from one of those driveway rollers that you fill with water. The refractory is made from 4 parts perlite to 1 part furnace cement and developed 2 large vertical cracks while curing. Looking down into the furnace is a crucible with two Honda rim ingots. You can also see how the furnace lid swings away. This design is better because the lid radiates it's heat at you when it opens upward.