It is made out of the steel tank inside a water heater after stripping off the shell, insulation, wiring and pipes. I cut off the end caps to lay in the insulation. In this case one inch thick Inswool. Then the end caps are tack-welded back on.

One end becomes the entry port for the burner.

The other is an open door to put in the blades.

Using the T-rex burner I can heat it up quickly to the austenizing temperature required for the particular type of steel.